[gdal-dev] false easting and northing units

Thu Jan 25 08:08:10 PST 2024

Even,
Thanks for the explanation and tips. I'm not clear on how setting to 26988
(Michigan North meters) would help. If I do a gdal_translate with that, it
shows as being in New Zealand, just as Arc had done. It would certainly
make lots more sense to actually put the data in a standard projection that
has an EPSG code (meters or international feet), but that gets back to the
embarrassing tale. It may well be that I'll have to force GeoTiff 1.0. I
think there are other software packages that haven't caught up. Even when
they do catch up, I've come across people running 15 year old CAD software
and complaining about the DXF version GDAL produces.

Thanks to the whole team for the work you do to maintain GDAL.

Kirk

On Thu, Jan 25, 2024 at 10:47 AM Even Rouault <even.rouault at spatialys.com>
wrote:

> Kirk,
>
> perhaps you could try using -a_srs EPSG:26988+6360 instead of a full WKT.
> That way GDAL will *not* write the projected parameter definitions, but
> just reference the horizontal and vertical CRS codes:
>
> Geotiff_Information:
>    Version: 1
>    Key_Revision: 1.1
>    Tagged_Information:
>       ModelTiepointTag (2,3):
>          0                 0                 0
>          440720            3751320           0
>       ModelPixelScaleTag (1,3):
>          60                60                1
>       End_Of_Tags.
>    Keyed_Information:
>       GTModelTypeGeoKey (Short,1): ModelTypeProjected
>       GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
>       GTCitationGeoKey (Ascii,46): "NAD83 / Michigan North + NAVD88 height
> (ftUS)"
>       ProjectedCSTypeGeoKey (Short,1): PCS_NAD83_Michigan_North
>       VerticalCSTypeGeoKey (Short,1): Code-6360 (NAVD88 height (ftUS))
>       End_Of_Keys.
>    End_Of_Geotiff.
>
> Even
> Le 25/01/2024 à 16:17, Even Rouault via gdal-dev a écrit :
>
> Kirk,
>
> this is a complicated story indeed... What changed since
> https://trac.osgeo.org/gdal/changeset/31405 is that OGC GeoTIFF 1.1 was
> published, which mostly fixes issues with vertical CRS, which your CRS
> uses. So by default GDAL 3.1 or later, when seeing a CompoundCRS write it
> as GeoTIFF 1.1, and this new GeoTIFF version was the opportunity to remove
> writing the ProjLinearUnitsInterpCorrectGeoKey=3059 hack, since using
> GeoTIFF 1.1 is a way to indicate that you're implementing correctly the
> standard.
>
> If you force writing GeoTIFF 1.0 by adding -co GEOTIFF_VERSION=1.0, GDAL
> will write the ProjLinearUnitsInterpCorrectGeoKey when needed, and listgeo
> will show the "Unknown-3059 (Short,1): Unknown-1" geotiff key.
>
> To know if a Geotiff is 1.0 or 1.1 with listgeo , look at the Key_Revision
> in the 3rd line which will be 1.0 or 1.1
>
> So I assume ArcPro doesn't specifically implement 1.1. Either they
> implement GeoTIFF themselves, or they use GDAL < 3.1 that hasn't GeoTIFF
> 1.1 explicit support
>
> Even
> Le 25/01/2024 à 15:24, Kirk Waters - NOAA Federal via gdal-dev a écrit :
>
> Hi,
> I've run across an odd issue with GeoTIFFS using custom projections
> written by GDAL and their interpretation in ArcPro. The specific case is
> doing a projection for Michigan State Plane North using U.S. survey feet.
> [insert embarrassing tale of another US agency wanting to always use
> survey feet regardless of state legislation or that the federal government
> has been officially metric for a long time]. For a file that should land in
> the Michigan upper peninsula, ArcPro puts it in New Zealand. It appears the
> issue is that Arc is interpreting the false easting as meters instead of
> survey feet. If I do a define projection in ArcPro and make a custom
> projection, it lands in the right place.
>
> I used an old listgeo from the geotiff library to look at the tags both in
> the original file and a copy that had define projection applied to see what
> was different. They looked essentially the same, including having the same
> value for the false easting. However, the Arc version had an extra tag
> (3059) that wasn't in the GDAL produced one. An internet search turned up this
> 13-year old GDAL issue <https://trac.osgeo.org/gdal/ticket/3901>. If I
> understand it correctly, a bug in GDAL was found that always used meters
> for the false easting and northing. In addition to fixing that, a tag
> (3059) was added to indicate this was fixed so software could differentiate
> broken GDAL output from new output. It looks like Arc is looking for this
> tag and if it's not there, false easting is assumed to be meters.
>
> A few questions, assuming I interpreted that issue correctly:
> 1) Why is gdal not adding that 3059 tag? (GDAL command used is below)
> 2) If it's only supposed to be relevant to GDAL written files, why is Arc
> writing it?
> 3) How do I get GDAL to add the tag?
>
> Command used in file creation:
> gdal_translate -a_srs 'COMPD_CS[PROJCS["NAD83 / Michigan
> North",GEOGCS["NAD83",DATUM["North_American_Datum_1983",SPHEROID["GRS
> 1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY["EPSG","6269"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4269"]],PROJECTION["Lambert_Conformal_Conic_2SP"],PARAMETER["standard_parallel_1",47.08333333333334],PARAMETER["standard_parallel_2",45.48333333333333],PARAMETER["latitude_of_origin",44.78333333333333],PARAMETER["central_meridian",-87],PARAMETER["false_easting",26246666.6666667],PARAMETER["false_northing",0],UNIT["US
> survey
> foot",0.304800609601219],AXIS["X",EAST],AXIS["Y",NORTH]],VERTCRS["NAVD88
> height (ftUS)",  VDATUM["North American Vertical Datum 1988"],
>  CS[vertical,1],  AXIS["gravity-related height (H)",up],  LENGTHUNIT["US
> survey foot",0.304800609601], ID["EPSG",6360]]]' -co TILED=YES -co
> COMPRESS=DEFLATE -co PREDICTOR=3 -co BIGTIFF=IF_SAFER input.tif output.tif
>
> Kirk Waters, PhD
> NOAA Office for Coastal Management
> Applied Sciences Program
> coast.noaa.gov/digitalcoast
>
>
>
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> My software is free, but my time generally not.
>
>
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>
>
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