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I am experiencing some unexpected results when trying to use MapServer to create images with a polar projection. I am using the standard BlueMarble tif as the base layer (in wgs84 GCS) and am trying to reproject image into WGS 84 / UPS North (WKID 32661). The polar region seems to be getting 'clipped' out of the image.

The attached image was created using the mapfile below along with the shp2img utility included with ms4w.

Can anyone explain whats going on here?

--Mapfile MAP

NAME BMNG
STATUS ON
SIZE 800 500
IMAGETYPE PNG
UNITS METERS
EXTENT -28567783.609 -28567757.697 32567757.697 32567783.609
IMAGECOLOR 255 255 255
CONFIG "PROJ_LIB" "C:/DevTools/ms4w/proj/nad"
PROJECTION
    "proj=stere"
    "lat_0=90"
    "lat_ts=90"
    "lon_0=0"
    "k=0.994"
    "x_0=2000000"
    "y_0=2000000"
    "ellps=WGS84"
    "datum=WGS84"
    "units=m"
    "no_defs"
END

LAYER
    NAME 'BMNG_UPSN'
    TYPE RASTER
    STATUS DEFAULT
    DATA 'D:\stuff\bmng\bluemarble.tif'
    PROJECTION
        "init=epsg:4326"
    END
END #LAYER

END #MAP

enter image description here

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1 Answer

This isn't completely a MapServer issue it's an issue with the standard BlueMarble tif. It's just not intended to be displayed as a Polar projection.

As you zoom into the hole you should see some content, but there will always be a hole.

You can see the same effect in the below image showing Antarctica, in this instance we have the standard BlueMarble image (and hole) and another image (LIMA) intended to be shown in the polar region. Both are being served from the same MapServer instance.

LIMA vs BlueMarble

You will have a better experience if you clip the BlueMarble tiff, removing say everything South of 60 degrees North, such as in this (below) instance; but note you will (probably) still get some artefacts at various zoom levels. In essence the smaller (geographically) your image, the better your resultant image will be.

Top 60 degrees of BlueMarble

That said however there is an outstanding bug with MapServer polar reprojection bug revisited which means that some polar projections don't work as well as others...

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