[Chameleon] Problem with Scale widget

Paul Spencer pagameba at magma.ca
Wed Sep 22 12:51:46 EDT 2004


I'm not sure that the scale widget can zoom to an exact scale.  The 
scale is the relationship between units on the screen and units on the 
ground.  The scale calculations in mapserver take into account several 
factors, and the end result is an approximation of ground scale based on 
several assumptions concerning the dpi of the display and the distance 
of 1 degree at a given latitude (to name a couple).  So when zooming to 
a particular scale, this calculation is, in effect, reversed to 
determine how many ground units will fit inside a pixel and then the 
extents are set to match some approximation of this.

That being said, I don't think the discrepancy should be as big as you 
are indicating here so perhaps there is a problem.  Please file a bug 
about this and I will try to take a look at it.



Berend Veldkamp wrote:
> Hi,
> I have a problem with the scale-widget: When I enter a certain scale, 
> say 1:100000 and press enter, the map refreshes, but the value in the 
> edit box now shows 1:99872. Moreover, one of the layers that should show 
> at scale 1:100000 doesn't show consistently.
> If I type 1:99999 the scale becomes 1:99871
> Any ideas?
> Berend

|Paul Spencer                           pspencer at dmsolutions.ca   |
|Applications & Software Development                              |
|DM Solutions Group Inc                 http://www.dmsolutions.ca/|

More information about the Chameleon mailing list