[gdal-dev] [PATCH v2] Support Mercator_2SP in GeoTIFF

Mon Nov 18 04:54:01 PST 2013

Hi Trent,

The chart  opens in ArcMap (ArcGIS 10.0) well, and it is in right
location (Seattle).

Relevant properties of the file as seen by ArcGIS:
Cell Size: 240.003787, 240.003787
Extent
Top:4143530.20898
Left: -9278434.53415
Right:  -9165872.75807
Bottom:  3984167.69444
Spatial Reference: Global Mercator
Linear Unit: Meter
false_easting: 0
false_northing: 0
central_meridian: 0
standard_parallel_1:  47.667
Datum: D_North_American_1983

I opened the file in FME Data Inspector (FME Desktop 2013 SP1) also.
It did not read the latitude of true scale from the
ProjStdParallel1GeoKey as you can see from the following parameters.
Therefore it places the chart to NE Georgia/NW South Carolina as if
the latitude of true scale was the Equator.

<FME Parameters>
Coordinate System Parameters
CS_NAME: _FME_0
DESC_NM: Global Mercator
DT_NAME: NAD83
PROJ: MRCAT
UNIT: METER

Datum Parameters
DESC_NM: NAD 1983, Alaska, Canada,Continental US,Mexico,Central America
ELLIPSOID: GRS1980
SOURCE: US Defense Mapping Agency, TR-8350.2-B, August 1993
USE: NAD83

Ellipsoid Parameters
DESC_NM: Geodetic Reference System of 1980
E_RAD: 6378137
P_RAD: 6356752.3141403478
SOURCE: Stem, L.E., Jan 1989, State Plane Coordinate System of 1983

OGC WKT Description
PROJCS["Global Mercator",
    GEOGCS["NAD83",
        DATUM["North_American_Datum_1983",
            SPHEROID["Geodetic Reference System of
1980",6378137,298.2572221008916,
                AUTHORITY["EPSG","7019"]],
            AUTHORITY["EPSG","6269"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4269"]],
    PROJECTION["Mercator_1SP"],
    PARAMETER["central_meridian",0],
    PARAMETER["scale_factor",1],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["METER",1]]

Esri WKT Description
PROJCS["Global_Mercator",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["Geodetic_Reference_System_of_1980",6378137,298.2572221008916]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Mercator"],PARAMETER["central_meridian",0],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1],PARAMETER["standard_parallel_1",0.0]]
</FME Parameters>

Intergraph's Geomedia Professional recognises the file as GeoTIFF, but
the chart appears to be in the same false place as with FME.

If you want, I could update the file's georeferencing by FME and
Geomedia so that location is correct. Then I could send listgeo
information or even put the actual files available if desired.

The goal is, of course, to get various software vendors to use the
GeoTIFF-information the same way. Hopefully the common way would also
be logically correct, but I guess that's too much to ask.

Best regards,

  Antti

Here is the listgeo info from the original file for those who are interested:

Geotiff_Information:
   Version: 1
   Key_Revision: 1.0
   Tagged_Information:
      ModelTiepointTag (2,3):
         0                0                0
         -9278434.53      4143530.21       0
      ModelPixelScaleTag (1,3):
         240.003787       240.003787       0
      End_Of_Tags.
   Keyed_Information:
      GTModelTypeGeoKey (Short,1): ModelTypeProjected
      GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
      GTCitationGeoKey (Ascii,16): "Global Mercator"
      GeographicTypeGeoKey (Short,1): GCS_NAD83
      GeogCitationGeoKey (Ascii,6): "NAD83"
      GeogAngularUnitsGeoKey (Short,1): Angular_Degree
      GeogSemiMajorAxisGeoKey (Double,1): 6378137
      GeogInvFlatteningGeoKey (Double,1): 298.257222
      Unknown-2062 (Double,3): 0                0                0
      ProjectedCSTypeGeoKey (Short,1): User-Defined
      ProjectionGeoKey (Short,1): User-Defined
      ProjCoordTransGeoKey (Short,1): CT_Mercator
      ProjLinearUnitsGeoKey (Short,1): Linear_Meter
      ProjStdParallel1GeoKey (Double,1): 47.667
      ProjNatOriginLongGeoKey (Double,1): 0
      ProjNatOriginLatGeoKey (Double,1): 0
      ProjFalseEastingGeoKey (Double,1): 0
      ProjFalseNorthingGeoKey (Double,1): 0
      ProjScaleAtNatOriginGeoKey (Double,1): 1
      End_Of_Keys.
   End_Of_Geotiff.
Projection Method: CT_Mercator
   ProjNatOriginLatGeoKey: 0.000000 (  0d 0' 0.00"N)
   ProjNatOriginLongGeoKey: 0.000000 (  0d 0' 0.00"E)
   ProjScaleAtNatOriginGeoKey: 1.000000
   ProjFalseEastingGeoKey: 0.000000 m
   ProjFalseNorthingGeoKey: 0.000000 m
GCS: 4269/NAD83
Datum: 6269/North American Datum 1983
Ellipsoid: 7019/GRS 1980 (6378137.00,6356752.31)
Prime Meridian: 8901/Greenwich (0.000000/  0d 0' 0.00"E)
Projection Linear Units: 9001/metre (1.000000m)
Corner Coordinates:
Upper Left    (-9278434.534, 4143530.209)
Lower Left    (-9278434.534, 3984167.694)
Upper Right   (-9165872.758, 4143530.209)
Lower Right   (-9165872.758, 3984167.694)
Center        (-9222153.646, 4063848.952)

2013/11/14 Trent Piepho <tpiepho at gmail.com>:
> It looks like arcgis does not support Mercator_1SP in geotiff files.
> It just ignores the scale factor and uses 1.0.  Which means in GDAL
> and libgeotiff as they are now, there is no way to export Mercator
> projections that don't have a scale of 1.0 to arcgis.
>
> ArcGIS does support Mercator_2SP, but instead of placing the latitude
> of true scale in ProjStdParallel1GeoKey, it uses
> ProjNatOriginLatGeoKey.  Which seems to be plainly wrong, yet that's
> what it does.
>
> I wonder if ESRI used libgeotiff?  With unpatched libgeotiff, the only
> way to get a latitude from a Mercator geotiff it to use one of the
> origin latitude GeoKeys.  It's not correct, but it does allow one to
> stick the number in the file and get it back out without having to
> modify or understand any libgeotiff code.
>
> It's possible that ArcGIS supports getting the latitude of true scale
> from ProjStdParallel1GeoKey, even it it doesn't store it there.
> Antii, could you test this file with ArcGIS?
>
> https://drive.google.com/file/d/0BybuTedE9CLxak9iakZRTC00cHM/edit?usp=sharing
>
> Pick file->download to get the geotiff file.
>
> It should have projection information like this:
>     PROJECTION["Mercator_2SP"],
>     PARAMETER["standard_parallel_1",47.667],
>     PARAMETER["central_meridian",0],
>     PARAMETER["false_easting",0],
>     PARAMETER["false_northing",0],
>     UNIT["metre",1,
>         AUTHORITY["EPSG","9001"]]]
> Origin = (-9278434.534151820465922,4143530.208984711207449)
> Pixel Size = (240.003786961970206,-240.003786961970206)
> Corner Coordinates:
> Upper Left  (-9278434.534, 4143530.209) (123d32'26.22"W, 48d23'56.59"N)
> Lower Left  (-9278434.534, 3984167.694) (123d32'26.22"W, 46d57'58.64"N)
> Upper Right (-9165872.758, 4143530.209) (122d 2'30.76"W, 48d23'56.59"N)
> Lower Right (-9165872.758, 3984167.694) (122d 2'30.76"W, 46d57'58.64"N)
> Center      (-9222153.646, 4063848.952) (122d47'28.49"W, 47d41'15.43"N)