John Caron writes:
# Can one figure out all the possible parameter values from the
# WMT_MS_Capabilities document?
Yes. Some of them are explicitly enumerated (such as available formats
and map projections), while others are numeric (bounding box) and
therefore not explicitly specified. There is a mechanism for
vendor-specific parameters but they are little used and clients are
free to completely ignore them.
# Does the WMS spec allow the client to specify the projection ?
The client may choose any of the projections ("Spatial Reference
Systems" or SRS) that the server lists in its Capabilities XML.
# In the specific example above of the topo map, can the client
# specify/discover what the false color mapping is?
An optional LegendURL element can let a human see what the mapping is.
A WMS that offers the optional "Styled Layer Descriptor" functionality
(the subject of a 2nd spec) does let the user make choices about the
representation, especially for vector data (points, lines, polygons).
In the last OGC testbed we just began experimenting with ways to
specify the portrayal of coverages (e.g., gridded data). The testbed
starting next week will hopefully make further progress in that area.