[OSM-dev] map projection and scale distortion

David Earl david at frankieandshadow.com
Wed Apr 16 17:57:08 BST 2008


On 16/04/2008 17:44, Christopher Schmidt wrote:
> On Wed, Apr 16, 2008 at 05:26:16PM +0100, Tom Hughes wrote:
>>>  I flushed my browser cache. Still i cannot see any dynamic scale bar. Its
>>> static in the sense that the scale doesn't change with the latitude in
>>> focus.
>> Well I guess that's a bug in OpenLayers then ;-)
> 
> "Bug" is so harsh. "Lack of Feature" is so much nicer. :)
> 
> Seriously though, it's a difference in how you look at the problem. All
> of the code in projected maps anywhere assumes that within a plane,
> units are planar. This usually means that measuring large scale
> distances is not within the design. This is the case for the Scale
> control as well.
> 
> Implementing this as an option would not be difficult (Though it would
> require some discussion): Anyone interested is encouraged to talk to the
> OpenLayers Mailing List or IRC channel about it.

Seems to me like it is useful at and above some zoom level where 
horizontal and vertical are deemed near enough equal in the Mercator 
projection for the error to be insignificant.

BTW, I think the little bar is too short to be useful. It could do with 
extending some way across the bottom of the map, with divisions at the 
size it shows now. Ideally it wouldn't stray above the 'Permalink' link 
so that it doesn't reduce the area one can screenshot usefully at one 
time without edge decorations.

David




More information about the dev mailing list