[gdal-dev] USGS 3DEP (3D Elevation Program) - feet should be metres, how can I fix this?

[Even Rouault]

Le 21/03/2024 à 21:45, Conrad Bielski via gdal-dev a écrit :
> Hello GDALers,
>
> I have a question about reading USGS 3DEP (3D Elevation Program) data. 
> Inside of this data, a GEOTIFF tag 42114 is provided which is causing 
> problems with datum shifts.

There's no such thing as a GEOTIFF tag 42114.

The closest tags are:

#define TIFFTAG_GDAL_METADATA 42112
#define TIFFTAG_GDAL_NODATA 42113

It would be helpuful if you could provide the file, or the result of a 
"tiffdump -m 1000 the.tif" and "listgeo the.tif" on it.

And was the .tif.aux.xml provided with the TIFF, or computed by GDAL. 
Because the information might come from it too.

>
> So when I use GDAL to compute the datum shifts, the tag is read and 
> interprets that the DEM is showing elevation in 'feet' while the DEM 
> is actually in metres. The DEMs are in fact in meter elevations and 
> meter UTM horizontal coordinates. This is obviously erroneously 
> integrated into the tag.
>
> So my question is whether anyone has come across this issue and found 
> a solution? Is there a way to edit the offending tag so that it is 
> correctly interpreted as metres instead of feet? Other potential 
> solutions so that GDAL interprets the elevation correctly?
>
> Thanks in advance for your help. I provide below the output of 
> gdalinfo which I hope could help with the offending info in bold.
>
> Have a great day,
> Conrad
>
>
>
>
> Driver: GTiff/GeoTIFF
> Files: 
> I:\v3_us_3dep\asheville\ashevilleUSGS_1M_17_x34y392_NC_Phase5_2018_A18.tif
>  I:\v3_us_3dep\asheville\ashevilleUSGS_1M_17_x34y392_NC_Phase5_2018_A18.tif.aux.xml
> Size is 10012, 10012
> Coordinate System is:
> PROJCRS["NAD83 / UTM zone 17N",
>     BASEGEOGCRS["NAD83",
>         DATUM["North American Datum 1983",
>             ELLIPSOID["GRS 1980",6378137,298.257222101,
>                 LENGTHUNIT["metre",1]]],
>         PRIMEM["Greenwich",0,
>             ANGLEUNIT["degree",0.0174532925199433]],
>         ID["EPSG",4269]],
>     CONVERSION["UTM zone 17N",
>         METHOD["Transverse Mercator",
>             ID["EPSG",9807]],
>         PARAMETER["Latitude of natural origin",0,
>             ANGLEUNIT["degree",0.0174532925199433],
>             ID["EPSG",8801]],
>         PARAMETER["Longitude of natural origin",-81,
>             ANGLEUNIT["degree",0.0174532925199433],
>             ID["EPSG",8802]],
>         PARAMETER["Scale factor at natural origin",0.9996,
>             SCALEUNIT["unity",1],
>             ID["EPSG",8805]],
>         PARAMETER["False easting",500000,
>             LENGTHUNIT["metre",1],
>             ID["EPSG",8806]],
>         PARAMETER["False northing",0,
>             LENGTHUNIT["metre",1],
>             ID["EPSG",8807]]],
>     CS[Cartesian,2],
>         AXIS["(E)",east,
>             ORDER[1],
>             LENGTHUNIT["metre",1]],
>         AXIS["(N)",north,
>             ORDER[2],
>             LENGTHUNIT["metre",1]],
>     USAGE[
>         SCOPE["Engineering survey, topographic mapping."],
>         AREA["North America - between 84°W and 78°W - onshore and 
> offshore. Canada - Nunavut; Ontario; Quebec. United States (USA) - 
> Florida; Georgia; Kentucky; Maryland; Michigan; New York; North 
> Carolina; Ohio; Pennsylvania; South Carolina; Tennessee; Virginia; 
> West Virginia."],
>         BBOX[23.81,-84,84,-78]],
>     ID["EPSG",26917]]
> Data axis to CRS axis mapping: 1,2
> Origin = (339993.999958705157042,3920005.999981591943651)
> Pixel Size = (1.000000000000000,-1.000000000000000)
> Metadata:
>   AREA_OR_POINT=Area
> Image Structure Metadata:
>   COMPRESSION=LZW
>   INTERLEAVE=BAND
>   LAYOUT=COG
>   PREDICTOR=3
> Corner Coordinates:
> Upper Left  (  339994.000, 3920006.000) ( 82d45'43.98"W, 35d24'38.21"N)
> Lower Left  (  339994.000, 3909994.000) ( 82d45'36.92"W, 35d19'13.36"N)
> Upper Right (  350006.000, 3920006.000) ( 82d39' 7.17"W, 35d24'43.82"N)
> Lower Right (  350006.000, 3909994.000) ( 82d39' 0.55"W, 35d19'18.95"N)
> Center      (  345000.000, 3915000.000) ( 82d42'22.15"W, 35d21'58.63"N)
> Band 1 Block=512x512 Type=Float32, ColorInterp=Gray
>   Min=669.509 Max=1604.949
>   Minimum=669.509, Maximum=1604.949, Mean=988.295, StdDev=159.804
>   NoData Value=-999999
>   Overviews: 5006x5006, 2503x2503, 1251x1251, 625x625, 312x312
> *Unit Type: US survey foot*
>   Metadata:
>     STATISTICS_APPROXIMATE=YES
>     STATISTICS_MAXIMUM=1604.9490966797
>     STATISTICS_MEAN=988.29463693706
>     STATISTICS_MINIMUM=669.50915527344
>     STATISTICS_STDDEV=159.80361228109
>     STATISTICS_VALID_PERCENT=100
>
>
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