[josm-dev] Geometric calculations and projections
tobias.wendorff at uni-dortmund.de
Thu Dec 17 15:30:55 GMT 2009
Matthias Julius schrieb:
> This is actually a good example why we might want to use Mercator for
> calculating rectangles.
Which Mercator are you talking about?
- Spehrical Mercator / Web Mercator (it's using a sphere)
- "real" Mercator (Earth is flattened)
- Transverse Mercator (on sphere or ellipsoid?)
- Universal Transverse Mercator (on sphere or ellipsoid?)
If you want to use the "normal" Web Mercator, OSM and Google use,
it would be better to use spherical geometry ... it's more accurate
than calculation into a projection and back to LatLon.
Spherical geometry allows you to calculate _directly_ on the sphere
without using a projection ... you simple use LatLon in radian
I can do some calculations about accurancy the next week, perhaps
sphere is enough ... but as soon as you work on big objects, you
might run into problems.
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