Image projection question

[Stephen Davies]

G'day.

I have a georeferenced TIFF aerial photo with the gdalinfo below.

Using a package called Farm Keeper, a shape file was created (by 
clicking on the image) containing several polygons defining paddocks. 
The shape file was then loaded into PostGIS using shp2pgsql and the 
results displayed with MapServer using the original geotiff as the 
raster layer.

The result was "almost right" except each of the polygons was displayed 
about 20m due north of it's correct position relative to the raster.

The polygon data is stored transformed to SRID 4283. The map projection 
is eqc with a central meridian of the centre of the polygons' MBR and 
the map extent is the MBR plus approx 100m - slightly smaller than the 
raster image extent.

Looking at the Map Server map coordinates, it appears that the polygons 
are correctly positioned (the mouse coordinates displayed match the 
originals) but the raster has been "moved" (stretched north/south).

Can anybody suggest what has happened?

Cheers and thanks,
Stephen Davies


Driver: GTiff/GeoTIFF
Size is 600, 448
Coordinate System is:
PROJCS["GDA94 / MGA zone 54",
    GEOGCS["GDA94",
        DATUM["Geocentric_Datum_of_Australia_1994",
            SPHEROID["GRS 1980",6378137,298.2572221010042,
                AUTHORITY["EPSG","7019"]],
            AUTHORITY["EPSG","6283"]],
        PRIMEM["Greenwich",0],
        UNIT["degree (supplier to define 
representation)",0.01745329251994328],
        AUTHORITY["EPSG","4283"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",141],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",10000000],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AUTHORITY["EPSG","28354"]]
Origin = (370139.138699,6182407.307100)
Pixel Size = (2.00000000,-2.00000000)
Metadata:
  AREA_OR_POINT=Area
  TIFFTAG_DOCUMENTNAME=ER Mapper 7.0
  TIFFTAG_IMAGEDESCRIPTION=ER Mapper GeoTiff raster translator V1.0: 
Band 1 = Red, Band 2 = Green, Band 3 = Blue
  TIFFTAG_SOFTWARE=ER Mapper 7.0
  TIFFTAG_XRESOLUTION=0
  TIFFTAG_YRESOLUTION=0
Corner Coordinates:
Upper Left  (  370139.139, 6182407.307) (139d35'8.28"E, 34d29'30.38"S)
Lower Left  (  370139.139, 6181511.307) (139d35'7.79"E, 34d29'59.46"S)
Upper Right (  371339.139, 6182407.307) (139d35'55.32"E, 34d29'30.92"S)
Lower Right (  371339.139, 6181511.307) (139d35'54.84"E, 34d30'0.00"S)
Center      (  370739.139, 6181959.307) (139d35'31.56"E, 34d29'45.19"S)
Band 1 Block=600x20 Type=Byte, ColorInterp=Red
Band 2 Block=600x20 Type=Byte, ColorInterp=Green
Band 3 Block=600x20 Type=Byte, ColorInterp=Blue

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