[mapserver-users] Zooming Strangeness

[Stephen Woodbridge]

Hi all,

I am using a modified version of GMap75 which is working great, but I
have run into a strange problem related to zooming which may or may not
be related to the GMap code. I am using  

EXTENT -180.0 -90.0 180.0 90.0
UNITS DD

PROJECTION
  "proj=latlong" 
END

and all my data is in lat/long coordinates.

Here are two of the symptons:

1) I am zoom in to +-0.013 degrees (approx. 0.75 miles over 600 pix)
with a marker in the center of the image. I zoom out using rosa and the
GMap code and my marker is still at the same lat/long, the image zooms
out but has shifted so that the marker is now center on the lower left
quarter of the image like (M => marker position):

+--------------------+                 +--------------------+
+                    +                 +                    +
+                    +                 +                    +
+                    +                 +                    +
+                    +  < before       +                    +
+         M          +                 +                    +
+                    +                 +                    +
+                    +                 +                    +
+                    +    after >      +               M    +
+                    +                 +                    +
+--------------------+                 +--------------------+

If I recenter/pan (using rosa) and clicking on the marker it moves
correctly to the center.

2) I am zoomed to the full extents of the map and I try to zoom in on
roughly a 4 state area using rosa and the GMap code. I get the zoom but
the rectangle that is zoomed to is positioned significantly below the
rectangle I selected. For example, I zoom in on Massachussetts and I end
up somewhere in the Carribean. Likewise, is I try to pan to the correct
location using the reference map, I have to click up in Canada to end up
in Mass. I think there is also a horizontal shift like in 1) above so
these are both probably the same problem only magnified by scale.

Anyone have any ideas? I this an artifact that GMap75 was designed
around different assumptions regard the output projection?

You can try it out at

http://swoodbridge.com/cgi-bin/geo
http://swoodbridge.com/web2/nmap

I only have Tiger data loaded for the eastern half of the US.

Thanks for the help,
  Stephen Woodbridge