[mapserver-users] Rotating a map

[Frank Warmerdam]

Tyler Mitchell wrote:

> Hi guys,  what would you do to rotate the orientation of your map?  Is
> using Proj realistic or not?
> I saw some emails back in July about this question - has anyone gone
> anywhere with this idea?


Tyler,

I have successfully used the resampling code in MapServer to do some
rotation of an ortho image.  In my particular test the georeferencing
information in a GeoTIFF file included rotational coefficients as shown
here:

warmerda at gdal[483]% listgeo small.tif
Geotiff_Information:
    Version: 1
    Key_Revision: 1.0
    Tagged_Information:
       ModelTransformationTag (4,4):
          0.999978707      -0.0065257527    0                467086.89
          -0.0065257527    -0.999978707     0                5365917.48
          0                0                0                0
          0                0                0                1
       End_Of_Tags.
    Keyed_Information:
       End_Of_Keys.
    End_Of_Geotiff.

As it happens GDAL will read these in and use these rotational coefficients
when going through the resampling process, so the image gets rotated back
to north-up.  You can accomplish the same thing by putting rotational
coefficients in a world file.  The above file would have a world file that
looks like this:

warmerda at gdal[487]% more small.tfw
             0.9999787070
            -0.0065257531
            -0.0065257527
            -0.9999787072
        467087.3871740954
       5365916.9739565337

Please feel free to contact me if you have problems settings this up and
doing it.  It is a rather esoteric use of the mapserver resampling logic.

PS. I have placed this text in the Wiki as:

   http://mapserver.gis.umn.edu/cgi-bin/wiki.pl?RotatingImages

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent