[mapserver-users] Zooming Strangeness

[Stephen Woodbridge]

I never saw any response to this post, I am somewhat at a loss on this.
Does anyone have any ideas. 

DM Solutions guys, 

Does the code in GMap that maps from pixel to map units work if I am
using lat/long data instead of meters like the original app was using?

Would it account for the symptoms I am seeing?

Any help would be appreaciated,
  -Steve W.

Stephen Woodbridge wrote:
> 
> 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