[mapguide-users] ScreenToMapUnits problems

[George McLean]

Hello,

I am experimenting with the ScreenToMapUnits(x,y) function in php with 
Apache on windows XP. I am capturing the screen coordinates of a mouse 
click with javascript and attempting to convert to map coordinates with 
ScreenToMapUnits. When I compare the results of ScreenToMapUnits with 
the coordinates in the status bar, the Y coordinate looks really 
accurate while the X coordinate is off. The amount X is off depends on 
the zoom level. The farther out I am zoomed the worse it is. My 
coordinate system is Wisconsin South State Plane Grid South NAD83 
(WI83-SF). At a zoom level where the map displayed is roughly 3 miles 
wide the error is about 2000'.

I am not sure if there is some problem in the capture of the screen 
coordinates or some other issue with the coordinate system. Has anyone 
seen this sort of problem or does anyone have any suggestions on how to 
troubleshoot this? How accurate should I expect ScreenToMapUnits to be?

Thanks

George McLean