[Chameleon] Problem with Scale widget

Berend Veldkamp berend.veldkamp at aris.nl
Thu Sep 23 03:51:53 EDT 2004


Apparently it depends on the values I use for the width and height of 
the MapWidget: with 780x537 the scale widget displays a value other than 
I typed, a change of one pixel in either width or height solves it.

BTW I'm not really concerned about the actual scale on screen, as long 
as the value I type in the scale editbox remains the same and scale 
dependent layers become visible at the right scale.


Paul Spencer wrote:
> Berend,
> 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.
> Cheers,
> PAul


Berend Veldkamp - ARIS

More information about the Chameleon mailing list