[mapserver-users] calculating min / max scaledenom based on projection

[Travis Kirstine]

Hi all,

We've been using mapserver as a WMS server and need to determine (outside
of mapserver) if a requested image contains layers defined in the getmap
request based on the layers min/maxscaledenom setting in the mapfile.  If a
request to the WMS is in the MAP SRS then we simply calculate the image
scale using a method like the one used in the mapscale.c msCalculateScale
and compare it to the MaxScaleDenom defined in the GetCapabilities and
everything works as expected.

The issue we have is that if the WMS GetMap SRS projection does not match
the native projection of the layer the maxscaledenom will vary.  For
example if the layers is in web mercator projection and has a maxscaledenom
of 25000 but the request is made in EPSG:4326 geographic the layer will not
be drawn above a scale of ~ 1:16000 in QGIS.

How can I calculate what 25000 equals for other SRSs?

How does mapserver calculate the min/max scaledenom for various projections
/ units?

Thanks
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