Extents defined in mapfile versus those returned from GetCapabilities WMS request

[Geoff Dibley]

Hi there,

I have a mapfile that defines an extent and projection as follows;

EXTENT -2200000 -4700000 2000000 -1500000
PROJECTION
  "init=epsg:3112"
  # epsg:3112 (formerly 18001) is the same as the following:
  # "proj=lcc"
  # "ellps=WGS84"
  # "lat_1=-18d"
  # "lat_2=-36d"
  # "lat_0=0d"
  # "lon_0=134d"
  # "x_0=0d"
  # "y_0=0d"
END

Map Name, Projection, and required layer metadata (wms_title,
wms_onlineresource, and wms_srs) are all set as per the Mapserver WMS Server
How to.
Layer Name, Projection and metadata are set (wms_title) s per the Mapserver
WMS Server How to.

This all works OK - but I'm confused as to where the LatLonBoundingBox and
Bounding Box values in the GetCapabilities statement below are coming from;

<Layer queryable="1" opaque="0" cascaded="0">
        <Name>cities</Name>
        <Title>Cities and towns of Australia by type.</Title>
	  <SRS>EPSG:3112</SRS>
        <LatLonBoundingBox minx="-179.844" miny="-59.4692" maxx="179.937"
maxy="22.971" />
        <BoundingBox SRS="EPSG:3112"
                    minx="-1.03618e+07" miny="-6.85014e+06"
maxx="5.04576e+06" maxy="-8863.8" />

Are the bounding box x,y the actual extents (in epsg:3112 units) calculated
by Mapserver for that layer ?
How does this relate to the extents defined in the top level of the mapfile
(getmap requests on the layer limit themselves to these extents if no bbox is
specified) ?
Where do the latlonbounding box values come from - are they simply calculated
in Mapserver by converting the epsg:3112 co-ordinates tom lat/long ?

Any thoughts gratefully received !

Cheers,
Geoff