Hi Luca,
I haven't followed the discussion in detail, but you could use
https://gdal.org/programs/gdallocationinfo.html
to read out the values from your resampled raster.
The elevation differences between high and coarse resolution DEMs
strongly depend on the relief in the area of investigation. So the
differences between 25m and 5000m DEMs might be quite significant. Maybe
better query the path on the high resolution and then smooth the profile
afterwards (to keep min/max values for example).
Another approach would be to resample your high res DEM with the min/max
resampling options of
https://gdal.org/programs/gdalwarp.html
and thus create low res DEMs with the extreme values.
Best regards,
Volker
On 12/28/21 20:51, Luca Bertoncello wrote:
Am 28.12.2021 um 04:54 schrieb Alan Snow:
After some thought, you may achieve what you want by resampling the file
to a 5km grid size with the Resampling.max option:
https://rasterio.readthedocs.io/en/latest/topics/resampling.html
https://rasterio.readthedocs.io/en/latest/api/rasterio.enums.html#rasterio.enums.Resampling.max
You can then store the centroid of the grid cell and the value in a
database.
So, maybe I got something...
I started with the EU DEM data from
https://land.copernicus.eu/imagery-in-situ/eu-dem/eu-dem-v1.1?tab=download
Then I created a VRT file of a part of these data, about what I need
(later I'll refine the sampling):
gdalbuildvrt -tr 25 25 -tap -te 3000000 1000000 8000000 6000000 r.vrt
../eudem/*.TIF
and then I resample the data saving all in a TIFF file:
gdalwarp -tr 5000 5000 r.vrt ../x/x.tif
Now I have a TIFF file with a resolution of 5x5 km (I hope):
$ gdalinfo -mm x.tif
....
Origin = (3000000.000000000000000,6000000.000000000000000)
Pixel Size = (5000.000000000000000,-5000.000000000000000)
Metadata:
.....
Do I am right until now?
I checked some known location (airports) and I see the elevation from
the 25 meter precision VRT file is better (of course) but the elevation
from the 5 km precision TIFF file is quite accurate, with a difference
of less than 10 meter. To create a vertical profile using during the
flight 10 meter are damned good.
Now I have to extract the data and save them in a SQLite file...
And I don't know how to do it per Script... :(
Any help?
Or maybe there are a Java-Library to using in Android to read the TIFF file?
Thanks
Luca Bertoncello
([email protected])
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