[ gpsdrive-Bugs-2203405 ] OSM download maps incorrectly scaled

[<gps...@li...>]

Bugs item #2203405, was opened at 2008-10-28 21:34
Message generated for change (Comment added) made by hbowman
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Category: Map Download
Group: gpsdrive-svn
Status: Open
Resolution: None
Priority: 6
Private: No
Submitted By: Hamish B (hbowman)
Assigned to: Nobody/Anonymous (nobody)
Summary: OSM download maps incorrectly scaled

Initial Comment:
Hi,


the OSM download maps are incorrectly scaled. It is only slightly wrong, but noticeable.

if someone can dig out the code their download site uses to determine the scale level, I can redo the GpsDrive side of things so that it matches and scales perfectly.

I'd also note that using their current projection anything over 1:500,000 will have too much distortion to be very useful. Try downloading a world wide OSM map using the Options->Maps->Download tool and then in Pos. Mode slowly click your way to +-90 deg lon from the center. you will see the cursor jump to the pole..

for those scales plate caree (top_* maps) are appropriate, for the Landsat maps I've made it do the transition as we can tell the WMS server what we want, but for the OSM map download I fear we have no choice besides allow download of crap maps or stop offering to download more than 1:500k.


thanks,
Hamish


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>Comment By: Hamish B (hbowman)
Date: 2008-12-17 02:31

Message:
This is fundamentally a projection bug in Osmarender:
  http://wiki.openstreetmap.org/wiki/Osmarender_bug

Osmarederer following Google's lead of using Merc proj on a sphere is a
major PITA for any mapping applications where geolocation counts. Read
ongoing thread/rants about the "Google Sphere" on the PROJ4 mailing list:
http://news.gmane.org/gmane.comp.gis.proj-4.devel/


best would be if OSM put together a WMS server, then we could reuse the
working-well WMS code which NASA LANDSAT maps are using.


Hamish


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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=770280&aid=2203405&group_id=148048