By
2012-01-19
GIS, QGIS
10 Comments

A Guide to Beautiful Reliefs in QGIS

This week Sourcepole released a new addition to the Raster Terrain Analysis plugin: a sophisticated Relief tool. (More info in their announcement) This plugin is shipped with QGIS (developer version, not in 1.7.3 release) by default but you might have to activate it in Plugin Manager:

The plugin dialog is quite self-explanatory. You can chose the elevation file, output path and any of the numerous raster formats. The z factor is a bit more mysterious. We will have a look at that in a second. The rest of the dialog is the relief color editor. Pressing Create automatically will give you a color gradient to start with.

Relief tool dialog

But what’s the z factor good for?

I’ve tried a few different settings using free NASA SRTM data and it seems that higher values lead to a smoother relief (Please ignore the water areas):

z factor = 100
z factor = 1000
z factor = 10000
z factor = 50000
z factor = 100000

Update:

As Marco noted in the comments: The z factor is used if the x/y units are different from the z unit.

  • If everything is in meters, use z factor 1.0 (default).
  • If x/y is in degree and z in meters, use z factor 111120.
  • If x/y degree and z is feet, use z factor 370400.

In the example above SRTM rasters are in WGS84 with heights in meters. That’s why the result using a z factor of 100000 looks so good.

In my opinion the results look great even with the coarse SRTM dataset I used. Looking forward to all the great QGIS maps we will see in the future.

10 comments
  1. Henrik said:

    Nice. Z is usually elevation/altitude, hence it might be the height of the sun…

  2. Marco said:

    Hi Anita

    The z-factor is used if the x/y units are different to the z-unit. If everything is in meters, use z-factor 1.0 (default). If x/y is in degree and z in meters, use z-factor 111120. If x/y degree and z is feet, use z-factor 370400.

    • underdark said:

      Thank you for the clarification Marco!

  3. simbamangu said:

    This looks like a terrific extension … yet another thing to sway people who won’t leave ArcGIS! Doesn’t seem to be available on the Mac yet though (old dialogue only and plugin updates don’t find anything new).

    Do the export and import options work with XML files for custom color ramps?

    • underdark said:

      As far as I know the plugin is only available in the latest developer version. If I’m right there is no such thing for Mac, so Mac users will have to wait or use a VM.

      The XML format used here seems to be a custom one unfortunately. It might we worth asking the developers for support for other formats that are already in use in QGIS.

  4. Gerardo Jiménez Delgado said:

    Nice entry, nevertheless I can not find the options you mention. I tried to upgrade the plugin, but I can not find it, even if I have enabled 3rd party repositories and experimental plugins. Any Idea
    I am using Qgis 1.73 standallone in Win7 32b
    Thanks before hand

    Gerardo

    • underdark said:

      You need the developer version. I don’t know if it will be back-ported to a possible 1.7.4 release

      • Gerardo Jiménez Delgado said:

        Thanks!!

  5. MapserverSA said:

    Looks great but can’t find it in the Repositories. I have the Sourcepole Rep loaded but its not in there either. Can anyone tell me where it is???

    • underdark said:

      You don’t have to and cannot get it from any repository.
      As noted above:
      “This plugin is shipped with QGIS (developer version, not in 1.7.3 release) by default but you might have to activate it in Plugin Manager:”