How to stop raster layer being manipulated?

[Dave Pearson]

I have the Andes raster mapping for the UK in OSGB36 format. In addition, I 
have vector GPS information in lat/long decimal degree WGS84 format. 
Additionally, I have some extra data sets also in WGS84 format (mainly 
NAVTEQ). The mapserver is interfacing to another system through mapscript 
that requires to recieve and send lat/long co-ordinates in decimal degrees.

My problem is this: when I display the composite map, I get a vertical 
"squishing" of the raster layer as (presumably) gdal is translating the 
image on the fly into WGS84 space. OSGB36 is a pretty flat (and square!)  
projection, but I end up with a nicely curved and vertically foreshortened 
one with text that is then very difficult to read.
What I would ideally like is for mapserver to not attempt to manipulate the 
raster at all, but allow it to be projected effectively in OSGB dimensions 
but with lat / long units of measure instead of the OSGB units. This would 
ideally mean that my WGS84 data would reproject into effectively a "flat" 
space but still with lat /long units. Hope that makes sense, is it possible? 
Or is it something daft I'm doing with the PROJECTION that's causing all 
this fuss, I hope so! Can anybody offer me some guidance?

Here's my map def:

OUTPUTFORMAT
        NAME png
        DRIVER "GD/PNG"
        IMAGEMODE pc256
END
MAP
        STATUS ON
        SIZE 500 380
        EXTENT  -11.0 44.0 9.0 59.0
        UNITS dd
        SHAPEPATH "/var/gis/live"
        IMAGECOLOR 247 245 222
        FONTSET "/var/gis/live/fonts/fonts.txt"
        PROJECTION
                "proj=latlong"
                "ellps=WGS84"
                "datum=WGS84"
                "nodefs"
        END
LAYER
        NAME andesl7
        PROJECTION
                "proj=tmerc"
                "lat_0=49.000000000"
                "lon_0=-2.000000000"
                "k=0.9996012717"
                "x_0=400000.000"
                "y_0=-100000.000"
                "ellps=airy"
                "datum=OSGB36"
                "no_defs"
        END
        STATUS DEFAULT
         TILEINDEX "al7.shp"
        TILEITEM "location"
        TYPE RASTER
END
LAYER
        CONNECTIONTYPE postgis
        NAME custpoi_poly
        PROJECTION
                "proj=latlong"
                "ellps=WGS84"
                "datum=WGS84"
        END
        DATA "the_geom from custpoi_poly"
        CONNECTION "user=user password=password dbname=dbname 
host=127.0.0.1"
        STATUS DEFAULT
        TYPE POLYGON
        LABELITEM "description"
        CLASSITEM "symbol"
        TRANSPARENCY 30
        CLASS
                STYLE
                        COLOR 255 0 0
                END
                LABEL
                        ANTIALIAS TRUE
                        SIZE medium
                        COLOR 255 0 0
                        TYPE bitmap
                        FORCE TRUE
                        BACKGROUNDCOLOR 255 255 255
                        BACKGROUNDSHADOWCOLOR 255 0 0
                        POSITION AUTO
                END
        END
END

#
END # Map File


Many thanks in advance,

Dave Pearson

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