Cascading from the same server

[Howard Mark]

Arnulf,

Thanks for the info! I suspected as much. I have traced the problem to the image format. IF both the requesting (parent) URL  and the WMS (child) URL in the map file specify FORMAT=PNG, then everything works great. However I need a JPEG output - and that fails. 
The server WILL output JPEG - and a call to the child URL as JPEG works fine. It will just not work as a WMS layer. 
My server info is:
MapServer version 4.2.1 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP
SUPPORTS=PROJ SUPPORTS=FREETYPE SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT
INPUT=TIFF INPUT=EPPL7 INPUT=JPEG INPUT=SHAPEFILE


ANY IDEAS? Do I need other support? I have another server using 3.6 that cascades a WMS layer returning GIF and returns a JPEG. It uses GDAL. Could this be the problem?

Thanks,
Mark






Hi,
yes it can be done. You can define one MAP file as WMS and use it as a
datasource in another MAP file. It doesn't make a difference if it sits
on the same server (at least it works with us).

Some things should be noticed though:
If you need projections - cascaded layers are retrieved by MapServer in
the SRS defined in the layer section
LAYER
...
   PROJECTION
      "init=epsg:4326"
   END
...
and reprojected only afterwards to match the requested EPSG resulting in
poor quality (there is only a limited number of pixels for recalculating
the reprojected image). Lables an symbology gets warped because their
positions and sizes are not recalculated but just their pixels in an
images are stretched and rotated.
Performance gets worse for every cascaded WMS, as they are requested
sequentially. If one WMS does not answer the whole application / MAP
file is blocked.

Because of these reasons we tend to rather overlay WMS in a client.

Cheers, Arnulf.



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