[gdal-dev] geotiff false easting/northing unit nuisance

[Andrea Battisti]

Hello,


I am trying to have GDAL play nice with some geotiff aerial images, and 
I have an issue with the way the units are handled on the false 
easting/northing parameters.

The images use the California State Plane projection (zone 2), in feet, 
not meters, i.e.:
http://spatialreference.org/ref/epsg/2226/



Now, this is what I get from listgeo:

Geotiff_Information:
    Version: 1
    Key_Revision: 1.0
    Tagged_Information:
       ModelTiepointTag (2,3):
          0                 0                 0
          6391500           1996000           0
       ModelPixelScaleTag (1,3):
          1                 1                 0
       End_Of_Tags.
    Keyed_Information:
       GTModelTypeGeoKey (Short,1): ModelTypeProjected
       GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
       GTCitationGeoKey (Ascii,318): "...
Projection Name = NAD_1983_StatePlane_California_II_FIPS_0402_Feet
Units = us_survey_feet
GeoTIFF Units = us_survey_feet"
       ProjectedCSTypeGeoKey (Short,1): PCS_NAD83_California_2
       PCSCitationGeoKey (Ascii,228): "...
State Plane Zone -402
NAD = 83"
       ProjLinearUnitsGeoKey (Short,1): Linear_Foot_US_Survey
       End_Of_Keys.
    End_Of_Geotiff.

PCS = 26942 (name unknown)
Projection = 10432 ()
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: 9003/US survey foot (0.304801m)

Corner Coordinates:
Upper Left    ( 6391500.000, 1996000.000)
Lower Left    ( 6391500.000, 1991000.000)
Upper Right   ( 6396500.000, 1996000.000)
Lower Right   ( 6396500.000, 1991000.000)
Center        ( 6394000.000, 1993500.000)




And this is what I get from gdalsrsinfo (I tried both GDAL 1.9.2 and 
1.10.1, same result):


PROJ.4 : '+proj=lcc +lat_1=39.83333333333334 +lat_2=38.33333333333334 
+lat_0=37.
66666666666666 +lon_0=-122 +x_0=6561666.666666666 +y_0=1640416.666666667 
+datum=
NAD83 +units=us-ft +no_defs '

OGC WKT :
PROJCS["NAD_1983_StatePlane_California_II_FIPS_0402_Feet",
     GEOGCS["NAD83",
         DATUM["North_American_Datum_1983",
             SPHEROID["GRS 1980",6378137,298.2572221010002,
                 AUTHORITY["EPSG","7019"]],
             AUTHORITY["EPSG","6269"]],
         PRIMEM["Greenwich",0],
         UNIT["degree",0.0174532925199433],
         AUTHORITY["EPSG","4269"]],
     PROJECTION["Lambert_Conformal_Conic_2SP"],
     PARAMETER["standard_parallel_1",39.83333333333334],
     PARAMETER["standard_parallel_2",38.33333333333334],
     PARAMETER["latitude_of_origin",37.66666666666666],
     PARAMETER["central_meridian",-122],
     PARAMETER["false_easting",21527734.72222222],
     PARAMETER["false_northing",5381933.680555555],
     UNIT["us_survey_feet",0.3048006096012192],
     AUTHORITY["EPSG","26942"]]


That is very close to what I expect, except for the false 
easting/northing and thus x_0/y_0, which should be:

     PARAMETER["false_easting",6561666.667],
     PARAMETER["false_northing",1640416.667],

and in meters:+x_0=2000000 +y_0=500000


Now, I understand that this is an "obscure" area and it has already been 
discussed in the past, e.g.:
https://trac.osgeo.org/gdal/ticket/3901
https://trac.osgeo.org/gdal/ticket/4954
but it is not clear to me if there is something weird on these specific 
geotiff files, or on the GDAL side, or a combination of both
(by the way, these files work fine on ESRI software).

In this case, looks like that the WKT/Proj is read from external 
projection definition files, is it possible the force GDAL to show the 
right parameters without trying to adjust the units?



Thanks in advance and sorry for the long post!
Andrea Battisti, IT Engineer