Image projection saga (continued)

[Stephen Davies]

Despite feedback from this list, I have still not resolved my problem 
where data converted and transformed from a shape file to PostGIS does 
not project in the same way as the geotiff on which the shape file was 
based.

Previously, I was transforming the shape file coordinates from the 
original SRID 28354 to 4283 for storage in the database. When this data 
was overlaid on the raster image (SRID=28354), the polygons did not 
line up.

The map projection definition is:

    PROJECTION
        "proj=eqc"
        "ellps=GRS80"
        "towgs84=0,0,0"
        "no_defs"
       "lon_0=139.591e"
    END

I have now tried creating a polygon (SRID 28354) using the boundary 
coordinates of the raster image as determined from gdalinfo and 
overlaying that onto the image. (This removes the transform to 4283 and 
the subsequent reprojection to eqc.)

Still I see the polygon shift north by about 20m and by a tiny amount 
east.

This suggests to me that the method used to project geometries is 
somehow different from that used to project rasters as both sources now 
have the same SRID and could reasonably be expected to produce the same 
results.

To further confuse me, if I change the map projection to either 28354 or 
4283, everything lines up (but my scale bar and reference maps break).
I have searched all the documentation I can find but cannot find 
anything that describes the relationship between maps, sale bars and 
reference maps apart from a statement that reference map extent must be 
expressed in map units.

TIA,
Stephen Davies
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