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Sat Feb 28 11:25:08 2015

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QGIS Planet

Dica para ajustar posição de símbolos em QGIS | Hack to adjust map symbols location in QGIS

De quando em vez aparecem-me zonas com demasiado símbolos no mesmo local, e pensei como seria fantástico se os pudesse arrastar para um local mais conveniente sem ter de alterar as suas geometrias, tal como é possível fazer com as etiquetas. Esse pensamento deu-me a ideia base para a dica que vou demonstrar.

Now and then I get too many map symbols (points) in the same place, and I thought how nice it would be if we could drag n’ drop them around without messing with their geometries position, just like we do with labels. That thought gave me an idea for a cool hack.

Escolha a sua camada de pontos e comece por criar dois novos campos chamados symbX e symbY (Tipo: Decimal; Tamanho: 20; precisão: 5). No separador “Estilo” das propriedades da camada, defina para cada nível do seu símbolo o seguinte: Escolher “unidade do mapa” como a unidade para as opções de afastamento; Usar a seguinte expressão na opção afastamento das propriedades definidas por dados.

Choose your point layer and start by creating two new fields called symbX and symbY (Type: Decimal number; Size: 20; Precision: 5). Now go the layer properties and in the Style tab edit your symbol. For each level of your symbol select “map units” as the offset units, and set the following expression in the offset data define properties option:


CASE WHEN symbX IS NOT NULL AND symbY IS NOT NULL THEN
    tostring($x - symbX) + ',' + tostring($y - symbY)
ELSE
    '0,0'
END

Screenshot from 2015-02-22 18:18:43

Tenha atenção que, se as coordenadas do seu mapa tiver valores negativos, será necessário uma pequena alteração ao código. E. g., se tiver valores negativos em X deverá usar-se  antes a expressão “tostring(symbX -$x)”.

Beware that if your coordinates have negative values you need to adapt the code. E.g., If you have negative values in X you should use “tostring(symbX -$x)” instead.

De forma temporária coloque etiquetas na sua camada usando um texto pequeno (eu usei o ‘+’ (sinal de mais) centrado e com um buffer branco) e defina as coordenadas X e Y dos propriedades definidadas por dados usando os campos symbX e symbY,

Now, temporarly  label your layer with a small convenient text (I used a centered ‘+’ (plus sign) with a white buffer) and set its coordinates to data defined using the symbX and symbY Fields.

Screenshot from 2015-02-22 22:42:07

A partir desse momento, quando usar a ferramenta de mover etiquetas, não só alterará a posição da etiqueta, mas também a do próprio símbolo! Fantástico, não?

From this point on, when you use the move label tool, not only the label position change but also the actual symbol! Pretty cool, isn’t it?

anim

Note que as geometria dos elementos não são alteradas durante o processo. Para além disso, lembre-se que neste caso também poderá adicionar linhas de guia para ligar os símbolos à posição original do ponto.

Notice that the features geometries are not changed during the process. Also, remember that in this case you can also add leading lines to connect the symbols to the original position of the points.


QGIS course at AfQUA

Kartoza has just wrapped up a three-day Introduction to QGIS course that we gave pro bono at The African Quaternary: Environments, Ecology and Humans conference in Cape Town (AfQUA2015). Thank you to Kelly Kirsten from the local organising committee at the University of Cape Town for inviting us. Admire Nyakudya presented to about fifteen conference delegates from around the world. Attendees ran QGIS 2.6.1 on their own notebooks on the operating system of their choice. Some already use QGIS, some were experiencing QGIS for the first time and some some wanted to compare it with ArcGIS. The course content was guided largely by the QGIS training manual but as we usually do, adapted for the requirements, interests and pace of the class.

 

Kartoza QGIS class at AfQUA 2015

Admire presenting QGIS workshop at AfQUA

Publishing interactive web maps using QGIS

We all know that QGIS is great for designing maps but did you know that QGIS is also great for interactive web maps? It is! Just check out qgis2leaf and qgis2threejs.

To give these two plugins a test run and learn some responsive web design, I developed a small concept page presenting cycle routes in 3D.

Screenshot 2015-01-31 22.20.15

Qgis2leaf makes it possible to generate Leaflet maps from QGIS layers. It provides access to different background maps and it’s easy to replace them in the final HTML file in case you need something more exotic. I also added another layer with custom popups with images but that was done manually.

Daten CC-BY-3.0: Land Kärnten - data.ktn.gv.at

The web maps use data CC-BY-3.0: Land Kärnten – data.ktn.gv.at

Qgis2threejs on the other hand creates 3D visualizations based on three.js which uses WebGL. (If you follow my blog you might remember a post a while back which showcased Qgis2threejs rendering OSM buildings.)

This is a great way to explore elevation data. I also think that the labeling capabilities add an interesting touch. Controlling the 3D environment takes some getting used to, but if you can handle Google Earth in your browser, this is no different.

Image of Heiligenblut by Angie (Self-photographed) (GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)), via Wikimedia Commons

Image of Heiligenblut by Angie (Self-photographed) (GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)), via Wikimedia Commons


How to load a QGIS project in python

Today in a project we are working on we wanted to load a QGIS project. It takes  surprisingly few lines of code to make a small standalone application that loads a project and then shows it as a map in a window like this:

QGIS project in a standalone app

 

Here is the code I wrote to produce this:

The main bit of magic is the QgsLayerTreeMapCanvasBridge class which will convert your project into a layer tree so that the layers appear in the canvas. If you ever need to make a standalone python application with a nice map in it, consider using the QGIS API to do it!

A quick hack to select all multipart features in QGIS

Today we wanted to find all the multipart features in this layer:

The layer that needs multipart features identified

Here is a quick hack I did in QGIS to find them:

Just make sure that a vector layer is active in the layer list, paste the above code into the python console and all multipart features will be highlighted for you.

After running the above script, multipart features are hightlighted.

A line gradient style hack

Today’s post was motivated by a question over on gis.stackexchange, basically: How to draw a line with a gradient?

The issue we have to deal with is there is no gradient line style yet … But there are polygon gradient fills. So we can buffer the line and style the buffers. It’s a bit of an exercise in data-defined styling though:

Screenshot 2015-01-11 22.49.41

Before creating the buffer layer, we need to add the coordinates of the line start and end node to the line attributes. This is easy to do using the Field Calculator functions xat and yat, for example xat(0) for the x coordinate of the start node and yat(-1) for the y coordinate of the end node.

Screenshot 2015-01-11 22.41.37

Then we can buffer the lines and start styling the buffers. As mentioned, we’ll use the Gradient fill Symbol layer type.

Screenshot 2015-01-11 22.49.54

The interesting part happens in the Data-defined properties. The start and end colors are computed from the measurement values from_m and to_m. Next, it’s important to use the feature coordinate mode because this will ensure that the coordinate system for the color gradient is based on the feature extent (with [0,0] in the upper left corner of the feature bbox).

Once that’s set up, we can compute the gradient start and end positions based on the line start and end node locations which we added to the attribute table in the beginning. If you’re wondering why Reference point 1 y is based on to_y (y coordinate of the line end point) rather than from_y, it’s due to the difference in coordinate origins in the geometry and the color gradient coordinate space: [0,0] is the lower left corner for the geometries but the upper left corner for the color gradient.

Screenshot 2015-01-11 22.42.35

As the title suggests, this is a really hackish solution for gradient line symbols. It will only provide reasonable results for straight – or close to straight – lines. But I’m very confident that we’ll have a real gradient line style in QGIS sooner or later.


QGIS – live layer effects Kickstarter update

Here’s another quick video demonstration of the latest developments in layer effects – effects on polygon and polyline layers, and outer glow effects:

Time is running out to fund this campaign and make this work happen… Please donate via Kickstarter!

I’ve also been asked what will happen if funding exceeds the Kickstarter goal? Well, if this happens, the extra funds will be used to add additional layer effects to QGIS. Next up will be inner glow, inner shadow and color modification effects.

Use of the Flemish geographical data portal “Geopunt” in QGIS

Geopunt website Geopunt is the central portal for geographical data of the Flemish government. Beside an online viewer, a catalogue is available from where data can be downloaded. A lot of these data are free to download (e.g. orthophotos), other data is available depending on your user profile (e.g. soil map) Download through the Geopunt4Qgis […]

How to: watercolor pastel style in QGIS

Today’s post is a follow-up to a recent map experiment which I published in the QGIS Flickr group. It’s basically an inverted Stamen Toner style with an image in the map composition background instead of a solid color (similar to the approach described for vintage maps):

That’s nice but with this approach we only get to enjoy the complete design in the print composer but not in the main window. So what other options do we have? – SVG fills to the rescue!

But first we need a suitable SVG with this nice pastel style. I used Gimp to create a seamless version of the pastel image and then embedded the image in an SVG using Inkscape:

LT_RemixedChalkPastel_snakk_seamless

In QGIS, this SVG can now be used in any SVG fill. It’s important to set the Texture width setting to a quite high value when working with SVGs containing big textures, otherwise the images will be rendered very small and the repeating patterns will be very obvious.

Screenshot 2015-01-04 17.49.11

Once the background is in place, we can add the line work and labels. The roads are white with black outlines for bridges which – together with the Lighten blending mode – produce the desired effect:

Screenshot 2015-01-04 17.37.33


Top10 QGIS Planet posts 2014

It’s the end of December and time to recap 2014. Therefore, I decided to have a look at what this year has brought us. There were plenty of great posts for both casual and power users as well as developers. Here is my pick of the top 10 posts from the QGIS Planet blog aggregator.

  1. Tons of colour improvements! (Nyall Dawson)
  2. The QGIS Field calculator is dead. Long live the Field calculator bar (Nathan Woodrow)
  3. Why QGIS Class Names Start with Qgs (Gary Sherman)
  4. Atlas Previews (Nyall Dawson)
  5. QGIS atlas on non geometry tables (Nathan Woodrow)
  6. Gradient Fills (Nyall Dawson)
  7. What are all these QGIS file types? Why do I need them (Nathan Woodrow)
  8. Getting Started Writing QGIS Python Plugins (Peter Wells)
  9. QGIS Layer Tree API (Martin Dobias)
  10. Shapeburst fill styles (Nyall Dawson)

More great features and posts are sure to come next year. For example, Nyall is currently running a campaign on Kickstarter to add Live Layer Effects such as drop shadow effects to QGIS. Please support it if you can.


Kickstarter Alert – Live Layer Effects for QGIS

QGIS is well regarded for its fantastic cartographic abilities – it’s got a huge range of symbology styles and options which can be used to style your maps. But there’s more we can do to push this even further.

One long requested cartographic feature has been for live drop shadows on layers. Why stop there? Why not inner and outer glow effects and live blur effects? Just imagine the cartographic possibilities if this functionality was available from within a GIS, and didn’t require exporting maps to external editors…

I’ve launched a Kickstarter project to fund implementing live layer effects like this within QGIS. Please consider donating or spreading the word if you’d find this feature useful!

Setting up a Fedora 21 QGIS Workstation

I have been a long time Ubuntu user (I have actually been using it since Ubuntu 4.10 ‘Warty Warthog’) – the first official release. The advent of Ubuntu saw an end to my distro hopping whilst looking for the ‘perfect linux distro’.

Recently though, Ubuntu has been losing momentum in my opinion – especially in terms of supporting the latest Gnome desktop editions and catering for those of us who like to use a leading edge platform for our developer workstations. I was particularly curious to see if QGIS runs nicely under Wayland, the next-generation graphics environment for Linux.

I have been using docker heavily for the last year and have come to the point where I feel that the underlying Linux flavour is less important since I can fairly arbitrarily deploy applications in docker containers using whichever flavour of Linux inside the container is most convenient.

Thus I decided to try and see how easy it would be to get Fedora 21 installed on my MacBook 13″ Laptop which was running Ubuntu quite nicely until now. In the Gist below, I detail the various installation steps I took to get my standard suite of applications installed. These include:

  • docker
  • QGIS compilation build chain
  • PyCharm 4
  • Shutter
  • Skype
  • QtCreator / QtDesigner etc.
  • btsync
  • Google Chrome
  • vlc and assorted video codecs
  • keepassx
  • Elegance gnome theme (must-have if you use Gnome!)

 

Workspace 1_130

I will keep the above Gist updated as I tweak my configuration, but by and large the migration to Fedora has been fairly painless and I am enjoying working on the latest Gnome desktop. I was able to replicate pretty much all of the application stack I ran on Ubuntu, though in some cases the setup & installation of applications was a little more complex than on Ubuntu, and in one case (btsync-gtk-gui) I have not yet found a binary installation package.

2nd edition of Learning QGIS

It’s my pleasure to announce that the updated and extended 2nd edition of Learning QGIS is available now.

I also want to take this opportunity to thank everyone who made the 1st edition such a great success!

This second edition has been updated to QGIS 2.6 and it features a completely new 6th chapter on Expanding QGIS with Python. It introduces the QGIS Python Console, shows how to create custom Processing tools, and provides a starting point for developing plugins.

Overall, the book has grown by 40 pages and the price of the print version has dropped by 3€ :-)

Happy QGISing!

2031OSos_mockupcover_normal_0


Mozilla Stumbler layer: loading TMS and XYZ tilelayers in QGIS

Mozilla Location Service (MLS) layer Personally I’m very interested in the Mozilla Location Service (MLS), I wrote an earlier article about it on my work (Zuidt.nl) blog. Key in this project is that both locations of wifi points and cell towers are crowdsourced and put in a open database, so everybody can use that data […]

QGIS 2.6 user guide released

The QGIS documentations team has released an updated version of the user guide:

qgisdocs26

I’d like to encourage everyone to have a look and explore the content, for example the great tips in the Actions menu section:

action_dialog


QGIS 2.6.1 and QGIS 2.6 Documentation Released

QGIS 2.6.1 Just a short notice that the QGIS project (silently) released QGIS 2.6.1, a bug fix release for the latest stable version of QGIS 2.6 Brighton. Some notable fixes include: - composer stuff which was not working ok - not all attribute columns showing in attribute table - metasearch (CSW plugin) was not working […]

Analyzing regional income differences

On my quest to create test data for spatial statistics, I’ve discovered income data for Austria per municipality on a news paper website:

Screenshot 2014-11-29 23.06.46

For further analysis, I decided to limit the area to Vienna and Lower Austria. Since the income data included GKZ “Gemeindekennzahl” IDs, it was possible to join them to municipalities extracted from OpenStreetMap using QuickOSM for QGIS. GRASS v.clean was used to clean the vector topology to the point where PySAL was able to compute spatial weights.

Using PySAL, I then computed income clusters: blue regions represent low clusters while red regions represent high clusters …

Municipality border data (c) OpenStreetMap and contributors Income data source: Statistik Austria via derStandard

Municipality border data (c) OpenStreetMap and contributors
Income data source: Statistik Austria via derStandard

The results show a statistically significant cluster of low income in the north west, in the area called Waldviertel, as well as a cluster of high income containing many of the municipalities surrounding Vienna, an area often referred to as the “Speckgürtel” (“bacon belt”).


Releasing TimeManager 1.2

Today, I’ve released TimeManager 1.2 which adds support for additional time formats: DD.MM.YYYY, DD/MM/YYYY, and DD-MM-YYYY (thanks to a pull request by vmora) as well as French translation (thanks to bbouteilles).

TimeManager now automatically detects formats such as DD.MM.YYYY

TimeManager now automatically detects formats such as DD.MM.YYYY

But there is more: the QGIS team has released a bugfix version 2.6.1 which you can already find in Ubuntu repos and the OSGeo4W installer. Go get it! And please support the bugfix release effort whenever you can.


How to build and debug QGIS with QtCreator

Here is how I build QGIS with QtCreator under ubuntu 14.04

A new QGIS tool (based on ogr2ogr) to import vectors in PostGIS, the fast way

In QGIS there are many tools that can be used to import vectors inside a PostGIS database, each one has pros and cons: SPIT core plugin: available since long ago but now seems to be a unmaintained tool and therefore will be probably removed in a future QGIS release. It  has the advantage to allow […]

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