[gdal-dev] Hillshade | Raster Band Rendering

[Joaquim Luis]

>
> My objective is to create a hillshaded color-relief image of a DEM using  
> commandline/programmatic means only, so the process >can be automated  
> and combined within an existing GMT/GDAL workflow.

If your workflow includes GMT that you have a reach panoply of methods to  
do shade illuminations. See man pages of grdgradient and grdhisteq.

Joaquim

>
>
> Currently, I can generate both hillshaded and color-relief rasters using  
> gdaldem and combine them with Mapnik (using opacity) to >generate a my  
> final rendered image. However, this process will use the min-max values  
> in the grayscale hillshaded image.
>
>
> However, I can achieve an improved or sharper hillshaded image when I  
> manually use QGIS to further process the hillshaded image >by:
>
> 1. Adding the hillshaded raster to QGIS, which applies by default the  
> 'Cumulative count cut 2% - 98%' style.
>
> 2. Then export the hillshaded raster (with the cumulative count style  
> applied) as a “Rendered Image”.
>
>
> I have annotated a screenshot here  
> https://www.dropbox.com/s/ftzk7j2bmznuvjn/raster_band_rendering.png?dl=0  
> hopefully >illustrating the
>
> 1.    Improved hillshaded raster output from QGIS ('Cumulative count  
> cut) compared with,
> 2.    gdal+mapnik output (using min-max)
>
> So, is there an approach using gdal (or similar command-line tool/app)  
> to achieve the “improved” hillshaded raster without the >“manual” QGIS  
> step?
>
>
> As I see it, my options are:
>
> 1. Use gdalinfo with the “-hist” option to export the histogram of the  
> hillshaded raster. I guess then I could maybe calculate the 2% >and 98%  
> percentile(?) values and then manipulate the raster values using  
> gdal_calc.py or something else.  However, I’m no >statistician, so hoped  
> there would be an out of the box solution?!
>
> 2. Maybe, I could use the python api for QGIS to import the hillshade,  
> render, style and export back out. I’m sure this is possible, >but would  
> require an additional python script.
>
> 3. Use another library or framework to achieve either of the above. I’ve  
> researched python’s numpy library, which maybe I could do >the  
> percentage calculation directly on the raster. Again, potentially tricky  
> learning curve there…
>
>
> Any help or advice would greatly appreciated. If any help, the data I’m  
> using is here  
> https://www.dropbox.com/s/v0peaa3rzaqbhen/>raster_band_rendering.zip?dl=0
>
>
> Cheers
>
>
>> Gareth
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