Auto Projections and WMS

[Steve Wormley]

I have managed to create an interesting problem.

I've created a shim CGI that accepts a WMS query in AUTO:42003 and uses the
Microsoft MapPoint SDK to return an image. This part works fine, if I call
mapserver with an SRS of AUTO:42003,9100,-121,38 and an appropriate
symmetrical BBOX with the same extents North and South(and east and west) it
calls my fake-WMS CGI with exactly those parameters and I return an image
apparently correct.

The problem comes in when I attempt to overlay my own(Postgis or even a
simple Grid) of unprojected(epsg:4326) data onto this layer.

It appears that during the translation the center of the bounding box is
shifted northwards, probably due to the curvature of the orthographic
projection. So the center of the image of the overlaid data is about 0.2
degrees more northern(38.2 in this example) So a point at -121,38 ends up
displayed 0.2degrees south of the same feature of the WMS layer.

So, I guess the question is: Should the center point provided in an AUTO
projection be the center point of the image assuming that the bounding box
is setup so 0,0 is the center of the bounding box?

I hope that makes sense.

Thanks,
-Steve Wormley