Here’s a cool trick which you can do in QGIS 2.0. It builds on two new features introduced in version 2.0 – atlas prints and html labels.

Atlas prints (previously available as a plugin, now integrated into QGIS core) were developed by Oslandia, and allow you to create data driven map layouts from a specified coverage layer. You can read more about them here.

Another new feature in QGIS 2.0 is the ability to render composer labels as html (courtesy of Olivier Dalang). This allows all kinds of fantastic effects, such as formatting text in the middle of a label (using <b>, <i>, and <font> tags) or creating labels which contain HTML tables. You can even use CSS stylesheets and rules to format the HTML! I’ve been told JavaScript also works inside the labels, but I’ve yet to try this out.

You can combine these two new features for some great tricks. Let’s say we’d like to create a set of maps of local councils, and we want each map to have a watermarked logo of the council on it. For this example I’ve created a basic basemap of Victorian councils, and I’ve downloaded all the council logos (in a variety of formats) to a local folder. Next, I’ll add an extra column to the council layer containing the name of the logo image:

Then, we’ll throw together a simple composition containing the map and set it up as an atlas print:

Now for the fun bit. I’ll add a label item to the composer, set it to “Render as HTML”, and insert some specially-crafted html:

For copy/paste purposes here’s the label contents again:

<style>
* {margin: 0px; padding: 0px}
</style>
<img src="file:///home/nyall/GIS/council_logos/[% "logo" %]"
style="width: auto; height: 100%; display: block; margin: 0px 0px 0px auto;" />

There’s a couple of things to note here. First, the magic happens in the image’s src attribute (“file:///home/nyall/GIS/council_logos/[% "logo" %]“). When the composer is exported, QGIS will replace the [% "logo" %] part with the contents of the logo field for each row in the councils table. This means the image source will then point to the local copy of the council’s logo, eg “file:///home/nyall/GIS/council_logos/glen_eira.jpg” for the first row.

Secondly, I’ve styled the image with the css:

width: auto; height: 100%; display: block;

This allows the image to resize to 100% of the height of the label while maintaining its correct aspect ratio. I’ve also added the rule

margin: 0px 0px 0px auto;

to force the image to right align within the html label. This ensures that all the watermarked logos will appear in a consistent size and position for each map.

Lastly, I’ll remove the label’s frame and background by unchecking these options, then set its transparency to 80% under the new “Rendering” section:

Ok, we’re all done. Now, when I select Composer -> “Export as Image”, we’ll get a lovely set of council maps complete with watermarked council logo!

There we go — all ready for print, with no manipulation in external programs required at all!

Bonus post-credits section

Here’s a kicker — the linked images don’t need to be local. That means you can even piggy-back off an existing web service to generate an image on the fly! Let’s say you were asked to add QR codes to your maps to link directly to the council website. All it takes is adding a new column to the table, then modifying the image src to read:

src="http://qrfree.kaywa.com/?l=1&s=8&d=[% "url" %]"

Now when we export the maps we’ll also get a QR image generated on the fly and inserted into the layout!

Combining HTML labels and atlas prints in this way is extremely powerful. This example is just touching the tip of the iceberg – I’m keen to see what the community can do with this when QGIS 2.0 is released!

Seems this is a good day for QGIS Oracle users. According this commit made by Jürgen QGIS now has built-in Oracle support. Win!

Native Oracle support can now see QGIS being opened up to a wider user base yet again. A large user base normally means more people willing to sponsor awesome new features and bug fixes. Having seen the growth in the user base from having native MS SQL Server 2008+ support I can imagine what it will be like with Oracle.

The list of formats QGIS can open and edit is getting larger and larger with each release. Is there a future for vendor lock in? I can’t see it.

Standard disclaimer about latest dev build and new features :)

Filed under: Open Source, qgis Tagged: FOSSGIS, gis, Open Source, oracle, osgeo, qgis, qgis-editing, Quantum GIS

A quick update from the QGIS documentation team today on the mailing list. The QGIS 1.8 manual is now available in HTML and PDF form.

HTML manual can be found at:
http://docs.qgis.org/html/en/docs/user_manual/index.html

PDF manual at:
http://docs.qgis.org/pdf/QGIS-1.8-UserGuide-en.pdf

This has been part of an ongoing effort from the documentation team since before the 1.8 release to bring our all our documentation into reStructedText rather then LaTeX. Moving to reStructedText allows quicker updates and a larger range of final output formats.

I would like to thank everyone who has been involved in this process as I know what a grueling process updating documentation can be.

Community notice

Just remember you don’t have to be a programmer to contribute to an open source project. If you think you could contribute to the updating of the QGIS documentation please contact the team on the mailing list.

Filed under: Open Source, qgis Tagged: FOSSGIS, gis, Open Source, osgeo, qgis, Quantum GIS

A second release candidate of GRASS GIS 6.4.3 with improvements and stability fixes is now available.

Source code:
 http://grass.osgeo.org/grass64/source/
 http://grass.osgeo.org/grass64/source/grass-6.4.3RC2.tar.gz

Selected Binaries (more will be published)

• http://grass.osgeo.org/grass64/binary/mswindows/native/WinGRASS-6.4.3RC2-1-Setup.exe
• http://trac.osgeo.org/osgeo4w/wiki/pkg-grass
• http://www.public.asu.edu/~cmbarton/files/grass_mac/OSX10.6-snowleopard/GRASS-6.4.3RC2.pkg.zip
• http://download.opensuse.org/repositories/home:/tzotsos:/Application:/Geo/

To get the RC2 source code from SVN:
 svn checkout https://svn.osgeo.org/grass/grass/tags/release_20121218_grass_6_4_3RC2/

An announcement has been drafted at
 http://trac.osgeo.org/grass/wiki/Release/6.4.3RC2-News

Key improvements of the GRASS 6.4.3 release include some new functionality (image processing tools), major speedup for some vector modules, fixes for the wxPython based portable graphical interface, improvements for the Python API, enhanced portability for MS-Windows (native support), and more translations.

Release candidate management at
 http://trac.osgeo.org/grass/wiki/Grass6Planning

Please join us in testing this release candidate for the final release.

Thanks to all contributors!

The easiest way install Python libraries is to use easy_install and pip.  easy_install and pip are package managers for Python. From the easy_install page:

Easy Install is a python module (easy_install) bundled with setuptools that lets you automatically download, build, install, and manage Python packages.

and from the pip page:

pip is a tool for installing and managing Python packages, such as those found in the Python Package Index. It’s a replacement for easy_install.

To get easy_install you need to install Python setuptools and you are good to go. Sounds easy!  However the setuptools installer assumes that you have the normal standalone Python installed which writes it’s install location to the registry, and when you run the installer it will say that it can’t find Python on the system.  What the!?

If you have installed QGIS, or any other tool from the OSGeo4W install, you will see that OSGeo4W bundles its own version of Python in: C:\OSGeo4W\apps\python27. This is the Python that is used when calling python in the OSGeo4W shell.  It seems someone on the OSGeo wiki has made a bootstrapped installer for setuptools that will install setuptools and easy_install into the  C:\OSGeo4W\apps\python27 folder for you.

Steps to take

• Download ez_setup.py
• Run python ez_setup.py in your OSGeo4W shell
• Done!

To install a package with easy_install just use:

easy_install {packagename}

I wanted to have bottle and flask installed:

easy_install bottle

which gives you something like:

Searching for bottle
Reading http://pypi.python.org/simple/bottle/
Reading http://bottle.paws.de/
Reading http://github.com/defnull/bottle
Reading http://bottlepy.org/
Best match: bottle 0.11.4
Downloading http://pypi.python.org/packages/source/b/bottle/bottle-0.11.4.tar.gz#md5=f767c340de0b7c9581917c48e609479b
Processing bottle-0.11.4.tar.gz
Running bottle-0.11.4\setup.py -q bdist_egg –dist-dir c:\users\woo\appdata\local\temp\easy_install-5b4qq6\bottle-0.11.4\egg-dist-tmp-q2yd68
zip_safe flag not set; analyzing archive contents…
bottle: module references __file__
bottle: module references __path__
Adding bottle 0.11.4 to easy-install.pth file
Installing bottle.py script to C:\OSGeo4W\apps\Python27\Scripts
Installed c:\osgeo4w\apps\python27\lib\site-packages\bottle-0.11.4-py2.7.egg
Processing dependencies for bottle
Finished processing dependencies for bottle

Install pip

• You should also install pip as it is a better package manager then easy_install
• Just run easy_install pip

Note

Most of the time any Python packages that are needed by your OSGeo4W tools are bundled in the installer and can be downloaded using the OSGeo4W installer, however there have been cases when I wanted to install a non OSGeo4W package into my setup by using easy_install or pip. Like bottle and flask in the example above.

Filed under: Open Source Tagged: FOSSGIS, osgeo, python, qgis, Quantum GIS

The OSGeo Board of Directors have named Jeff McKenna as its new President. The previous President, Frank Warmerdam, has stepped down, and the OSGeo Board is extremely grateful for his leadership. Mr. McKenna brings years of experience in the geospatial industry, and has been involved in the MapServer web mapping project since its early days. He was also one of the founding forces behind the Free and Open Source Software for Geospatial (FOSS4G) international conference, and has dedicated himself to promoting the use of Open Source geospatial software through FOSS4G events all around the world.

Mr. McKenna explains, “I'm honored to be named as the new President of OSGeo. I plan to continue the wonderful work of our past presidents Frank and Arnulf. The OSGeo community is now thriving and vibrant, with FOSS4G regional events operating all across the world; I plan to continue spreading this passion for Open Source geospatial, and help introduce our knowledge to both decision makers and technical users.  Decision makers all around the world should be exposed to our experts through our communities, our regional events, our local chapters, and also through our professional service providers.  There is much work still to be done in spreading our knowledge of Open Source geospatial through all of these networks.”

The GRASS GIS team will organize a GRASS GIS Community Sprint from 2-7 Feb, 2013 in Genova, Italy. The sprint is at the same time of the "XIV Meeting degli Utenti Italiani GRASS e Gfoss" at the University of Genova.

We would like to invite you to financially support this upcoming Community Sprint! The past sprints have been very successful as we expect for the upcoming one.

Important Web page:
http://grass.osgeo.org/wiki/GRASS_Community_Sprint_Genova_2013

Please consider to donate:
http://grass.osgeo.org/donations/

Background info
The GRASS GIS Community Sprint is a great occasion for folks to support the development by actively contributing to the source code, manuals or likewise. The community sprint is a get-together for GRASS project members and supporters and related OSGeo projects to take decisions and tackle larger problems. For this meeting, we welcome people committed to improving the GRASS GIS project and the interfaces to QGIS, GDAL, PostGIS, R-stats. Sextante. gvSIG, OGC Services and more. This includes developers, documenters, bug reporters, translators and other OSGeo supporters. Not only the "C Tribe" will be addressed but also Python or whatever the participants prefer.

As QGIS is such a fast moving project I have decided to make this a regular blog post in order to highlight some new features added to QGIS. If you haven’t already, don’t forget to check out round one.

Remember that some of these features may still only be new which might change between now and the next official released version. With that out of the way lets get listing.

Atlas integration

If you are a regular user of QGIS Python plugins, and who isn’t, then you would have used the awesome Atlas plugin developed by Vincent Picavet. This great tool can be used to generate mapbooks, or an atlas as some people like to say, using a coverage layer and a print composer. What makes this even more awesome is that it is now built into the print composer.

The builtin atlas function also gives you the ability to use an expression to do runtime text replacement, including access to all the fields on the coverage layer.  The coverage layer doesn’t even have to be a region layer, it can be a simple point layer, or even a line layer.   You can see the result of me running the atlas generation from the above example here

Big thanks to Oslandia for integrating this great feature, and the companies sponsoring the work.

New Python console

This new addition comes from the great work that Salvatore Larosa has been doing to add a better Python console to QGIS.

The new Python console includes attribute auto complete, syntax highlighting, better copy and paste, uploading to codepad, the ability to run code from a file, etc.  You don’t realise how much difference there is until you go back to using the old one in version 1.8.

Tabbed and groups in builtin forms

One of the things I really loved about QGIS, coming from MapInfo, was the builtin forms.  Just having the ability to enter data using controls like combo boxes, calendar widgets, etc makes you one step closer to having better data.   This feature is the exact reason I setup a 67 year old for kerb data collection.

As good as they are the builtin forms have an issue of ending up with as a big scrolling list with lots of fields; also the lack of  the ability to group or put fields on tabs in the UI meant you had to create a custom form.  Well not any more.

There is now a combo box on the Fields tab that allows you to build a generated form but also add tabs and group boxes.  You can even have the same field shown more then once on the form, handy for something like an ID field that you would like to show on each tab.

With this new ability the builtin forms can get me 95% of the way for data entry jobs, the other 5% I just make a custom form – but that is very rare.

Sextante

Sextante is a great and powerful analytical framework that has been added to the core of QGIS thanks to Victor Olaya.  This is not a feature that I use a lot but this is only due to most of my work being in development and not analysis, however that doesn’t mean that it’s not a really cool feature.

One of the greatest things about the Sextante toolbox is that it allows you to integrate other great open source tools like GRASS, SAGA, R, OTB, etc, right into your QGIS workflow and view the results in the canvas. It even includes a modeller so that you can build a connected diagram of all the bits of your process, even if it crosses between programs.

For me what is even better is that you can use Sextante in your plugins or custom Python code.  Sextante has a Python interface – well the whole thing is written in Python – that you can use to run a Sextante supported algorithm.

import sextante
outputs_0=sextante.runalg("grass:v.crossbones", /file, 0, ,, 1, 2, 3, 4, 1=3.0,2=8.0,5=6.0,8=6.0,11=6.0,14=6.0, None)
outputs_1=sextante.runalg("grass:v.delaunay", outputs_0['output'], True, True, None)
outputs_2=sextante.runalg("grass:v.dissolve", outputs_0['output'], , None)

Victor has created a blog to cover some Sextante recipes at QGIS-SEXTANTE cookbook/. There are also some really cool example of Sextante in use at:

• http://www.qgis.org/en/community/qgis-case-studies/pinhel-portugal.html
• http://www.qgis.org/en/community/qgis-case-studies/lisbon-portugal.html

Massive amount of composer additions

This last feature, or rather feature set,  comes from the sponsorship and support of the World Bank, Australia-Indonesia Facility for Disaster Reduction, Geoscience Australia and the GFDRR.  Most of this work was done to aid in the development of a new QGIS plugin called inaSAFE, which has also received some great praise

“(InaSAFE) is very beneficial for all of us. It’s a good example of our partnership.”
Dr Susilo Bambang Yudhoyono – President of Indonesia

Some of the improvements include:

• A new loadFromTemplate method, in the API, that can do text replacement in the QGIS composer template.
• Better support for EPSG:4326 scale bars
• Multipage in one composer
• Automatic overview frame in map frame
• HTML frame
• Zebra style grid frame border
• More control of grid labels. Inside, outside, disabled
• etc, etc

These are great additions to the QGIS composer and I have already used the overview frame feature along with the new atlas integration  to make some quick nice looking map books. \

A huge thanks to the World Bank, Australia-Indonesia Facility for Disaster Reduction, Geoscience Australia and the GFDRR, and all the developers included.

You can see some of the output that InaSAFE generates using some of these new features at http://quake.linfiniti.com/

P.S The World Bank also sponsored the new raster Save As.. ability just like we have for vector layers.

 

Filed under: Open Source, qgis Tagged: FOSSGIS, gis, Open Source, osgeo, qgis, Quantum GIS

Last Thursday and Friday was our first local Australian FOSS4G event which was hosted at the CSRIO building in Brisbane.  Very big thanks to CSRIO for hosting the event.  The venue was setup perfectly for  hosting an event like this, including dual projectors for presenting, video calls over to Perth, etc.

The first day was done using a un-conference style of event. This is the first time I’ve been to a un-conference and I liked the format a lot.   Once everyone was there on the first morning we collected ideas from people and everyone voted on which ones they would like to see.  After we had picked enough topics Shaun and I made a program for the day and we started.

Topics included:

• State of GeoServer
• QMap
• CouchDB
• Moblie mapping
• Full open source stacks
• Open Source GIS in Education

The second day was a code sprint.  I worked on converting a MapBasic scripts from one of the guys to QGIS, and Jody enlisted the others to help check the headers of the GeoServer project so that it can finally pass OSGeo incubation.

Overall I think it was a very successful event.  I would like to make these a yearly event if we can, provided that we have people to talk, or projects to work on.

More information about up coming OSGeo events in Australia and New Zealand can be found at http://www.meetup.com/osgeo-aust-nz/

Filed under: Open Source, qgis Tagged: FOSSGIS, gis, Open Source, open source gis, osgeo, qgis, Quantum GIS

Earlier this Last year, in June, Don Meltz wrote an interesting blog "ArcGIS vs QGIS Clipping Contest Rematch" where he let compete ArcGIS and Quantum GIS in a clipping contest. The benchmark contest data set in question is a 878MB ZIP file (ContourClipTest.zip). The blog page gained a lot of comments, even from ESRI since some ArcGIS versions crashed on this test data set.

Find below the various timings compiled from the blog and the comments:

Proprietary software

Software	Processing time	Hardware/Software
ArcGIS 9.3	crash after 1h 9min: ERROR 999999: Error executing function. Invalid Topology [4gb file limit.] Failed to execute (Clip)	unknown
ArcGIS 10.0	crash likewise	unknown
ArcGIS 10.1	ESRI promise to calculate it in 34 seconds in this updated version (did anyone test?)	unknown
GlobalMapper (version?)	30 mins	unknown
GlobalMapper v11.02	49 sec	Windows XP w/ 3.5GB RAM
Manifold 8 (64bit)	31 min	Windows XP64 16 gb. RAM and 2.33 GHz

Note: The two GlobalMapper results are a bit funny, perhaps always minutes?

Free and Open Source Software

Software	Processing time	Hardware/Software
Quantum GIS (version?; Simple features)	4-5 min	unknown
GRASS GIS 7 (topological GIS)	5 min	Dell PowerEdge 2950 from 2008, Intel Xeon 2.66GHz, 8GB RAM
gvSIG	to be done
PostGIS	to be done

Notes: Hope volunteers will test this also on gvSIG and PostGIS (and other FOSSGIS)! Please report...

The program of the GFOSSDAY 2012 + OSMit2012 @ Torino, Italy, has been published:
http://www.gfoss.it/drupal/gfossday2012/programma

We offer there a GRASS GIS workshop on Friday 16th Nov 2012 at 9:30. You are welcome!

Location:
Centro Incontri Regione Piemonte, Corso Stati Uniti 23, Torino, Italy

Another quick announcement for today. The local FOSS4G-AU chapter is holding un-conference and code sprint in Brisbane on the 15 and 16th of November 2012.

Ben Caradoc-Davies made the announcement on the mailing list the other day:

The Free and Open Source Software for Geospatial Australia (FOSS4G-AU)
2012 Unconference and Code Sprint will be held at CSIRO’s Queensland
Centre for Advanced Technologies (QCAT), Pullenvale QLD.
15 November: Unconference
16 November: Code Sprint
This is a participant-organised event: please add your unconference and code sprint topic suggestions to the wiki. Organisers are welcome; please speak up.

See here for details: http://wiki.osgeo.org/wiki/FOSS4G-AU_2012

RSVP essential for building access. Please sign up here:
http://www.meetup.com/osgeo-aust-nz/events/83965312/

Email: aust-nz@lists.osgeo.org (sign up here http://lists.osgeo.org/mailman/listinfo/aust-na)

Kind regards,
Ben Caradoc-Davies
Software Engineer
CSIRO Earth Science and Resource Engineering
Australian Resources Research Centre

Being part of osgeo-aust-nz and the local Australian open source GIS movement it’s great to see events like this being organized.

I’ll be there, most likely pimping some QGIS stuff.

Hope to see you there.

Just remember that RSVP is essential to get into the building.

Filed under: Open Source Tagged: foss4g, FOSSGIS, osgeo, qgis

Just a quick post to let everyone know that DMS will be running QGIS training on the 20 Nov 2012 to the 21 Nov 2012 in Brisbane, QLD. More information can be found at http://mapsolutions.com.au/training/quantum-gis/introduction-to-qgis.aspx

Other dates include:

23 Oct 2012 – 24 Oct 2012 – Perth
13 Nov 2012 – 14 Nov 2012 – Perth
20 Nov 2012 – 21 Nov 2012 – Brisbane
22 Nov 2012 – 23 Nov 2012 – Melbourne

Filed under: Open Source, qgis Tagged: osgeo, qgis, Quantum GIS

In winGRASS 7 (download standalone installer) the Windows batchfiles for use with R (http://code.google.com/p/batchfiles/) are now integrated for a smooth GRASS-R-coupling in MS-Windows. For the usage see here:
http://grass.osgeo.org/wiki/R_statistics#Usage_III

Note that this integration is available for Linux users for a long time, however, finally also the winGRASS user can enjoy this integration!

Thanks to Helmut Kudrnovsky from the GRASS GIS team and to the Windows batchfiles for use with R team.

I’m very please to announce the Australian QGIS User Group. Chris Scott (DMS) and I created this group because the interest in QGIS here is growing fast and it would be nice to have a place where us Aussies can hang out and chat about QGIS stuff, discuss local issues, organize local events, put shrimps on the barbie.

My ultimate goal would be to turn this into a full user group much like the Swiss QGIS User Group but for now we will keep it light.

Everyone is free to view the content of the home page and the Google group, however you have to request to join the Google Group to post.  This is only so that we can keep it local and not reduce the official QGIS mailing lists.

So in saying all that. If you live in Australia. Use QGIS, or are interested in QGIS. Feel free to join the group.

Filed under: Open Source, qgis Tagged: FOSSGIS, gis, Open Source, osgeo, qgis, Quantum GIS

Something that I need to do now and then is generate points along a line at supplied distance.  I had never really looked into doing it in QGIS until this question poped up on gis.stackexchange.com.  This is a quick blog post because I thought it was a pretty handy little thing to do.

In the development version there is a new method on QgsGeometry called interpolate. This method takes a distance and returns a point along a line at that distance. Perfect! We can then just wrap this in a loop and generate a point increasing the distance as we move along

from qgis.core import (QgsFeature, QgsGeometry,
                       QgsVectorLayer, QgsMapLayerRegistry,
                       QgsField)
from PyQt4.QtCore import QVariant
from qgis.utils import iface

def createPointsAt(distance, geom):
    length = geom.length()
    currentdistance = distance
    feats = []

    while currentdistance < length:
        # Get a point along the line at the current distance
        point = geom.interpolate(currentdistance)
        # Create a new QgsFeature and assign it the new geometry
        fet = QgsFeature()
        fet.setAttributeMap( { 0 : currentdistance } )
        fet.setGeometry(point)
        feats.append(fet)
        # Increase the distance
        currentdistance = currentdistance + distance

    return feats

def pointsAlongLine(distance):
    # Create a new memory layer and add a distance attribute
    vl = QgsVectorLayer("Point", "distance nodes", "memory")
    pr = vl.dataProvider()
    pr.addAttributes( [ QgsField("distance", QVariant.Int) ] )
    layer = iface.mapCanvas().currentLayer()
    # Loop though all the selected features
    for feature in layer.selectedFeatures():
        geom = feature.geometry()
        features = createPointsAt(distance, geom)
        pr.addFeatures(features)
        vl.updateExtents()

    QgsMapLayerRegistry.instance().addMapLayer(vl)

The above code might look a bit scary at first if you have never done any Python/pyqgis but hopefully the comments will ease the pain a little. The main bit is the createPointsAt function.

Cool! If we want to use this we can just stick it in a file in the .qgis/python folder (lets call it pointtools.py) and then run import pointtools in the python console.

So lets have a go. First select some objects then run the following in the Python Console

import pointtools
pointtools.pointsAlongLine(40)

That will generate a point every 40 meters along then selected lines

To generate nodes along different lines, select the new features, then call pointtools.pointsAlongLine(40) in the Python console.

Simple as that!

(Who knows, someone (maybe me) might even add this as a core object function in QGIS in the future)

Filed under: Open Source, qgis Tagged: language python, Open Source, osgeo, pyqgis, python, qgis, qgis-tips, Quantum GIS, tips

Atlas is a super handy little QGIS plugin that lets you generate a map series from a composer and a coverage (grid) layer.

The authors of the plugin are now looking for some funding to make it a core part of QGIS.  Making it part of QGIS would mean integration into the composer and maybe APIs for developers to add extensions.

The authors are looking at raising 7000€ in order top get the work done, but the more money raised the more features that are added.

More information can be found at http://www.oslandia.com/?p=1243

Filed under: Open Source, qgis Tagged: FOSSGIS, Open Source, osgeo, qgis, Quantum GIS

Version note: This will only work in the latest dev build of QGIS – not in 1.8

The lack of uni for the next couple of weeks has left me some time at night to work on some features that I really wish QGIS had.  One of these features was better date and time support in the expression engine.  Date and time is an important concept when working on inspection data and not being able to style my features in QGIS using date operations was bugging me.  So in good open source fashion I added some.

Here are the current functions (more to come in the future):

• $now – returns the current date and time
• age({datetime},{datetime}) - returns the difference between the two dates
• todate({string}) - converts a string to date type
• totime({string}) – converts a string to time type
• tointerval({string}) – converts a string to a interval type (details below)
• day({datetime} or {interval}) – returns the day from a datetime type or the number of days in a interval.
• hour(…) – Same as above but for hours
• minute(…)  - Same as above but for minutes
• second(…)  - Same as above but for seconds
• day(..)  - Same as above but for days
• week(..)  - Same as above but for weeks
• month(…)  - Same as above but for months
• year(…) - Same as above but for years
• {datetime} – {interval} = {new datetime} – returns a new datetime subtracting the interval 
• {datetime} + {interval} = {new datetime} – returns a new datetime adding the interval

The interval type

Functions like age(..), tointerval(), {datetime} -/+ {interval}, day(..), hour(..), etc, use, or return, Intervals.  An Interval is a measure of time that we can use for different things.  An example of an Interval is ’1 Year 2 Months’ this is then converted to a number of seconds and used for any calculations.

For example one can take away 10 days from the current date by doing the following ( -> marks the output ):

todate($now - '10 Days')
-> 2012-06-20

as

todate($now)
-> 2012-06-30

We can also do something like:

todate($now + '2 Years 1 Month 10 Days')
-> 2014-08-10

The age() function will return an interval which we can use extract what information we need.

The number of days between two dates:

day(age('2012-06-30', '2012-06-10'))
-> 20
-- Think of it as '2012-06-30' - '2012-06-10'
-- Note: day(), month(), etc, functions return doubles so you can get
-- 21.135234 days if you are using date & time type rather than just date type
-- wrap the result in toint() to get a more sane output.

Day() will also work on a plain date:

day('2012-06-30')
-> 30

We can even get the number of seconds between two dates:

second(age('2012-06-30', '2012-06-10'))
-> 1728000

Currently the only date format supported is {year}-{month}-{day} as seen in the examples above. Shouldn’t be too hard to add support to the todate(), todatetime(), totime() functions for giving it a pattern to use when converting the string e.g. dd-mm-YYYY, or something like that.

More on this fancy new stuff

When I wrote the new expression builder dialog a while ago I made it dynamic so that any new functions added to the expression engine will show up automatically.  So here they are:

We can also use these functions in the rule based rending, which is where the power really comes in.  Lets see something like that in action:

Should be pretty straight forward to understand. We are using the age() and day() functions to style the events that are older than 30 days, within 30 days, for today, or in the future.  We also check the year of the event using year() and year($now) to make sure we only see this years events, or style them differently depending on if they are last years events or in the future.

This is the result of the above rules:

I’m also using the date functions in the expression based labelling to label the features using the following expression:

CASE
WHEN year( "dateadded") < year($now) THEN
	'Last Year'
WHEN day(age("dateadded", $now)) < 0 THEN
	day(age("dateadded", todate($now))) || ' Days old'
ELSE
	day(age("dateadded", todate($now))) || ' Days to go'
END

Well that’s it. Hope you find it handy in your day-to-day mapping. I know I will be using it a lot.
Thanks to Martin and Jürgen for the code reviews during the process; venturing in an unknown part of the code base always makes me nervous but that is all part of learning, and sometimes you can make some pretty cool stuff.
Some other random notes: The general idea has been modelled of how Postgres handles dates and times, it’s not an exact copy but follows the same kind of ideas. The interval class also uses the same number of seconds for one year that postgres does so that we can be consistent with the output.

Filed under: Open Source, qgis Tagged: FOSSGIS, gis, map-rendering, Open Source, osgeo, qgis, Quantum GIS, styling

So this years first uni semester is done and dusted, now I have some free time.  Blog all the things!

This is a follow up post for discussion that was started on LinkedIn about showing features older, or newer, then a certain date different colours   The main post was about using free, or low cost, solutions in order to aid in mapping water networks. I recommend that everyone watch it. A very good presentation.

I recommended that you could use the rule based rendering engine but the expression engine in QGIS doesn’t have any date functions yet.  All good we can add them if we need and once I get my head around the expression engine I plan on doing exactly that. But for now we can do it a different way.

We are going to use Spatialite, but any database will do (syntax and process will vary).

Lets have a look an inspection layer we have in our Spatialite database viewed in QGIS:

Pretty boring and hard to see what has been done in the last 30 days.  Now with the lack of support for dates in the expression engine we have to use another methods.  For this example we will use the really handy DBManger plugin that now ships with QGIS from 1.8.  Load it, connect to your database, and run the following query:

SELECT id,
              CASE WHEN DATE("date_checked") > DATE('now', '-30 days') THEN
                         'Within 30 Days'
              ELSE
                         'older'
              END as age, date_checked, geom
FROM  "inspections"

As you can see anything that is within the 30 days now has the “Within 30 Days” string in the age column, or else it has “older”.  CASE statements can be very powerful things in SQL sometimes.

Now load it into QGIS, style, and label it using the new age column

and Bob’s your uncle

You now have a layer that is style based on age but is also dynamic.  Adding a new inspection point will now will be styled according to those rules. (Although you will have to edit the normal inspection layer with it turned off as views/queries are not editable – without some setup anyway)

It might be a simple thing to some but sometimes it’s hard to find the right words to describe what you want when you are looking for this kind of thing. So hopefully this has helped a few people get started with visualizing their time/date based data in QGIS.

Happy mapping!

Filed under: Open Source, qgis Tagged: FOSSGIS, gis, Open Source, osgeo, qgis, Quantum GIS, styling