[postgis-users] Image projection question

[Stephen Davies]

Driver: GTiff/GeoTIFF
G'day.

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

Using a package called Farm Keeper, a shape file was created containing 
several polygons defining paddocks. The shape file was then loaded into 
PostGIS using shp2pgsql and the results displayed with MapServer 
overlayed onto the original geotiff.

The result was "almost right" except each of the polygons was displayed 
about 20m 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 but the raster has been "moved".

Can anybody suggest where we have gone wrong?

Cheers and thanks,
Stephen Davies


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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