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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