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FOSSGIS Konferenz 2012 in Dessau

Die FOSSGIS und deutschsprachige Open Street Map Konferenz 2012 – die grösste deutschsprachige Anwenderkonferenz für Freie Geo-Informationssysteme und freie Geodaten – findet vom 20. bis 22. März 2012 an der Hochschule Anhalt in Dessau-Rosslau statt.

Sourcepole ist mit folgenden Vorträgen und Workshops vertreten:

Da mehr als 400 Teilnehmende erwartet werden, ist eine Registrierung bis zum 16. März 2012 notwendig. Das Anmeldeformular und andere organisatorische Informationen befinden sich auf der Konferenzseite.

Shaded relief maps with QGIS

Creating a shaded relief map from digital elevation data is a nice way to create a backround map for web mapping or other GIS work. Thanks to the know-how and the funding from the Swiss Humanitarian Aid Unit, QGIS now has a sophisticated function for relief map generation. The method is described in detail in an paper by Marc-André Bünzli. An important part of the method is the choice of the elevation colors. The QGIS plugin has the possibility to analyse the frequency distribution of the elevation values in the DEM and to propose color changes where significant changes in the histogram occure. It is of course also possible to modify the color scheme, to insert a completely different one in the dialog or to generat a shaded maps without color.

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As illustrated below, the relief map is composed by three components modulated onto the final map to give it a more three-dimensional appearance. These intermediate steps are shown here to get a better understanding of the method. In QGIS, the user directly gets the combination as a result.

  • The first component consists of a hillshade from north-west (300 degree) and an elevation color

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  • The second component is a hillshade and a gray value depending on the slope angle (darker is steeper). The hillshade angle of this second component differs to the first component by 15% to have better contrast in faces towards the light source. The second component is merged to the relief map with 30% weight.

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  • The third component consists of a hillshade from 270 degree and a yellow color in cells facing towards the light source. It is merged to the relief map with 10% weight

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And the final relief map looks like this:

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Raster resampling in QGIS

QGIS already offers a lot of possibilities to visualize raster data (contrast enhancement, color map, handling of transparent pixels, …) Last year, Radim Blazek refactored the raster provider interface and added on-the-fly reprojection support for rasters to QGIS. Very cool!

One of the few things currently missing in QGIS raster layer is the possibility to have other resampling types than nearest neighbour. The problem is that rasters appear pixelated when zooming further than the source raster resolution. So for applications like web mapping, it is important to interpolate the pixel colors and to have a broader display scale range for layers. In the last few weeks, I’ve added bilinear and cubic raster resampling to QGIS (thanks to Canton Solothurn for funding these activities!).

A lot of refactoring was necessary in the raster layer code to add resampling in a clean way. Therefore these changes are available in branch ‘raster_resampler’ of the QGIS github clone (<git://github.com/mhugent/Quantum-GIS.git>). It probably needs a longer period of testing to make sure every feature of the raster layer class still works properly.

The resampling option can be chosen in the raster properties dialog:

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And here is the effect for a three band color image.

Nearest neighbour:

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Bilinear:

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Cubic:

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And here for a palletted background map

Nearest neighbour:

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Bilinear:

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SMTP death penalty for Ebuyer.com

For an unknown reason Ebuyer.com was spamming me for years and wouldn’t take me out of their spam distributor. So now they’re blacklisted on the SMTP level. No more spam to any of us or any of our customers/domains.

mail:~# cat /etc/exim4/local_sender_blacklist 
*@*ebuyer.com

Bye bye Ebuyer spam