QGIS Planet

(Fr) Oslandia recrute : développeur(se) C++ et Python

Sorry, this entry is only available in French.

QGIS 3 and performance analysis

Context

Since last year we (the QGIS communtity) have been using QGIS-Server-PerfSuite to run performance tests on a daily basis. This way, we’re able to monitor and avoid regressions according to some test scenarios for several QGIS Server releases (currently 2.18, 3.4, 3.6 and master branches). However, there are still many questions about performance from a general point of view:

  • What is the performance of QGIS Server compared to QGIS Desktop?
  • What are the implications of feature simplification for polygons and lines?
  • Does the symbology have a strong impact on performance and in which proportion?

Of course, it’s a broad and complex topic because of the numerous possibilities offered by the rendering engine of QGIS. In this article we’ll look at typical use cases with geometries coming from a PostgreSQL database.

Methodology

The first way to monitor performance is to measure the rendering time. To do so, the Map canvas refreshis activated in the Settings of QGIS Desktop. In this way we can get the rendering time from within the Rendering tab of log messages in QGIS Desktop, as well as from log messages written by QGIS Server.

The rendering time retrieved with this method allows to get the total amount of time spent in rendering for each layer (see the source code).

But in the case of QGIS Server another interesting measure is the total time spent for a specific request, which may be read from log messages too. There are indeed more operations achieved for a single WMS request than a simple rendering in QGIS Desktop:

The rendering time extracted from QGIS Desktop corresponds to the core rendering time displayed in the sequence diagram above. Moreover, to be perfectly comparable, the rendering engine must be configured in the same way in both cases. In this way, and thanks to PyQGIS API, we can retrieve the necessary information from the Python console in QGIS Desktop, like the extent or the canvas size, in order to configure the GetMap WMS request with the appropriate WIDTH,, HEIGHT , and BBOX parameters.

Another way to examine the performance is to use a profiler in order to inspect stack traces. These traces may be represented as a FlameGraph. In this case, debug symbols are necessary, meaning that the rendering time is not representative anymore. Indeed, QGIS has to be compiled in Debug mode.

Polygons

For these tests we use the same dataset as that for the daily performance tests, which is a layer of polygons with 282,776 features.

Feature simplification deactivated

Let’s first have a look at the rendering time and the FlameGraph when the simplification is deactivated. In QGIS Desktop, the mean rendering time is 2591 ms. Using to the PyQGIS API we are able to get the extent and the size of the map to render the map again but using a GetMap WMS request this time.

In this case, the rendering time is 2469 ms and the total request time is 2540 ms. For the record, the first GetMap request is ignored because in this case, the whole QGIS project is read and cached, meaning that the total request time is much higher. But according to those results, the rendering time for QGIS Desktop and QGIS Server are utterly similar, which makes sense considering that the same rendering engine is used, but it is still very reassuring :).

Now, let’s take a look to the FlameGraph to detect where most of the time is spent.

 

Undoubtedly the FlameGraph’s are similar in both cases, meaning that if we want to improve the performance of QGIS Server we need to improve the performance of the core rendering engine, also used in QGIS Desktop. In our case the main method is QgsMapRendererParallelJob::renderLayerStatic where most of the time is spent in:

Methods Desktop % Server %
QgsExpressionContext::setFeature 6.39 6.82
QgsFeatureIterator::nextFeature 28.77 28.41
QgsFeatureRenderer::renderFeature 29.01 27.05

Basically, it may be simplified like:

Clearly, the rendering takes about 30% of the total amount of time. In this case geometry simplification could potentially help.

Feature simplification activated

Geometry simplification, available for both polygons and lines layers, may be activated and configured through layer’s Properties in the Rendering tab. Several parameters may be set:

  • Simplification may be deactivated
  • Threshold for a more drastic simplification
  • Algorithm
  • Provider simplification
  • Scale

Once the simplification activated, we varied the threshold as well as the algorithm in order to detect performance jumps:

The following conclusions can be drawn:

  • The Visvalingam algorithm should be avoided because it begins to be efficient with a high threshold, meaning a significant lack of precision in geometries
  • The ideal threshold for Snap To Grid and Distance algorithms seems to be 1.05. Indeed, considering that it’s a very low threshold, the precision of geometries is still pretty good for a major improvement in rendering time though

For now, these tests have been run on the full extent of the layer. However, we still have a Maximum scale parameter to test, so we’ve decreased the scale of the layer:

And in this case, results are pretty interesting too:

Several conclusions can be drawn:

  • Visvalingam algorithm should be avoided at low scale too
  • Snap To Grid seems counter-productive at low scale
  • Distance algorithm seems to be a good option

Lines

For these tests we also use the same dataset as that for daily performance tests, which is a layer of lines with 125,782 features.

Feature simplification activated

In the same way as for polygons we have tested the effect of the geometric simplification on the rendering time, as well as algorithms and thresholds:

In this case we have exactly the same conclusion as for polygons: the Distance algorithm should be preferred with a threshold of 1.05.

For QGIS Server the mean rendering time is about 1180 ms with geometry simplification compared to 1108 ms for QGIS Desktop, which is totally consistent. And looking at the FlameGraph we note that once again most of the time is spent in accessing the PostgreSQL database (about 30%) and rendering features (about 40%).

 

 

 

 

 

Symbology

Another parameter which has an obvious impact on performance is the symbology used to draw the layers. Some features are known to be time consuming, but we’ve felt that a a thorough study was necessary to verify it.

 

Firstly, we’ve studied the influence of the width as well as the Single Symbol type on the rendering time.

Some points are noteworthy:

Simple Line is clearly the less time consuming

– Beyond the default 0.26 line width, rendering time begins to raise consequently with a clear jump in performance

 

Another interesting feature is the Draw effects option, allowing to add some fancy effects (shadow, glow, …).

However, this feature is known to be particularly CPU consuming. Actually, rendering all the 125,782 lines took so long that we had to to change to a lower scale, with just some a few dozen lines. Results are unequivocal:

 

The last thing we wanted to test for symbology is the effect of the Categorized classification. Here are the results for some classifications with geometry simplification activated:

  • No classification: 1108 ms
  • A simple classification using the column “classification” (8 symbols): 1148 ms
  • A classification based on a stupid expression “classification x 3″ (8 symbols): 1261 ms
  • A classification based on string comparison “toponyme like ‘Ruisseau*'” (2 symbols): 1380 ms
  • A classification with a specific width line for each category (8 symbols): 1850 ms

Considering that a simple classification does not add an excessive extra-cost, it seems that the classification process itself is not very time consuming. However, as soon as an expression is used, we can observe a slight jump in performance.

Labeling

Another important part to study regarding performance is labeling and the underlying positioning. For this test we decreased the scale and varied the Placement parameter without tuning anything.

Clearly, the parallel labeling is much more time consuming than the other placements. However, as previously stated, we used the default parameters for each positioning, meaning that the number of labels really drawn on the map differs from a placement to another.

Points

The last kind of geometries we have to study is points. Similarly to polygons and lines, we used the same dataset as that of performance tests, that is a layer with 435588 points.

In the case of points geometries geometry simplification is of course not available. So we are going to focus on symbology and the impact of marker size.

Obviously Font Marker must be used carefully because of the underlying jump in performance, as well as SVG Symbols. Moreover, contrary to Simple Marker, an increase of the size implies a drastic augmentation in time rendering.

General conclusion

Based on this factual study, several conclusions can be drawn.

Globally, FlameGraph for QGIS Desktop and QGIS Server are completely similar as well as rendering time.

It means that if we want to improve the performance of QGIS Server, we have to work on the desktop configuration and the rendering engine of the QGIS core library.

Extracting generic conclusions from our tests is very difficult, because it clearly depends on the underlying data. But let’s try to suggest some recommendations :).

Firstly, geometry simplification seems pretty efficient with lines and polygons as soon as the algorithm is chosen cautiously, and as long as your features include many vertices. It seems that the Distance algorithm with a 1.05 threshold is a good choice, with both high and low scale. However, it’s not a magic solution!

Secondly, a special care is needed with regards to symbology. Indeed, in some cases, a clear jump in performance is notable. For example, fancy effects and Font Marker SVG Symbol have to be used with caution if you’re picky on rendering time.

Thirdly, we have to be aware of the extra cost caused by labeling, especially the Parallel  placement for line geometries. On this subject, a not very well-known parameter allows to drastically reduce labeling time: the PAL candidates option. Actually, we may decrease the labeling time by reducing the number of candidates. For an explicit use case, you can take a look at the daily reports.

In any case, improving server performance in a substantial way means improving the QGIS core library directly.

Especially, we noticed thanks to FlameGraph that most of the time is spent in drawing features and managing the data from the PostgreSQL database. By the way, a legitimate question is: “How much time do we spend on waiting for the database?”. To be continued 😉

If you hit performance issues on your specific configuration or want to improve QGIS awesomeness, we provide a unique QGIS support offer at http://qgis.oslandia.com/ thanks to our team of specialists!

Who is behind QGIS at Oslandia ?

You are using QGIS and look for support services to improve your experience and solve problems ? Oslandia is here to help you with our full QGIS editor service range ! Discover our team members below.

You will probably interact first with our pre-sales engineer Bertrand Parpoil. He leads Geographical Information System projects for 15 years for large corporations, public administrations or hi-tech SME. Bertrand will listen to your needs and explore your use cases, to offer you the best set of services.

Régis Haubourg also takes part in the first steps of projects to analyze your usages and improve them. GIS Expert, he knows QGIS by heart and will make the most of its capabilities. As QGIS Community Manager at Oslandia, he is very active in the QGIS community of developers and contributors. He is president of the Francophone OSGeo local chapter ( OSGeo-fr ), QGIS voting member, organizes the French QGIS day conference in Montpellier, and participates to QGIS community meetings. Before joining Oslandia, he led the migration to QGIS and PostGIS at the Adour-Garonne Water Agency, and now guides our clients with their GIS migrations to OpenSource solutions. Régis is also a great asset when working on water, hydrology and other specific thematic subjects.

Loïc Bartoletti develops QGIS, specializing in features corresponding to his fields of interests : network management, topography, urbanism, architecture… We find him contributing to advanced vector editing in QGIS, writing Python plugins, namely for DICT management. Pushing CAD and migrations from CAD tools to GIS and QGIS is one of his major goals. He will develop your custom applications, combining technical expertise and functional competences. When bored, Loïc packages software on FreeBSD.

Vincent Mora is senior developer in Python and C++, as well as PostGIS expert. He has a strong experience in numerical simulation. He likes coupling GIS (PostGIS, QGIS) with 3D numerical computing for risk management or production optimization. Vincent is an official QGIS committer and can directly integrate your needs into the core of the software. He is also GDAL committer and optimizes low-level layers of your applications. Among numerous activities, Vincent serves as lead developer of the development team for Hydra Software, a tool dedicated to unified hydraulics and hydrology modelling and simulation based on QGIS.

Hugo Mercier is an officiel QGIS committer too for several years. He regularly talks in international conferences on PostGIS, QGIS and other OpenSource GIS softwares. He will implement your needs with new QGIS features, develop innovative plugins ( like QGeoloGIS ) and design and build your new custom applications, solving all kind of technological challenges.

Paul Blottière completes our QGIS committers : very active on core development, Paul has refactored the QGIS server component to bring it to an industry-grade quality level. He also designed and implemented the infrastructure allowing to guarantee QGIS server performances. He dedicated himself to QGIS server OGC certification, especially for WMS (1.3). Thanks to this work QGIS is now a reference OGC implementation.

Julien Cabièces recently joined Oslandia, and quickly dived into QGIS : he contributes to the core of this Desktop GIS, on the server component, as well as applications linked to numerical simulation. Coming from a satellite imagery company with industrial applications, he uses his flexibility to answer all your needs. He brings quality and professionalism to your projects, minimizing risks for large production deployments.

You may also meet Vincent Picavet. Oslandia’s founder is a QGIS.org voting member, and is involved in the project’s evolution and the organization of the community.

Aside from these core contributors, all other Oslandia members also master QGIS integrate this tool into their day-to-day projects.

Bertrand, Régis, Loïc, Vincent (x2), Hugo, Paul et Julien are in tune with you and will be happy to work together for your migrations, application development, and all your desires to contribute to the QGIS ecosystem. Do not hesitate to contact us !

Funding for selective masking in QGIS is now complete!

Few months ago, Oslandia launched QGIS lab’s , a place to advertise our new ideas for QGIS, but also a place to help you find co funders to make dreams become reality.

The first initiative is about label selective masking, a feature that will allow us to achieve even more professional rendering for our maps.

Selective masking

 

Thanks to the commitment of the Swiss QGIS user group and local authorities, this work is now funded !

We now can start working hard to deliver you this great feature for QGIS 3.10

Thanks again to our funders

A last word, this is not a classical crowd funding initiative, but a classical contract for each funder.

No more reason not to contribute to free and open source software!

Nouvel outil d’édition des géométries dans QGIS : tronquer/prolonger

Sorry, this entry is only available in French.

Visualization of borehole logs with QGIS

At Oslandia, we have been working on a component based on the QGIS API for the visualization of well and borehole logs.

This component is aiming at displaying data collected vertically along wells dug underground. It mainly focuses on data organized in series of contiguous samples, and is generic enough to be used for both vertical (where the Y axis corresponds to a depth underground) and horizontal data (where the X axis corresponds to time for example). One of the main concerns was to ensure good display performances with an important volume of sample points (usually hundred of thousands sample points).

We have already been working on plot components in the past, but for specific QGIS plugins (both for timeseries and stratigraphic logs) and thought we will put these past experiences to good use by creating a more generic library.

We decided to represent sample points as geometry features in order to be able to reuse the rich symbology engine of QGIS. This allows users to represent their data whatever they like without having to rewrite an entire symbology engine. We also benefit from all the performance optimizations that have been added and polished over the years (on-the-fly geometry simplification for example).

Albeit written in Python, we achieved good display performances. The key trick was to avoid copy of data between the sample points read by QGIS and the Python graphing component. It is achieved thanks to the fact that the PyQGIS API has some functions that respect the buffer protocol.

You can have a look at the following video to see this component integrated in an existing plugin.

Visualization of borehole logs withing QGIS

It is distributed as usual under an open source license and the code repository can be found on GitHub.

Do not hesitate to contact us ( [email protected] ) if you are interested in any enhancements around this component.

New QGIS geometry editing tool: trim/extend

Oslandia is continuing to improve QGIS to offer the draftsman the same experience as with the computer-aided design (CAD) software on the market.
Today we introduce you to the “trim/extend” tool.

As its name suggests, this tool, well known to CAD draftsmen, allows you to trim / shorten or extend segments.

However, where CAD tools impose some limitations – such as using on the end of polyline segments and only on 2D objects – we wanted to go further in QGIS:
– you can modify any segment of a line or polygon geometry and not just its end;
– you can of course modify multi geometries;
– you can hang on to 3D points.

Click to view our demo video.

The tool will be available in version 3.6, but you can use it now in the development version, via the advanced Windows installer for example

This tool was developed thanks to the funding of the Megève Town Hall, which we would like to thank in particular.

It is still possible to improve the tool by offering:

– multiple selection of limits and entities to be modified;
– an option to modify the two selected entities up to their intersection point;
– better support for curved geometries in the future;
– to add topology support when using the tool.

Would you like to participate in its improvement or the development of QGIS?

Need a study or support to move from CAD to GIS?

Do not hesitate to contact us.

Follow us also on twitter or Linkedin to be informed about our new CAD tools in QGIS.

QGIS Server 3 : OGC Certification work for WFS 1.1.0

QGIS Server is an open source OGC data server which uses QGIS engine as backend. It becomes really awesome because a simple desktop qgis project file can be rendered as web services with exactly the same rendering, and without any mapfile or xml coding by hand.

QGIS Server provides a way to serve OGC web services like WMS, WCS, WFS and WMTS resources from a QGIS project, but can also extend services like GetPrint which takes advantage of QGIS’s map composer power to generate high quality PDF outputs.

Since the 3.0.2 version, QGIS Server is certified as an official OGC reference implementation for WMS 1.3.0 and reports are generated in a daily continuous integration to avoid regressions.

 

Thus, the next step was naturally to take a look at the WFS 1.1.0 thanks to the support of the QGIS Grant Program

Side note, this Grant program is made possible thanks to your direct sponsoring and micro-donations to QGIS.org.

TEAM Engine test suite for WFS 1.1.0

We use a tool provided by the OGC Compliance Program to run dedicated tests on the server : Teamengine (Test, Evaluation, And Measurement Engine).

Test suites are available through a web interface. However, for the needs of continuous integration, these tests have to be run without user interaction. In the case of WMS 1.3.0, nothing more easy than using the REST API:

$ curl "http://localhost:8081/teamengine/rest/suites/wms/1.20/run?queryable=queryable&basic=basic&capabilities-url=http://172.17.0.2/qgisserver?REQUEST=GetCapabilities%26SERVICE=WMS%26VERSION=1.3.0%26MAP=/data/teamengine_wms_130.qgs

 

However, the WFS 1.1.0 test suite does not provide a REST API and makes the situation less straightforward. We switched to using TEAM Engine directly from command line:

$ cd te_base
$ ./bin/unix/test.sh -source=wfs/1.1.0/ctl/main.ctl -form=params.xml

The params.xml file allows to configure underlying tests. In this particular case, the GetCapabilities URL of the QGIS Server to test is given.  Results are available thanks to the viewlog.sh shell script:

$ ./bin/unix/viewlog.sh -logdir=te_base/users/root/ -session=s0001
Test wfs:wfs-main type Mandatory (s0001) Failed (InheritedFailure)
   Test wfs:readiness-tests type Mandatory (s0001/d68e38807_1) Failed (InheritedFailure)
      Test ctl:SchematronValidatingParser type Mandatory (s0001/d68e38807_1/d68e588_1) Failed
      Test wfs:basic-main type Mandatory (s0001/d68e38807_1/d68e636_1) Failed (InheritedFailure)
         Test wfs:run-GetCapabilities-basic-cc-GET type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1) Failed (InheritedFailure)
            Test wfs:wfs-1.1.0-Basic-GetCapabilities-tc1 type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1/d68e1095_1) Passed
               Test ctl:assert-xpath type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1/d68e1095_1/d68e1234_1) Passed
            Test wfs:wfs-1.1.0-Basic-GetCapabilities-tc2 type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1/d68e1100_1) Passed
               Test ctl:assert-xpath type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1/d68e1100_1/d68e1305_1) Passed
            Test wfs:wfs-1.1.0-Basic-GetCapabilities-tc3 type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1/d68e1105_1) Passed
               Test ctl:assert-xpath type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1/d68e1105_1/d68e1558_1) Passed
               Test ctl:assert-xpath type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1/d68e1105_1/d68e1582_1) Passed
               Test ctl:assert-xpath type Mandatory (s0001/d68e38807_1/d68e636_1/d68e28810_1/d68e1105_1/d68e1606_1) Passed
...
...

Finally, a Python script has been written to read these logs and generate HTML report easily readable. Thanks to our QGIS-Server-CertifSuite, providing the continuous integration infrastructure with Docker images, these reports are also generated daily.

Bugfix and Conclusion

First results were clear: a lot of work is necessary to have a QGIS Server certified for WFS 1.1.0!

We started fixing the issues one by one:

And now we have a much better support than 6 months ago

However, some work still need to be done to finally obtain the OGC certification for WFS 1.1.0. To be continued!

Please contact us if you want QGIS server to become a reference implementation for all OGC service !

French Ministry in charge of the ecological transition selected Oslandia

Ministère de la Transition Écologique et Solidaire Logo

The French ministry of the ecological transition  selected Oslandia for two of the three packages of its call for tender procedure dedicated to geomatic tools.  We are very proud to dedicate our team to one of the strongest support of geomatics and Open Source in France for the next 2 to 4 years.

First package is dedicated to expert studies covering spatial databases, software, components, protocols, norms and standards in the geomatics fields.

Second package provides support and development for QGIS,  the spatial cartridge PostGIS of PostgreSQL and their components. We are really happy to continue a common work already engaged in the previous contract.

This is again another proof that we face a major tendency of open source investment, where geomatics components are currently among the most dynamic and strongest open source projects. This is also a confirmation that actors are now integrating deeply the economic rationale of open source contribution inside their politics.

“QGZ” – A new default project file format for QGIS

Last year we had the opportunity to implement ‘.QGZ’ as  anew variant of  the QGIS 3 project file format.

This is simply a zipped container for the QGS xml file. We took benefit of that container to store the auxiliary storage database into it – only if users choose that optional format though.

In classical mode, the auxiliary database is saved as a .qgd file  along the xml file.

qgd auxiliary storage file

 

qgz file format saving

When choosing the zipped container, the qgd file falls into the qgz, and this becomes totally transparent for end users. No more issues, you can’t delete it or forget to copy it when sharing project files!

The great news today is that for qgis 3.2, qgz will be the default format!

This will offers many possibilities like embbeding:

  • Resources like fonts, SVG, color ramps, and all styling informations
  • A unified container for off-line editing embedding data into a gpkg format
  • plugins, scripts, processing algorithms and modelers

If you are interested in going further this, please contact us!

Docker images for QGIS

With support from Orange we’ve created Docker images for QGIS. All the material for building and running these images is open-source and freely available on GitHub: https://github.com/Oslandia/docker-qgis.

The docker-qgis repository includes two Docker images: qgis-build and qgis-exec.

The qgis-build image includes all the libraries and tools necessary for building QGIS from source. Building QGIS requires installing a lot of dependencies, so it might not be easy depending on the Operating System you use. The qgis-build image makes it easy and repeatable. The result of a QGIS build is Debian Stretch packages that can be used for building the qgis-exec image, as explained below.

The qgis-exec image includes a runtime environment for QGIS Server. The image makes it easy to deploy and run QGIS Server. It is meant to be be generic and usable in various contexts, and in production. There are two ways to build the qgis-exec image. It can be built from the official QGIS 3 Debian packages (http://qgis.org/debian/), or from local QGIS Debian Stretch packages that were built using the qgis-build image.

We encourage you to go test and use our images! We haven’t pushed the images to the Docker Hub yet, but this is in the plans.

Feel free to contact us on GitHub or by email for any question or request!

QGIS 3.0 has been released

We are very pleased to convey the announcement of the  QGIS 3.0 major release called “Girona”.

The whole QGIS community has been working hard on so many changes for the last two years. This version is a major step in the evolution of QGIS. There are a lot of features, and many changes to the underlying code.

At Oslandia, we pushed some great new features, a lot of bugfixes and made our best to help in synchronizing efforts with the community.

Please note that the installers and binaries are still currently being built for all platforms, Ubuntu and Windows are already there,  and Mac packages are still building.

The ChangeLog and the documentation are still being worked on so please start testing that brand new version and let’s make it stronger and stronger together. The more contributors, the better!

While QGIS 3.0 represent a lot of work, note that this version is not a “Long Term Release” and may not be as stable as required for production work.

We would like to thank all the contributors who helped making QGIS 3 a reality.

Oslandia contributors should acknowledged too : Hugo Mercier, Paul Blottière, Régis Haubourg, Vincent Mora and Loïc Bartoletti.

We also want to thank some those who supported directly important features of QGIS3 :

Orange

The QWAT / QGEP organization

The French Ministry for an Ecological and Inclusive Transition

ESG

and also Grenoble Alpes Métropole

QGIS 3.0 has been released

We are very pleased to convey the announcement of the  QGIS 3.0 major release called “Girona”.

The whole QGIS community has been working hard on so many changes for the last two years. This version is a major step in the evolution of QGIS. There are a lot of features, and many changes to the underlying code.

At Oslandia, we pushed some great new features, a lot of bugfixes and made our best to help in synchronizing efforts with the community.

Please note that the installers and binaries are still currently being built for all platforms, Ubuntu and Windows are already there,  and Mac packages are still building.

The ChangeLog and the documentation are still being worked on so please start testing that brand new version and let’s make it stronger and stronger together. The more contributors, the better!

While QGIS 3.0 represent a lot of work, note that this version is not a “Long Term Release” and may not be as stable as required for production work.

We would like to thank all the contributors who helped making QGIS 3 a reality.

Oslandia contributors should acknowledged too : Hugo Mercier, Paul Blottière, Régis Haubourg, Vincent Mora and Loïc Bartoletti.

We also want to thank some those who supported directly important features of QGIS3 :

Orange

The QWAT / QGEP organization

The French Ministry for an Ecological and Inclusive Transition

ESG

and also Grenoble Alpes Métropole

QGIS 3 compiling on Windows

As the Oslandia team work exclusively on GNU/Linux, the exercise of compiling QGIS 3 on Windows 8 is not an everyday’s task :). So we decided to share our experience, we bet that will help some of you.

Cygwin

The first step is to download Cygwin and to install it in the directory C:\cygwin (instead of the default C:\cygwin64). During the installation, select the lynx package:

 

Once installed, you have to click on the Cygwin64 Terminal icon newly created on your desktop:

Then, we’re able to install dependencies and download some other installers:

[pastacode lang=”bash” manual=”%24%20cd%20%2Fcygdrive%2Fc%2FUsers%2Fhenri%2FDownloads%0A%24%20lynx%20-source%20rawgit.com%2Ftranscode-open%2Fapt-cyg%2Fmaster%2Fapt-cyg%20%3E%20apt-cyg%0A%24%20install%20apt-cyg%20%2Fbin%0A%24%20apt-cyg%20install%20wget%20git%20flex%20bison%0A%24%20wget%20http%3A%2F%2Fdownload.microsoft.com%2Fdownload%2FD%2F2%2F3%2FD23F4D0F-BA2D-4600-8725-6CCECEA05196%2Fvs_community_ENU.exe%0A%24%20chmod%20u%2Bx%20vs_community_ENU.exe%0A%24%20wget%20https%3A%2F%2Fcmake.org%2Ffiles%2Fv3.7%2Fcmake-3.7.2-win64-x64.msi%0A%24%20wget%20http%3A%2F%2Fdownload.osgeo.org%2Fosgeo4w%2Fosgeo4w-setup-x86_64.exe%0A%24%20chmod%20u%2Bx%20osgeo4w-setup-x86_64.exe” message=”” highlight=”” provider=”manual”/]

CMake

The next step is to install CMake. To do that, double clic on the file cmake-3.7.2-win64-x64.msi previously downloaded with wget. You should choose the next options during the installation:

 

Visual Studio

Then, we have to install Visual Studio and C++ tools. Double click on the vs_community_ENU.exe file and select the Custom installation. On the next page, you have to select Visual C++ chekbox:

 

 

OSGeo4W

In order to compile QGIS, some dependencies provided by the OSGeo4W installer are required. Double click on osgeo4w-setup-x86_64.exe and select the Advanced Install mode. Then, select the next packages:

  •  expat
  • fcgi
  • gdal
  • grass
  • gsl-devel
  • iconv
  • libzip-devel
  • libspatialindex-devel
  • pyqt5
  • python3-devel
  • python3-qscintilla
  • python3-nose2
  • python3-future
  • python3-pyyaml
  • python3-mock
  • python3-six
  • qca-qt5-devel
  • qca-qt5-libs
  • qscintilla-qt5
  • qt5-devel
  • qt5-libs-debug
  • qtwebkit-qt5-devel
  • qtwebkit-qt5-libs-debug
  • qwt-devel-qt5
  • sip-qt5
  • spatialite
  • oci
  • qtkeychain

QGIS

To start this last step, we have to create a file C:\OSGeo4W\OSGeo4W-dev.bat containing something like:

[pastacode lang=”bash” manual=”%40echo%20off%20%0Aset%20OSGEO4W_ROOT%3DC%3A%5COSGeo4W64%0Acall%20%22%25OSGEO4W_ROOT%25%5Cbin%5Co4w_env.bat%22%20%0Acall%20%22%25OSGEO4W_ROOT%25%5Cbin%5Cqt5_env.bat%22%20%0Acall%20%22%25OSGEO4W_ROOT%25%5Cbin%5Cpy3_env.bat%22%20%0Aset%20VS140COMNTOOLS%3D%25PROGRAMFILES(x86)%25%5CMicrosoft%20Visual%20Studio%2014.0%5CCommon7%5CTools%5C%20%0Acall%20%22%25PROGRAMFILES(x86)%25%5CMicrosoft%20Visual%20Studio%2014.0%5CVC%5Cvcvarsall.bat%22%20amd64%20%0Aset%20INCLUDE%3D%25INCLUDE%25%3B%25PROGRAMFILES(x86)%25%5CMicrosoft%20SDKs%5CWindows%5Cv7.1A%5Cinclude%20%0Aset%20LIB%3D%25LIB%25%3B%25PROGRAMFILES(x86)%25%5CMicrosoft%20SDKs%5CWindows%5Cv7.1A%5Clib%20%0Apath%20%25PATH%25%3B%25PROGRAMFILES%25%5CCMake%5Cbin%3Bc%3A%5Ccygwin%5Cbin%20%0A%40set%20GRASS_PREFIX%3D%22%25OSGEO4W_ROOT%25%5Capps%5Cgrass%5Cgrass-7.2.1%20%0A%40set%20INCLUDE%3D%25INCLUDE%25%3B%25OSGEO4W_ROOT%25%5Cinclude%20%0A%40set%20LIB%3D%25LIB%25%3B%25OSGEO4W_ROOT%25%5Clib%3B%25OSGEO4W_ROOT%25%5Clib%20%0A%0A%40cmd%20″ message=”” highlight=”” provider=”manual”/]

According to your environment, some variables should probably be adapted. Then in the Cygwin terminal:

[pastacode lang=”bash” manual=”%24%20cd%20C%3A%5C%0A%24%20git%20clone%20git%3A%2F%2Fgithub.com%2Fqgis%2FQGIS.git%0A%24%20.%2FOSGeo4W-dev.bat%0A%3E%20cd%20QGIS%2Fms-windows%2Fosgeo4w” message=”” highlight=”” provider=”manual”/]

In this directory, you have to edit the file package-nightly.cmd to replace:

[pastacode lang=”bash” manual=”cmake%20-G%20Ninja%20%5E” message=”” highlight=”” provider=”manual”/]

by:

[pastacode lang=”bash” manual=”cmake%20-G%20%22Visual%20Studio%2014%202015%20Win64%22%20%5E” message=”” highlight=”” provider=”manual”/]

Moreover, we had to update the environment variable SETUAPI_LIBRARY according to the current position of the Windows Kits file SetupAPI.Lib:

[pastacode lang=”bash” manual=”set%20SETUPAPI_LIBRARY%3DC%3A%5CProgram%20Files%20(x86)%5CWindows%20Kits%5C8.1%5CLib%5Cwinv6.3%5Cum%5Cx64%5CSetupAPI.Lib” message=”” highlight=”” provider=”manual”/]

And finally, we just have to compile with the next command:

[pastacode lang=”markup” manual=”%3E%20package-nightly.cmd%202.99.0%201%20qgis-dev%20x86_64″ message=”” highlight=”” provider=”manual”/]

Victory!

And see you soon for the generation of OSGEO4W packages 😉

Source

https://github.com/qgis/QGIS/blob/ab859c9bdf8a529df9805ff54e7250921a74d877/doc/msvc.t2t

 

 

QGIS 3 compiling on Windows

As the Oslandia team work exclusively on GNU/Linux, the exercise of compiling QGIS 3 on Windows 8 is not an everyday’s task :). So we decided to share our experience, we bet that will help some of you.

Cygwin

The first step is to download Cygwin and to install it in the directory C:\cygwin (instead of the default C:\cygwin64). During the installation, select the lynx package:

 

Once installed, you have to click on the Cygwin64 Terminal icon newly created on your desktop:

Then, we’re able to install dependencies and download some other installers:

[pastacode lang=”bash” manual=”%24%20cd%20%2Fcygdrive%2Fc%2FUsers%2Fhenri%2FDownloads%0A%24%20lynx%20-source%20rawgit.com%2Ftranscode-open%2Fapt-cyg%2Fmaster%2Fapt-cyg%20%3E%20apt-cyg%0A%24%20install%20apt-cyg%20%2Fbin%0A%24%20apt-cyg%20install%20wget%20git%20flex%20bison%0A%24%20wget%20http%3A%2F%2Fdownload.microsoft.com%2Fdownload%2FD%2F2%2F3%2FD23F4D0F-BA2D-4600-8725-6CCECEA05196%2Fvs_community_ENU.exe%0A%24%20chmod%20u%2Bx%20vs_community_ENU.exe%0A%24%20wget%20https%3A%2F%2Fcmake.org%2Ffiles%2Fv3.7%2Fcmake-3.7.2-win64-x64.msi%0A%24%20wget%20http%3A%2F%2Fdownload.osgeo.org%2Fosgeo4w%2Fosgeo4w-setup-x86_64.exe%0A%24%20chmod%20u%2Bx%20osgeo4w-setup-x86_64.exe” message=”” highlight=”” provider=”manual”/]

CMake

The next step is to install CMake. To do that, double clic on the file cmake-3.7.2-win64-x64.msi previously downloaded with wget. You should choose the next options during the installation:

 

Visual Studio

Then, we have to install Visual Studio and C++ tools. Double click on the vs_community_ENU.exe file and select the Custom installation. On the next page, you have to select Visual C++ chekbox:

 

 

OSGeo4W

In order to compile QGIS, some dependencies provided by the OSGeo4W installer are required. Double click on osgeo4w-setup-x86_64.exe and select the Advanced Install mode. Then, select the next packages:

  •  expat
  • fcgi
  • gdal
  • grass
  • gsl-devel
  • iconv
  • libzip-devel
  • libspatialindex-devel
  • pyqt5
  • python3-devel
  • python3-qscintilla
  • python3-nose2
  • python3-future
  • python3-pyyaml
  • python3-mock
  • python3-six
  • qca-qt5-devel
  • qca-qt5-libs
  • qscintilla-qt5
  • qt5-devel
  • qt5-libs-debug
  • qtwebkit-qt5-devel
  • qtwebkit-qt5-libs-debug
  • qwt-devel-qt5
  • sip-qt5
  • spatialite
  • oci
  • qtkeychain

QGIS

To start this last step, we have to create a file C:\OSGeo4W\OSGeo4W-dev.bat containing something like:

[pastacode lang=”bash” manual=”%40echo%20off%20%0Aset%20OSGEO4W_ROOT%3DC%3A%5COSGeo4W64%0Acall%20%22%25OSGEO4W_ROOT%25%5Cbin%5Co4w_env.bat%22%20%0Acall%20%22%25OSGEO4W_ROOT%25%5Cbin%5Cqt5_env.bat%22%20%0Acall%20%22%25OSGEO4W_ROOT%25%5Cbin%5Cpy3_env.bat%22%20%0Aset%20VS140COMNTOOLS%3D%25PROGRAMFILES(x86)%25%5CMicrosoft%20Visual%20Studio%2014.0%5CCommon7%5CTools%5C%20%0Acall%20%22%25PROGRAMFILES(x86)%25%5CMicrosoft%20Visual%20Studio%2014.0%5CVC%5Cvcvarsall.bat%22%20amd64%20%0Aset%20INCLUDE%3D%25INCLUDE%25%3B%25PROGRAMFILES(x86)%25%5CMicrosoft%20SDKs%5CWindows%5Cv7.1A%5Cinclude%20%0Aset%20LIB%3D%25LIB%25%3B%25PROGRAMFILES(x86)%25%5CMicrosoft%20SDKs%5CWindows%5Cv7.1A%5Clib%20%0Apath%20%25PATH%25%3B%25PROGRAMFILES%25%5CCMake%5Cbin%3Bc%3A%5Ccygwin%5Cbin%20%0A%40set%20GRASS_PREFIX%3D%22%25OSGEO4W_ROOT%25%5Capps%5Cgrass%5Cgrass-7.2.1%20%0A%40set%20INCLUDE%3D%25INCLUDE%25%3B%25OSGEO4W_ROOT%25%5Cinclude%20%0A%40set%20LIB%3D%25LIB%25%3B%25OSGEO4W_ROOT%25%5Clib%3B%25OSGEO4W_ROOT%25%5Clib%20%0A%0A%40cmd%20″ message=”” highlight=”” provider=”manual”/]

According to your environment, some variables should probably be adapted. Then in the Cygwin terminal:

[pastacode lang=”bash” manual=”%24%20cd%20C%3A%5C%0A%24%20git%20clone%20git%3A%2F%2Fgithub.com%2Fqgis%2FQGIS.git%0A%24%20.%2FOSGeo4W-dev.bat%0A%3E%20cd%20QGIS%2Fms-windows%2Fosgeo4w” message=”” highlight=”” provider=”manual”/]

In this directory, you have to edit the file package-nightly.cmd to replace:

[pastacode lang=”bash” manual=”cmake%20-G%20Ninja%20%5E” message=”” highlight=”” provider=”manual”/]

by:

[pastacode lang=”bash” manual=”cmake%20-G%20%22Visual%20Studio%2014%202015%20Win64%22%20%5E” message=”” highlight=”” provider=”manual”/]

Moreover, we had to update the environment variable SETUAPI_LIBRARY according to the current position of the Windows Kits file SetupAPI.Lib:

[pastacode lang=”bash” manual=”set%20SETUPAPI_LIBRARY%3DC%3A%5CProgram%20Files%20(x86)%5CWindows%20Kits%5C8.1%5CLib%5Cwinv6.3%5Cum%5Cx64%5CSetupAPI.Lib” message=”” highlight=”” provider=”manual”/]

And finally, we just have to compile with the next command:

[pastacode lang=”markup” manual=”%3E%20package-nightly.cmd%202.99.0%201%20qgis-dev%20x86_64″ message=”” highlight=”” provider=”manual”/]

Victory!

And see you soon for the generation of OSGEO4W packages 😉

Source

https://github.com/qgis/QGIS/blob/ab859c9bdf8a529df9805ff54e7250921a74d877/doc/msvc.t2t

 

 

Auxiliary Storage support in QGIS 3

For those who know how powerful QGIS can be using data defined widgets and expressions almost anywhere in styling and labeling settings, it remains today quite complex to store custom data.

For instance, moving a simple label using the label toolbar is not straightforward, that wonderful toolbar remains desperately greyed-out for manual labeling tweaks

…unless you do the following:

  • Set your vector layer editable (yes, it’s not possible with readonly data)
  • Add two columns in your data
  • Link the X property position to a column and the Y position to another

 

the Move Label map tool becomes available and ready to be used (while your layer is editable). Then, if you move a label, the underlying data is modified to store the position. But what happened if you want to fully use the Change Label map tool (color, size, style, and so on)?

 

Well… You just have to add a new column for each property you want to manage. No need to tell you that it’s not very convenient to use or even impossible when your data administrator has set your data in readonly mode…

A plugin, made some years ago named EasyCustomLabeling was made to address that issue. But it kept being full of caveats, like a dependency to another plugin (Memory layer saver) for persistence, or a full copy of the layer to label inside a memory layer which indeed led to loose synchronisation with the source layer.

Two years ago, the French Agence de l’eau Adour Garonne (a water basin agency) and the Ministry in charge of Ecology asked Oslandia to think out QGIS Enhancement proposals to port that plugin into QGIS core, among a few other things like labeling connectors or curved labels enhancements.

Those QEPs were accepted and we could work on the real implementation, so here we are, Auxiliary storage has now landed in master!

How

The aim of auxiliary storage is to propose a more integrated solution to manage these data defined properties :

  • Easy to use (one click)
  • Transparent for the user (map tools always available by default when labeling is activated)
  • Do not update the underlying data (it should work even when the layer is not editable)
  • Keep in sync with the datasource (as much as possible)
  • Store this data along or inside the project file

As said above, thanks to the Auxiliary Storage mechanism, map tools like Move Label, Rotate Label or Change Label are available by default. Then, when the user select the map tool to move a label and click for the first time on the map, a simple question is asked allowing to select a primary key :

Primary key choice dialog – (YES, you NEED a primary key for any data management)

From that moment on, a hidden table is transparently created to store all data defined values (positions, rotations, …) and joined to the original layer thanks to the primary key previously selected. When you move a label, the corresponding property is automatically created in the auxiliary layer. This way, the original data is not modified but only the joined auxiliary layer!

A new tab has been added in vector layer properties to manage the Auxiliary Storage mechanism. You can retrieve, clean up, export or create new properties from there :

Where the auxiliary data is really saved between projects?

We end up in using a light SQLite database which, by default, is just 8 Ko! When you save your project with the usual extension .qgs, the SQLite database is saved at the same location but with a different extension : .qgd.

Two thoughts with that choice: 

  • “Hey, I would like to store geometries, why no spatialite instead? “

Good point. We tried that at start in fact. But spatialite database initializing process using QGIS spatialite provider was found too long, really long. And a raw spatialite table weight about 4 Mo, because of the huge spatial reference system table, the numerous spatial functions and metadata tables. We chose to fall back onto using sqlite through OGR provider and it proved to be fast and stable enough. If some day, we achieve in merging spatialite provider and GDAL-OGR spatialite provider, with options to only create necessary SRS and functions, that would open news possibilities, like storing spatial auxiliary data.

  • “Does that mean that when you want to move/share a QGIS project, you have to manually manage these 2 files to keep them in the same location?!”

True, and dangerous isn’t it? Users often forgot auxiliary files with EasyCustomLabeling plugin.  Hence, we created a new format allowing to zip several files : .qgz.  Using that format, the SQLite database project.qgd and the regular project.qgs file will be embedded in a single project.zip file. WIN!!

Changing the project file format so that it can embed, data, fonts, svg was a long standing feature. So now we have a format available for self hosted QGIS project. Plugins like offline editing, Qconsolidate and other similar that aim at making it easy to export a portable GIS database could take profit of that new storage container.

Now, some work remains to add labeling connectors capabilities,  allow user to draw labeling paths by hand. If you’re interested in making this happen, please contact us!

 

 

More information

A full video showing auxiliary storage capabilities:

 

QEP: https://github.com/qgis/QGIS-Enhancement-Proposals/issues/27

PR New Zip format: https://github.com/qgis/QGIS/pull/4845

PR Editable Joined layers: https://github.com/qgis/QGIS/pull/4913

PR Auxiliary Storage: https://github.com/qgis/QGIS/pull/5086

Auxiliary Storage support in QGIS 3

For those who know how powerful QGIS can be using data defined widgets and expressions almost anywhere in styling and labeling settings, it remains today quite complex to store custom data.

For instance, moving a simple label using the label toolbar is not straightforward, that wonderful toolbar remains desperately greyed-out for manual labeling tweaks

…unless you do the following:

  • Set your vector layer editable (yes, it’s not possible with readonly data)
  • Add two columns in your data
  • Link the X property position to a column and the Y position to another

 

the Move Label map tool becomes available and ready to be used (while your layer is editable). Then, if you move a label, the underlying data is modified to store the position. But what happened if you want to fully use the Change Label map tool (color, size, style, and so on)?

 

Well… You just have to add a new column for each property you want to manage. No need to tell you that it’s not very convenient to use or even impossible when your data administrator has set your data in readonly mode…

A plugin, made some years ago named EasyCustomLabeling was made to address that issue. But it kept being full of caveats, like a dependency to another plugin (Memory layer saver) for persistence, or a full copy of the layer to label inside a memory layer which indeed led to loose synchronisation with the source layer.

Two years ago, the French Agence de l’eau Adour Garonne (a water basin agency) and the Ministry in charge of Ecology asked Oslandia to think out QGIS Enhancement proposals to port that plugin into QGIS core, among a few other things like labeling connectors or curved labels enhancements.

Those QEPs were accepted and we could work on the real implementation, so here we are, Auxiliary storage has now landed in master!

How

The aim of auxiliary storage is to propose a more integrated solution to manage these data defined properties :

  • Easy to use (one click)
  • Transparent for the user (map tools always available by default when labeling is activated)
  • Do not update the underlying data (it should work even when the layer is not editable)
  • Keep in sync with the datasource (as much as possible)
  • Store this data along or inside the project file

As said above, thanks to the Auxiliary Storage mechanism, map tools like Move Label, Rotate Label or Change Label are available by default. Then, when the user select the map tool to move a label and click for the first time on the map, a simple question is asked allowing to select a primary key :

Primary key choice dialog – (YES, you NEED a primary key for any data management)

From that moment on, a hidden table is transparently created to store all data defined values (positions, rotations, …) and joined to the original layer thanks to the primary key previously selected. When you move a label, the corresponding property is automatically created in the auxiliary layer. This way, the original data is not modified but only the joined auxiliary layer!

A new tab has been added in vector layer properties to manage the Auxiliary Storage mechanism. You can retrieve, clean up, export or create new properties from there :

Where the auxiliary data is really saved between projects?

We end up in using a light SQLite database which, by default, is just 8 Ko! When you save your project with the usual extension .qgs, the SQLite database is saved at the same location but with a different extension : .qgd.

Two thoughts with that choice: 

  • “Hey, I would like to store geometries, why no spatialite instead? “

Good point. We tried that at start in fact. But spatialite database initializing process using QGIS spatialite provider was found too long, really long. And a raw spatialite table weight about 4 Mo, because of the huge spatial reference system table, the numerous spatial functions and metadata tables. We chose to fall back onto using sqlite through OGR provider and it proved to be fast and stable enough. If some day, we achieve in merging spatialite provider and GDAL-OGR spatialite provider, with options to only create necessary SRS and functions, that would open news possibilities, like storing spatial auxiliary data.

  • “Does that mean that when you want to move/share a QGIS project, you have to manually manage these 2 files to keep them in the same location?!”

True, and dangerous isn’t it? Users often forgot auxiliary files with EasyCustomLabeling plugin.  Hence, we created a new format allowing to zip several files : .qgz.  Using that format, the SQLite database project.qgd and the regular project.qgs file will be embedded in a single project.zip file. WIN!!

Changing the project file format so that it can embed, data, fonts, svg was a long standing feature. So now we have a format available for self hosted QGIS project. Plugins like offline editing, Qconsolidate and other similar that aim at making it easy to export a portable GIS database could take profit of that new storage container.

Now, some work remains to add labeling connectors capabilities,  allow user to draw labeling paths by hand. If you’re interested in making this happen, please contact us!

 

 

More information

A full video showing auxiliary storage capabilities:

 

QEP: https://github.com/qgis/QGIS-Enhancement-Proposals/issues/27

PR New Zip format: https://github.com/qgis/QGIS/pull/4845

PR Editable Joined layers: https://github.com/qgis/QGIS/pull/4913

PR Auxiliary Storage: https://github.com/qgis/QGIS/pull/5086

Oslandia is baking some awesome QGIS 3 new features

QGIS 3.0 is now getting closer and closer, it’s the right moment to write about some major refactor and new features we have been baking at Oslandia.

A quick word about the release calendar, you probably felt like QGIS 3 freeze was expected for the end of August, didn’t you?

In fact, we have so many new major changes in the queue that the steering committee (PSC), advised by the core developers, decided to push twice the release date up up to the 27 of October. Release date has not be been pushed (yet).

At Oslandia we got involved in a dark list of hidden features of QGIS3.

They mostly aren’t easy to advertised visually, but you’ll appreciate them for sure!

  • Add  capabilities to store data in the project
    • add a new .qgz zipped file format container
    • have editable joins, with upsert capabilities (Insert Or Update)
    • Transparently store  and maintain in sync data in a sqlite database. Now custom labeling is pretty easy!
  • Coordinating work and tests on new node tool for data editing
  • Improving Z / m handling in edit tools and layer creation dialogs
  • Ticket reviewing and cleaning

Next articles will describe some of those tasks soon.

This work was a great opportunity to ramp up a new talented developer with commit rights on the repository! Welcome and congratulations to Paul our new core committer !

All this was possible with the support of many actors, but also thanks to the fundings of QGIS.org via Grant Applications or direct funding of QGIS server!

A last word, please help us in testing QGIS3, it’s the perfect moment to stress it, bugfix period is about to start !

 

 

 

Refresh your maps FROM postgreSQL !

Continuing our love story with PostgreSQL and QGIS, we asked QGIS.org a grant application during early 2017 spring.

The idea was to take benefit of very advanced PostgreSQL features, that probably never were used in a Desktop GIS client before.

Today, let’s see what we can do with the PostgreSQL NOTIFY feature!

Ever dreamt of being able to trigger things from outside QGIS? Ever wanted a magic stick to trigger actions in some clients from a database action?

X All The Y Meme | REFRESH QGIS FROM THE DATABASE !!! | image tagged in memes,x all the y | made w/ Imgflip meme maker

 

NOTIFY is a PostgreSQL specific feature allowing to generate notifications on a channel and optionally send a message — a payload in PG’s dialect .

In short, from within a transaction, we can raise a signal in a PostgreSQL queue and listen to it from a client.

In action

We hardcoded a channel named “qgis” and made QGIS able to LISTEN to NOTIFY events and transform them into Qt’s signals. The signals are connected to layer refresh when you switch on this rendering option.

Optionnally, adding a message filter will only redraw the layer for some specific events.

This mechanism is really versatile and we now can imagine many possibilities, maybe like trigger a notification message to your users from the database, interact with plugins, or even code a chat between users of the same database  (ok, this is stupid) !

 

More than just refresh layers?

The first implementation we chose was to trigger a layer refresh because we believe this is a good way for users to discover this new feature.

But QGIS rocks hey, doing crazy things for limited uses is not the way.

Thanks to feedback on the Pull Request, we added the possibility to trigger layer actions on notification.

That should be pretty versatile since you can do almost anything with those actions now.

Caveats

QGIS will open a permanent connection to PostgreSQL to watch the notify signals. Please keep that in mind if you have several clients and a limited number of connections.

Notify signals are only transmitted with the transaction, so when the COMMIT is raised. So be aware that this might not help you if users are inside an edit session.

QGIS has a lot of different caches, for attribute table for instance. We currently have no specific way to invalidate a specific cache, and then order QGIS to refresh it’s attribute table.

There is no way in PG to list all channels of a database session, that’s why we couldn’t propose a combobox list of available signals in the renderer option dialog. Anyway, to avoid too many issues, we decided to hardcode the channel name in QGIS with the name “qgis”. If this is somehow not enough for your needs, please contact us!

Conclusion

The github pull request is here : https://github.com/qgis/QGIS/pull/5179

We are convinced this would be really useful for real time application, let us know if that makes some bells ring on your side!

More to come soon, stay tuned!

 

 

Undo Redo stack is back QGIS Transaction groups

Let’s keep on looking at what we did in QGIS.org grant application of early 2017 spring.

At Oslandia, we use a lot the transaction groups option of QGIS. It was an experimental feature in QGIS 2.X allowing to open only one common Postgres transaction for all layers sharing the same connection string.

Transaction group option

When activated, that option will bring many killer features:

  • Users can switch all the layers in edit mode at once. A real time saver.
  • Every INSERT, UPDATE or DELETE is forwarded immediately to the database, which is nice for:
    • Evaluating on the fly if database constraints are satisfied or not. Without transaction groups this is only done when saving the edits and this can be frustrating to create dozens of features and having one of them rejected because of a foreign key constraint…
    • Having triggers evaluated on the fly.  QGIS is so powerful when dealing with “thick database” concepts that I would never go back to a pure GIS ignoring how powerful databases can be !
    • Playing with QgsTransaction.ExecuteSQL allows to trigger stored procedures in PostgreSQL in a beautiful API style interface. Something like
SELECT invert_pipe_direction('pipe1');
  • However, the implementation was flagged “experimental” because some caveats where still causing issues:
    • Committing on the fly was breaking the logic of the undo/redo stack. So there was no way to do a local edit. No Ctrl+Z!  The only way to rollback was to stop the edit session and loose all the work. Ouch.. Bad!
    • Playing with ExecuteSQL did not dirty the QGIS edit buffer. So, if during an edit session no edit action was made using QGIS native tools, there was no clean way to activate the “save edits” icon.
    • When having some failures in the triggers, QGIS may loose DB connection and thus create a silent ROLLBACK.

We decided to try to restore the undo/redo stack by saving the history edits in PostgreSQL SAVEPOINTS and see if we could restore the original feature in QGIS.

And.. it worked!

Let’s see that in action:

 

Potential caveats ?

At start, we worried about how heavy all those savepoints would be for the database. It turns out that maybe for really massive geometries, and heavy editing sessions, this could start to weight a bit, but honestly far away from PostgreSQL capabilities.

 

Up to now, we didn’t really find any issue with that..

And we didn’t address the silent ROLLBACK that occurs sometimes, because it is generated by buggy stored procedures, easy to solve.

Some new ideas came to us when working in that area. For instance, if a transaction locks a feature, QGIS just… wait for the lock to be released. I think we should find a way to advertise those locks to the users, that would be great! If you’re interested in making that happen, please contact us.

 

More to come soon, stay tuned!

 

 

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