[OSM-dev] map projection and scale distortion

Tom Hughes tom at compton.nu
Wed Apr 16 17:34:22 BST 2008


In message <54445.83.43.179.8.1208363147.squirrel at webmail.escomposlinux.org>
          Iván Sánchez Ortega <ivansanchez at escomposlinux.org> wrote:

> <quote who="Raghu Ram">
> >
> >  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.
> 
> Yes, the projection (EPSG:900913) is the same spherical mercator as
> google's. Yes, the slippy map scale should change with the latitude in
> focus.

Well that rather depends really - the amount the scale changes by
depends what direction you are measuring in. Along a line of longitude
it doesn't change at all. Along a line of latitude is does, and in
between it changes rather less.

At least I think that's right...

> However, keep in mind that OpenLayers 2.6 was released, and deployed into
> OSM's slippy map just today - give it a couple o' days, and the scale bar
> will change depending on the latitude.

I doubt that because (a) somebody would have to write code to make
it dynamic and (b) somebody would have to convince me to patch our
copy of OL instead of waiting for the next release ;-)

Tom

-- 
Tom Hughes (tom at compton.nu)
http://www.compton.nu/




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