Task #612
openDEM Evaluation
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Description
We started working with the DEM and will use this issue as a place to record any observations (unexpected values, artefacts, etc.)
Files
Updated by Adam Wilson over 11 years ago
- File min_gdalinfo_s.txt min_gdalinfo_s.txt added
Giuseppe Amatulli pulled out the minimum values for all tiles and found a few strangely large negative numbers in some. I haven't gone to cross check these with real areas below sea level, but it might be worth looking into. See attached for the full list, but here are a few for example:
-600.000 dem/tiles/Smoothed_N65W040.bil
-599.000 dem/tiles/Smoothed_N65W045.bil
-599.000 dem/tiles/Smoothed_N80W045.bil
-597.000 dem/tiles/Smoothed_N60W050.bil
-597.000 dem/tiles/Smoothed_N65W050.bil
-591.000 dem/tiles/Smoothed_N80W055.bil
-588.000 dem/tiles/Smoothed_N80W060.bil
-582.000 dem/tiles/Smoothed_N75W065.bil
-571.000 dem/tiles/Smoothed_S55W075.bil
-563.000 dem/tiles/Smoothed_N70W040.bil
Updated by Adam Wilson over 11 years ago
Giuseppe Amatulli also reported:
"Some data have the following gdalinfo -mm results
Band 1 Block=6000x1 Type=Int16, ColorInterp=Undefined
Min=0.000 Max=0.000 Computed Min/Max=0.000,0.000
Minimum=0.000, Maximum=0.000, Mean=0.000, StdDev=0.000
NoData Value=-32768
other just
Band 1 Block=6000x1 Type=Int16, ColorInterp=Undefined
Computed Min/Max=-8.000,1338.000
NoData Value=-32768
this is not an issues in the pixel value but just in the metadata.
It would be better to have the same;
It is better the second option because the firs is not easy readable
by gdal library."
Updated by Natalie Robinson over 11 years ago
This is really great, and THANK-YOU, all, for exploring this dataset!!
As I suspected, the very low values in those first 10 tiles listed above are anomalies that carried through from the source DEMs. Our low values are even, in a few cases, slightly better than the source data minimums (only by about a meter).
I also delved further into one of the ASTER tiles to pinpoint the original raw tile (in 1 x 1 degree, 30m) where this occurred. For our tile: EarthEnv-DEM90_N70W040, the bad value comes from the ASTER GDEM2 tile: ASTGTM2_N70W038. In fact, through our processing this anomalous value even became slightly less negative (-565 in the raw ASTER tile, -563 in our tile).
I'll follow up on the metadata issue soon, and recreate tiles if needed. There is a good chance that the 0's for all stats occur because the tile contains only ocean (which has a value of 0 in our dataset).
Again- thanks, and keep 'em coming!