[Qgis-developer] shaded relief plugin update

[Andreas Plesch]

Hello,

following up on a bug report, I added a couple lines to the shaded
relief plugin which replaces a nodata value with  the mean elevation
of the DEM if it is tagged valid. I uploaded the updated plugin as
version 2.3 to the plugin repository. Please give it a try. The way to
use it  is to define a no data value in the transparency tab. There
are no UI  changes in the plugin. For most of my test cases there was
no difference between shaded relief with and without nodata values.
This is because typically the slopes around the nodata values are
steep (even with the mean elev. in place), and aspect based shading is
used which does not depend much on slope. In order to see a difference
one has to increase clip values to 89 and 90, so only diffuse
reflection is used. In cases where the nodata value is some extreme
number replacing the extreme numbers with reasonable ones makes numpy
- used for all computations - happier.

It might be possible to put a NULL value in the cells of the shaded
relief where the DEM has a NULL value, masking the shaded relief.
Would that be desirable ? The main problem there is that the shaded
relief is 8bit, so one would have to give up a number. And I am not
sure if the geotiff driver supports NULL. On the other hand, it should
be possible to transfer nodata cells from one raster to another with
other available tools. Is that the case, perhaps with the raster
calculator ?

For proper nodata support numpy would need to support NULL values in
the gradient calculation which is not the case yet but apparently will
be in their next release (2.0.0).

Andreas