[FGS] gdal_translate projection query

[Eric Legge Smith]

Hello List

I have a 20000 x 20000 pixel geo tiff map in AGD66/AMG and I required a
1500 x 1500 pixel sub section of this map in WGS84/UTM Zone 55S in order
to directly plot GPS data.

To do the conversion, I used gdal_translate -srcwin Xoff Yoff Xsize Ysize
-a_srs "EPSG:32755" , however the coordinates of the projected map extents
(and the centre point) are approx 200m out  when compared to reference
points on the ground and consequently, the GPS data are also out by the
same 200m.

Am I doing something wrong in reprojecting from AGD66/AMG to WGS84/UTM
Zone 55S?

If so, how should I be reprojecting the original tif to bring it into
WGS84/UTM Zone 55S ?

Thank you
Eric Legge Smith
----------------------------------------

Gdalinfo reports the following:

Driver: GTiff/GeoTIFF
Size is 20000, 20000
Coordinate System is:
PROJCS["AGD66 / AMG zone 55",
    GEOGCS["AGD66",
        DATUM["Australian_Geodetic_Datum_1966",
            SPHEROID["Australian National
Spheroid",6378160,298.2500000000049,
                AUTHORITY["EPSG","7003"]],
            AUTHORITY["EPSG","6202"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4202"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",147],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",10000000],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AUTHORITY["EPSG","20255"]]
Origin = (316389.830000,5816178.022000)
Pixel Size = (0.34000000,-0.34000000)
Metadata:
  TIFFTAG_XRESOLUTION=0
  TIFFTAG_YRESOLUTION=0
  TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
Corner Coordinates:
Upper Left  (  316389.830, 5816178.022) (144d54'53.83"E, 37d46'59.49"S)
Lower Left  (  316389.830, 5809378.022) (144d54'47.62"E, 37d50'39.98"S)
Upper Right (  323189.830, 5816178.022) (144d59'31.66"E, 37d47'4.32"S)
Lower Right (  323189.830, 5809378.022) (144d59'25.68"E, 37d50'44.82"S)
Center      (  319789.830, 5812778.022) (144d57'9.70"E, 37d48'52.17"S)
Band 1 Block=20000x1 Type=Byte, ColorInterp=Red
  Overviews: 10000x10000, 5000x5000, 2500x2500, 1250x1250, 625x625,
313x313, 157x157
Band 2 Block=20000x1 Type=Byte, ColorInterp=Green
  Overviews: 10000x10000, 5000x5000, 2500x2500, 1250x1250, 625x625,
313x313, 157x157
Band 3 Block=20000x1 Type=Byte, ColorInterp=Blue
  Overviews: 10000x10000, 5000x5000, 2500x2500, 1250x1250, 625x625,
313x313, 157x157

Driver: GTiff/GeoTIFF
Size is 1500, 1500
Coordinate System is:
PROJCS["WGS 84 / UTM zone 55S",
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
            SPHEROID["WGS 84",6378137,298.2572235629972,
                AUTHORITY["EPSG","7030"]],
            AUTHORITY["EPSG","6326"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4326"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",147],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",10000000],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AUTHORITY["EPSG","32755"]]
Origin = (320130.471517,5814663.144103)
Pixel Size = (0.33999878,-0.33999878)
Corner Coordinates:
Upper Left  (  320130.472, 5814663.144) (144d57'25.26"E, 37d47'51.76"S)
Lower Left  (  320130.472, 5814153.146) (144d57'24.81"E, 37d48'8.30"S)
Upper Right (  320640.470, 5814663.144) (144d57'46.11"E, 37d47'52.12"S)
Lower Right (  320640.470, 5814153.146) (144d57'45.65"E, 37d48'8.66"S)
Center      (  320385.471, 5814408.145) (144d57'35.46"E, 37d48'0.21"S)
Band 1 Block=1500x5 Type=Byte, ColorInterp=Red
Band 2 Block=1500x5 Type=Byte, ColorInterp=Green
Band 3 Block=1500x5 Type=Byte, ColorInterp=Blue