[mapserver-users] Projection Issues

[Milo van der Linden]

The problem might be that in your mapserver proj4 implementation; the 
epsg:20355 is missing towgs84 parameters. These parameters tell 
mapserver the shift that is present between the wgs84 ellipsoid and the 
greenwich ellipsoid.

Could you check out the epsg file in your proj/nad directory; look up 
<20355> there and see if you have something like 
+towgs84=-70.9,-151.8,-41.4,0,0,0,0 default it says something like no_defs.
You can find a description on ellipsoid differences here:
http://www.remotesensing.org/proj/gen_parms.html

I looked up this somewhere on a mailinglist: ellps=aust_SA 
towgs84=-133,-48148,0,0,0,0

See if it can help you.

Good luck

Milo van der Linden



Gabe schreef:
> Hi
>
> I am having trouble with the projection on a raster image.  The map is being
> displayed but the raster layer is shifted by about 210m.
>
> The mapfiles main projection is EPSG:4326
>
> I have a .ecw file with this gdalinfo:
>
> Driver: ECW/ERMapper Compressed Wavelets
> Files: aerial_photo_2003.ecw
> Size is 53334, 53334
> Coordinate System is:
> PROJCS["TMAMG55",
>     GEOGCS["AUSTRALIAN GEODETIC",
>         DATUM["AGD84",
>             SPHEROID["ANS",6378160,298.25]],
>         PRIMEM["Greenwich",0],
>         UNIT["degree",0.0174532925199433]],
>     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["Meter",1]]
> Origin = (655179.380000000000000,7701896.290000000000000)
> Pixel Size = (1.500000000000000,-1.500000000000000)
> Corner Coordinates:
> Upper Left  (  655179.380, 7701896.290) (148d29'26.84"E, 20d46'34.32"S)
> Lower Left  (  655179.380, 7621895.290) (148d29'52.92"E, 21d29'55.68"S)
> Upper Right (  735180.380, 7701896.290) (149d15'32.31"E, 20d46'4.13"S)
> Lower Right (  735180.380, 7621895.290) (149d16'11.81"E, 21d29'24.34"S)
> Center      (  695179.880, 7661895.790) (148d52'45.97"E, 21d 8'1.22"S)
> Band 1 Block=53334x1 Type=Byte, ColorInterp=Red
>   Overviews: arbitrary
> Band 2 Block=53334x1 Type=Byte, ColorInterp=Green
>   Overviews: arbitrary
> Band 3 Block=53334x1 Type=Byte, ColorInterp=Blue
>   Overviews: arbitrary
>
>
> I have a vector layer which was a tab file with the projection AMG Zone
> 55(AGD 84).  This was loaded into postgis with ogr2ogr using these options
> ogr2ogr -overwrite -f "PostgreSQL" PG:"<database details>" thefile.tab -nln
> t_table -lco "GEOMETRY_NAME=the_geom" -t_srs EPSG:4326 -skipfailures.  I
> have done this before on different installations and it usually gives me a
> table where srid =4326 however in this case it is giving me a newly created
> srid = 32772 (this installation is different in that we are using postgres
> 8.3 and ms4w 2.2.7).  I have checked and as far as I can tell this layer is
> being displayed correctly.
>
> here are the relevant layers from my mapfile
>
> LAYER
>   NAME "Photography_2003"
>   GROUP "Photography_2003"
>   DATA "mackay/Images/aerial_photo_2003.ecw"
>   TYPE RASTER
>   STATUS ON
>   PROJECTION
>     "init=epsg:20355"
>   END
>   METADATA
>     "DESCRIPTION"    "Photography 2003"
>   END
> END
>
> And
>
>   LAYER
>     NAME "Paddocks"
>     GROUP "Paddocks"
>     STATUS ON
>     DATA "the_geom from t_the_table using unique oid using SRID=32772"
>     TYPE POLYGON
>     CONNECTIONTYPE postgis
>     CONNECTION "<connection string>"
>     MAXSCALE 2000000
>     CLASS
>       NAME "Paddock"
>       STYLE
>         ANGLE 120
>         WIDTH 1
>         SIZE 13
>         COLOR 0 128 0
>         OUTLINECOLOR 0 128 0
>         SYMBOL "hatched"
>       END
>     END
>   END
>
> Any help would be appreciated.
>
> Gabriel
>
>
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