[mapserver-users] WCS reprojection issue

[Mark Phillips]

Hi,

I'm struggling with an issue related to projections in a MapServer WCS
service.  I've got a raster data file that is in EPSG:2163, and I'd like to
serve it via WCS in EPSG:4326.  The only way I have managed to get this to
work is to reproject the data manually in advance and then reference the
ESPG:4326 copy of the data in my mapfile.  When I do that, with the mapfile
below, the service seems to work beautifully. What I really want, though, is
to be able to leave my data in its original projection and have MapServer
reproject on the fly.

When I change the mapfile to use the original ESPG:2163 copy of the data,
and update the relevant projections in the mapfile from 4326 to 2163,
though, the service breaks, in the sense that the data shows up in (very
much) the wrong place.  I first tried just changing the
projections commented in the mapfile below with ###LAYER_PROJECTION and
###LAYER_WCS_SRS from 4326 to 2163 (after changing the DATA line in the
layer to point to the EPSG:2163 copy of the data, of course), but that
didn't work.  I then experimented with changing the ###SERVICE_WCS_SRS line
and/or the ###MAP_PROJECTION as well, but no luck.

What is especially confusing is that I *can* get this to work for a WMS
service.  In the case of WMS, MapServer seems quite happy to serve EPSG:2163
data in ESPG:4326, as long as the ###LAYER_PROJECTION and ###LAYER_WCS_SRS
lines say EPSG:2163 (with "wcs" replaced by "wms", of course).

I'm sure that part of my problem is that I don't completely understand the
purpose served by each of the various projections specified in the mapfile.
 Can someone offer some insight into what the correct approach is to getting
MapServer to reproject on the fly in a WCS?

In case it matters: I'm using MapServer 6.0, and am testing the WCS with
ArcMap 9.3.

Thanks!

--Mark

Here is my working mapfile for ESPG:4326:

    MAP
      NAME       lucky
      STATUS     ON
      SIZE       600 400
      EXTENT     -83.938  34.746  -81.340  36.361
      IMAGECOLOR 255 255 255

      WEB
        METADATA
          "ows_enable_request"     "*"
          "wcs_label"              "My WCS Service"
          "wcs_srs"                "EPSG:4326"   ###SERVICE_WCS_SRS
        END
      END

      PROJECTION
       "init=epsg:4326"  ###MAP_PROJECTION
      END

      LAYER
NAME     mylayer
        TYPE     RASTER
DUMP     TRUE
        STATUS   OFF
DATA     sampledata_wgs84/tif_wgs84.tif
        INCLUDE  "colormap.cmap"
        PROJECTION
          "init=epsg:4326"   ###LAYER_PROJECTION
        END
        METADATA
          "wcs_srs"                    "EPSG:4326"  ###LAYER_WCS_SRS
          "wcs_label"                  "My Layer"
          "wcs_rangeset_name"          "My Range"
          "wcs_rangeset_label"         "My Label"
        END
      END
    END
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