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Mon May 2 21:55:13 2016

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How to create round maps in Print Composer

If you follow me on Twitter, you’ve probably seen previews of my experiments with round maps. These experiments were motivated by a recent question on GIS.stackexchange whether this type of map can be created in QGIS and while it’s not very convenient right now, it is definitely possible:

http://www.quantarctica.org

All maps in this post are created using data from the Quantarctica project.

I’ve been planing to try the Quantarctica datasets for a long time and this use case is just perfect. When you download and open their project, you’ll see that they have already clipped all datasets to a circle around Antarctica:

Quantarctica project with some custom styling

Quantarctica project with some custom styling

Since the map of the full extent of the dataset is already clipped to a circle, the overview map is easy to deal with. The detail map on the other hand is rectangular by default:

circle_maps_start

Since we cannot change the shape of the map item, we have to use a mask instead. To create a circular mask, we can add an ellipse shape:

circle_maps_addellipse

The main challenge when creating the mask is that there is no inverted polygon renderer for shapes in print composer. I’ve evaluated to workarounds: First, I created a style with a wide white outline that would cover all map parts outside the circle shape. But this solution slowed the print composer down a lot. An alternative, which doesn’t suffer from this slowdown is using draw effects:

circle_maps_mask_style

In particular, I created a big outer glow effect:

circle_maps_mask_style_effect

Note that the effect only works if the symbol itself is not transparent. That’s why I set the symbol fill to black and used the Lighten blending mode:

circle_maps_mask

Voilà! Both maps appear are nicely circular.

It is worth noting though that this workaround has a downside: it is not possible to create automatic grids/graticules for these maps. The graticule in the overview map only works because it is a layer in the main project that was already clipped to the circular shape.

Finally, you can add more depth to your map by adding shadows. To create the shadow effect, I added additional ellipse items which are styled with a drop shadow draw effect. If you only enable the drop shadow effect, you will notice that the shadow is cut off at the ellipse bounding box. To avoid this undesired effect, you can add a transform effect, which reduces the size of the drawn shape and it’s shadow so that the shadow fits into the bounding box:

circle_maps_mask_shadow_effect

It requires some manual adjustments to place the shadow at the optimal location on top of the mask:

circle_maps_mask_shadow

Add another ellipse to create the shadow for the overview map.

For more cartography tips and tricks check my new book QGIS Map Design or join my QGIS training courses.


Interview: QGIS in journalism

Last year, I published the short post QGIS on the rise with journalists showcasing how QGIS is used by journalists with examples from the Los Angeles Times and Financial Times.

The latest QGIS case study now features an interview with Steven Bernard (Interactive Design Editor at the Financial Times) by A. Neumann and T. Sutton.

QGIS is now an integral part of our mapping workflow. (…) I would say 80% of our maps are now produced in QGIS. read more …

It’s great to see all the great examples of QGIS used to communicate international news. Thanks to everyone involved in this interview for sharing this case study with the community!


Learning QGIS 3rd ed. discounts

In time for QGIS 2.14 (soon to be LTR), I have updated “Learning QGIS” to reflect the latest improvements of our favorite GIS.

To celebrate, we are giving away 100 copies of the book at 30% (for print) and 50% (for eBook) discount if you use the following codes:

30% off  the Print version
Code: prt30LeaQS

50% off the eBook version
Code: LeaQSebok50

(Codes are valid until 30th April 2016 or we’ve reached 100 copies.)

B05278_MockupCover_Normal


New demos: live labels & gradient editor

Following up on last week’s post, Nyall has continued his work on the QGIS gradient editor:

Latest version of the new QGIS interactive gradient edit. This now includes an interactive plot of the color hue/saturation/lightness/alpha, allowing a visual overview of these color components and easy editing.

Another equally awesome demo has been posted by Nathan, who is currently working on usability improvements for labeling and styling without blocking dialogs:

This is going to be great for map design work because it makes many complex styles much easier to create since you can interact with the map and attribute table at the same time.

These are definitely two developments to follow closely!


Towards better gradients

Interesting developments going on if you like creating your own gradients. After all, that’s not as easy as it might initially seem, as Gregor Aisch describes in his post “Mastering Multi-hued Color Scales with Chroma.js”:

The issues with simple color interpolations, which include nonuniform changes in lightness between classes, also haunt us in cartography. Just have a look at the map and legend on the left-hand side, which has been created using a normal custom QGIS gradient with colors ranging from black to red, yellow and finally white. We end up with three classes in yellow which are nearly impossible to tell apart:

comparing_ramps

For comparison, on the right side, I’ve used Gregor’s corrected color ramp, which ensures that lightness changes evenly from one class to the next.

Wouldn’t it be great if the built-in gradient tool in QGIS could correct for lightness? Too bad the current dialog is not that great:

My first reaction therefore was to write a short script to import gradients from Gregor’s Chroma.js Color Scale Helper into QGIS:

But we’ll probably have a much better solution in QGIS soon since Nyall Dawson has picked up the idea and is already working on a completely new version of the gradient tool. You can see a demo of the current work in progress here:

I’m really looking forward to trying this out once it hits master!


How to fix the Windows config for .qgs default program

This is a short tip for you if you use QGIS on Windows and ended up with an error like this:

The program can't start because qgis_app.dll is missing from your computer. Try reinstalling the program to fix the problem.

Windows’ suggestion to reinstall probably won’t fix this issue. Instead, you want Windows to run qgis.bat instead of any .exe it is trying to use. Right-click a .qgs file and go to Open with | Choose default program:

Screenshot 2016-03-26 16.22.15

In OSGeo4W, the .bat file is located in the bin folder:

Screenshot 2016-03-26 16.27.01

Happy QGISing!


Creating dynamic icon series

Today’s post was motivated by a question on GIS.StackExchange, which is looking for an automated way to symbolize the amenities available at a location using a series of icons, like this:

Screenshot 2016-03-19 23.02.30

Assuming the information is available in  a format similar to this example attribute table

Screenshot 2016-03-19 23.02.00

we can create a symbol, which adapts to the values in the icon columns using data-defined overrides:

Screenshot 2016-03-19 23.04.17

The five potential symbol locations are aligned next to each other using offsets. We use the following expression to determine the correct SVG symbol:

CASE
WHEN "icon4" = 'dinner'
 THEN 'C:/OSGeo4W64/apps/qgis-dev/svg/entertainment/amenity=restaurant.svg'
WHEN "icon4" = 'sleep'
 THEN 'C:/OSGeo4W64/apps/qgis-dev/svg/accommodation/accommodation_hotel2.svg'
WHEN "icon4" = 'ship'
 THEN 'C:/OSGeo4W64/apps/qgis-dev/svg/transport/amenity=ferry_terminal.svg'
WHEN "icon4" = 'house'
 THEN 'C:/OSGeo4W64/apps/qgis-dev/svg/accommodation/accommodation_house.svg'
 ELSE  ''
END

To hide icons if the icon value is NULL, the marker size is set to 0 using, for example:

CASE
WHEN "icon4" is not NULL
 THEN 4
 ELSE 0
END

Finally, to ensure that the labels don’t cover the icons, we can use the cartographic label placement with the position priority set to ‘TR,TL,BL’, which restricts labels to the top right, top left, and bottom left position.

Screenshot 2016-03-19 23.04.43

With these settings in place, we can zoom out and the labeling algorithm picks the most suitable position from the list of allowed positions:

Screenshot 2016-03-19 23.02.11

For more cartography tips and tricks check my new book QGIS Map Design or join my QGIS training courses.


How to create a graduated renderer for polygon borders instead of fills

Today’s post was motivated by a recent question on the #gistribe Twitter chat:

So what’s the issue?

Default polygon symbols come with a fill and a border color:

Screenshot 2016-03-12 15.40.37

When they are used in a graduated renderer, the fill color is altered for each class:

Screenshot 2016-03-12 15.40.26

What if you want to change the border color instead?

The simplest solution is to add an outline symbol layer to your polygon symbol:

Screenshot 2016-03-12 15.40.46

The outline layer has only one color property and it will be altered by the graduated renderer.

If you now hit ok, the graduated renderer will alter both the simple fill’s fill color and the outline’s color. To stop the fill color from changing, select the simple fill and lock it using the small lock icon below the list of symbol layers:

Screenshot 2016-03-12 15.40.50

Voilà:

Screenshot 2016-03-12 15.40.58

For more cartography tips and tricks check my new book QGIS Map Design or join my QGIS training courses.


Better digitizing with QGIS 2.14

Tracing button

If you are using QGIS for digitizing work, you have probably seen the 2.14 Changelog entry for Trace Digitizing. The main reason why this is a really cool new feature is that it speeds up digitizing a lot. When tracing is enabled, the digitizing tools take care to follow existing features (as configured in the snapping options). For a detailed howto and videos check Lutra’s blog.


QGIS Map Design is out now!

My latest book “QGIS Map Design”, co-authored with well-known cartography expert Gretchen Peterson and with a foreword by the founder of QGIS, Gary Sherman himself, is now available as e-book.

In three parts, the book covers layer styling, labeling, and designing print maps. All recipes come with data and project files so you can reproduce the maps yourself.

Check the book website for the table of contents and a sample chapter.

Just in time for the big QGIS 2.14 LTR release, the paperback will be available March 1st.

On a related note, I am also currently reviewing the latest proofs of the 3rd edition of “Learning QGIS”, which will be updated to QGIS 2.14 as well.

Happy QGISing!


Experiments in the 3rd dimension

The upcoming 2.14 release of QGIS features a new renderer. For the first time in QGIS history, it will be possible to render 2.5D objects directly in the map window. This feature is the result of a successful crowd funding campaign organized by Matthias Kuhn last year.

In this post, I’ll showcase this new renderer and compare the achievable results to output from the Qgis2threejs plugin.

For this post, I’m using building parts data from the city of Vienna, which is publicly available through their data viewer:

This dataset is a pretty detailed building model, where each building is made up of multiple features that represent parts of the building with different height. Of course, if we just load the dataset in default style, we cannot really appreciate the data:

Loaded building parts layer

Loaded building parts layer

All this changes if we use the new 2.5D renderer. With just a few basic settings, we can create 2.5D representations of the building parts:

QGIS 2.5D renderer settings

QGIS 2.5D renderer settings

Compare the results to aerial images in Google Maps …

QGIS 2.5D renderer and view in Google Maps

QGIS 2.5D renderer and view in Google Maps

… not bad at all!

Except for a few glitches concerning the small towers at the corners of the building, and some situations where it seems like the wrong building part is drawn in the front, the 2.5D look is quite impressive.

Now, how does this compare to Qgis2threejs, one of the popular plugins which uses web technologies to render 3D content?

One obvious disadvantage of Qgis2threejs is that we cannot define a dedicated roof color. Thus the whole block is drawn in the same color.

On the other hand, Qgis2threejs does not suffer from the rendering order issues that we observe in the QGIS 2.5D renderer and the small towers in the building corners are correctly displayed as well:

QGIS 2.5D renderer and QGIS2threejs output

QGIS 2.5D renderer and Qgis2threejs output

Overall, the 2.5D renderer is a really fun and exciting new feature. Besides the obvious building usecase, I’m sure we will see a lot of thematic maps making use of this as well.

Give it a try!

In the next post, I’m planning a more in-depth look into how the 2.5D renderer works. Here’s a small teaser of what’s possible if you are not afraid to get your hands dirty:


QGIS 3.0 plans

News about the path to QGIS 3.0 …

QGIS.org blog

qgis-icon-60x60

Ok so quick spoiler here: there is no QGIS 3.0 ready yet, nor will there be a QGIS 3.0 for some time. This article provides a bit more detail on the plans for QGIS 3.0. A few weeks ago I wrote about some of the considerations for the 3.0 release, so you may want to read that first before continuing with this article as I do not cover the same ground here.

lot of consideration has gone into deciding what the approach will be for the development of QGIS 3.0. Unfortunately the first PSC vote regarding which proposal to follow was a split decision (4 for, 3 against, 1 abstention and 1 suggestion for an alternative in the discussion). During our PSC meeting this week we re-tabled the topic and eventually agreed on Jürgen Fischer’s proposal (Jürgen is a QGIS PSC Member and the QGIS Release Manager) by a much more unanimous…

View original post 1,208 more words


A QGIS router for GIP.at

Monday, January 4th 2016, was the open data release date of the official Austrian street network dataset called GIP.at. As far as I know, the dataset is not totally complete yet but it should be in the upcoming months. I’ve blogged about GIP.at before in Open source IDF parser for QGIS and Open source IDF router for QGIS where I was implementing tools based on the data samples that were available then. Naturally, I was very curious if my parser and particularly the router could handle the whole country release …

Some code tweaking, patience for loading, and 9GB of RAM later, QGIS happily routes through Austria, for example from my work place to Salzburg – maybe for some skiing:

Screenshot 2016-01-06 17.11.27

The routing request itself takes something between 1 and 2 seconds. (I should still add a timer to it.)

So far, I’ve implemented shortest distance routing for pedestrians, bikes, and cars. Since the data also contains travel speeds, it should be quite straight-forward to also add shortest travel time routing.

The code is available on Github for you to try. I’d appreciate any feedback!


Talking QGIS with UNIGIS Salzburg

Last summer, I had the pleasure to talk with UNIGIS Salzburg about the QGIS project: how it works and what makes it great. Now, finally, the video is out on Youtube:

Amongst other things, we are discussing the UNIGIS module on QGIS, which I have been teaching for the past few months.


How to label only selected features in QGIS 2.8 and up

In 2011, I wrote “How to Label Only Selected Features in QGIS” which ends with the wish that

Another “data defined setting” like “show this label (true/false)” would be more intuitive.

… and now we have it!

It’s called Show label and you can find it in the Rendering section of the labeling dialog.

The following screenshot shows a quick example of how to label only airports starting with A by setting the expression

"NAME" LIKE 'A%'

labelselected

This post was motivated by a question by Eduardo here on this blog. Hope it helps!


How to create connectivity-based line caps

It’s been a while since my last blog post mostly because I’ve been busy with some more long form writing. Most notably, I’ve been writing a paper on the QGIS Projcessing framework in the open access ISPRS International Journal of Geo-Information together with Victor Olaya and I’m still in the process of writing a new book titled “QGIS Map Design” together with Gretchen Peterson which is scheduled for early 2016.

Today’s post has been on my todo list for a while now. It’s inspired by a talk at a recent cartography conference I attended:

(For a summary of the whole event, check the storify I compiled.)

The idea of this slide and several more was to show all the attention to detail which goes into designing a good road map. One aspect seemed particularly interesting to me since I had never considered it before: what do we communicate by our choice of line caps? The speaker argued that we need different caps for different situations, such as closed square caps at the end of a road and open flat caps when a road turns into a narrower path.

I’ve been playing with this idea to see how to reproduce the effect in QGIS …

So first of all, I created a small test dataset with different types of road classes. The dataset is pretty simple but the key to recreating the style is in the attributes for the road’s end node degree values (degree_fro and degree_to), the link’s road class as well as the class of the adjacent roads (class_to and class_from). The degree value simply states how many lines connect to a certain network node. So a dead end as a degree of 1, a t-shaped intersection has a degree of 3, and so on. The adjacent class columns are only filled if the a neighbor is of class minor since I don’t have a use for any other values in this example. Filling the degree and adjacent class columns is something that certainly could be automated but I haven’t looked into that yet.

roadattributes

 

The layer is then styled using rules. There is one rule for each road class value. Rendering order is used to ensure that bridges are drawn on top of all other lines.

roadrules

Now for the juicy part: the caps are defined using a data-defined expression. The goal of the expression is to detect where a road turns into a narrow path and use a flat cap there. In all other cases, square cap should be used.

roadrule

Like some of you noted on Twitter after I posted the first preview, there is one issue and that is that we can only set one cap style per line and it will affect both ends of the line in the same way. In practice though, I’m not sure this will actually cause any issues in the majority of cases.

I wonder if it would be possible to automate this style in a way such that it doesn’t require any precomputed attributes but instead uses some custom functions in the data-defined expressions which determine the correct style on the fly. Let me know if you try it!


Take part in the QGIS user survey

The QGIS project is asking for user feedback to gain a better understanding of the wishes and requirements of its user base. Please take part in the survey and share the links with other QGIS users. The survey is available in multiple languages:


Quick webmaps with qgis2web

In Publishing interactive web maps using QGIS, I presented two plugins for exporting web maps from QGIS. Today, I want to add an new member to this family: the qgis2web plugin is the successor of qgis-ol3 and combines exports to both OpenLayers3 as well as Leaflet.

The plugin is under active development and currently not all features are supported for both OpenLayers3 and Leaflet, but it’s a very convenient way to kick-off a quick webmapping project.

Here’s an example of an OpenLayers3 preview with enabled popups:

OpenLayers3 preview

OpenLayers3 preview

And here is the same map in Leaflet with the added bonus of a nice address search bar which can be added automatically as well:

Leaflet preview

Leaflet preview

The workflow is really straight forward: select the desired layers and popup settings, pick some appearance extras, and then don’t forget to hit the Update preview button otherwise you might be wondering why nothing happens ;)

I’ll continue testing these plugins and am looking forward to seeing what features the future will bring.


What went on at FOSS4G 2015?

Granted, I could only follow FOSS4G 2015 remotely on social media but what I saw was quite impressive and will keep me busy exploring for quite a while. Here’s my personal pick of this year’s highlights which I’d like to share with you:

QGIS

Marco Hugentobler at FOSS4G 2015 (Photo by Jody Garnett)

Marco Hugentobler at FOSS4G 2015 (Photo by Jody Garnett)

The Sourcepole team has been particularly busy with four presentations which you can find on their blog.

Marco Hugentobler’s keynote is just great, summing up the history of the QGIS project and discussing success factor for open source projects.

Marco also gave a second presentation on new QGIS features for power users, including live layer effects, new geometry support (curves!), and geometry checker.

There has also been an update to QTiles plugin by NextGIS this week.

If you’re a bit more into webmapping, Victor Olaya presented the Web App Builder he’s been developing at Boundless. Web App Builder should appear in the official plugin repo soon.

Preview of Web App Builder from Victors presentation

Preview of Web App Builder from Victors presentation

Geocoding

If you work with messy, real-world data, you’ve most certainly been fighting with geocoding services, trying to make the best of a bunch of address lists. The Python Geocoder library promises to make dealing with geocoding services such as Google, Bing, OSM & many easier than ever before.

Let me know if you tried it.

Mobmap Visualizations

Mobmap – or more specifically Mobmap2 – is an extension for Chrome which offers visualization and analysis capabilities for trajectory data. I haven’t tried it yet but their presentation certainly looks very interesting:


FOSS4G specials at Packt and Locate Press

We are celebrating FOSS4G 2015 in Seoul with great open source GIS book discounts at both Packt and Locate Press. So if you don’t have a copy of “Learning QGIS”, “The PyQGIS Programmer’s Guide”, or “Geospatial Power Tools” yet, check out the following sites:

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