[Geowanking] [georss] [Geojson] simple 3D geocode for AR

Dan Lyke danlyke at flutterby.com
Tue Sep 1 14:01:23 PDT 2009


On Tue, 01 Sep 2009 20:20:41 +0200
Christian Willmes <c.willmes at uni-koeln.de> wrote:
> Maybe I don't understand what you talking about the necessity to use 
> local coordinate systems, so can one please clarify to me, why one
> can't (or should not) model - as precisely as you just want - every
> single (not moving) point on earth in a Geocentric Spatial Reference
> Frame [1]?

I'm not following this thread as closely as I should be, but another
good reason to use local coordinate systems is that sometimes you know
where points are relative to some local reference, but you don't know
where that reference is very precisely in global terms.

For instance, take a picture of something, there may be ways that you
can pull information out of that picture with millimeter precision, but
if you used a consumer GPS device to log where that picture was taken
from, then the accuracy you get is good to ten meters or so.

Dan





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