Thanks Even,
you are correct about the tag number (I sent the incorrrect one).
I have provided a sample tif and some other descriptions of the issue 
here:bad_geotiff - Google Drive

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| 
|  | 
bad_geotiff - Google Drive


 |

 |

 |


The three files there are the following:1.  A bad tiff (this is slightly 
smaller; they are all pretty big).2.  A GDAL info dump (survey feet is almost 
at the bottom)3. A PDF with an explanation of the issue
thanks for your help.Conrad


    On Thursday, March 21, 2024 at 04:50:19 PM EDT, 
gdal-dev-requ...@lists.osgeo.org <gdal-dev-requ...@lists.osgeo.org> wrote:  
 
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Today's Topics:

  1. USGS 3DEP (3D Elevation Program) - feet should be metres, how
      can I fix this? (Conrad Bielski)
  2. Re: USGS 3DEP (3D Elevation Program) - feet should be metres,
      how can I fix this? (Even Rouault)


----------------------------------------------------------------------

Message: 1
Date: Thu, 21 Mar 2024 20:45:27 +0000 (UTC)
From: Conrad Bielski <conrad_biel...@yahoo.com>
To: "gdal-dev@lists.osgeo.org" <gdal-dev@lists.osgeo.org>
Subject: [gdal-dev] USGS 3DEP (3D Elevation Program) - feet should be
    metres, how can I fix this?
Message-ID: <1045195440.383478.1711053927...@mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

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.

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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------------------------------

Message: 2
Date: Thu, 21 Mar 2024 21:49:55 +0100
From: Even Rouault <even.roua...@spatialys.com>
To: Conrad Bielski <conrad_biel...@yahoo.com>,
    "gdal-dev@lists.osgeo.org" <gdal-dev@lists.osgeo.org>
Subject: Re: [gdal-dev] USGS 3DEP (3D Elevation Program) - feet should
    be metres, how can I fix this?
Message-ID: <7832c1d9-61ce-41b0-b524-2f00859c8...@spatialys.com>
Content-Type: text/plain; charset="utf-8"; Format="flowed"


Le 21/03/2024 ? 21:45, Conrad Bielski via gdal-dev a ?crit?:
> 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
>
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev@lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/gdal-dev

-- 
http://www.spatialys.com
My software is free, but my time generally not.
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