[postgis-users] asKML output and Google Earth projection

[Guido Lemoine]

Dear All,

I managed to integrate some asKML output (generated from an imported shape
file) with Google Earth and some georeferenced Very High Resolution (SPOT-5
and QuickBird) satellite GroundOverlays. We noticed location shifts between
(GPS-based) ground observations and the geocoded satellite imagery with 
respect
to the GE's (QuickBird like high res) background imagery of some 30-40 m.
Our imagery's geometry is geocoded to SPOT-5 georeferenced imagery,
which is tie-pointed to GCPs obtained with high quality GPS (which we 
consider
good quality).

I have been checking out GE projection information, and it says it is 
"Simple
Cylindrical (Plate Carree)" projection. I would expect this to 
correspond to
SRID = EPSG:4326 in postgis, although I would not call that a "Simple 
Cylindrical"
projection (rather something like "Simple Ellipsoidal"). Colleagues have 
told me
that the actual GE location error depends on location and has been 
improved a lot
with newly introduced imagery. A shift of 30-40 m is too much for VHR data,
though.

Any experience "out there" with this problem?

GL

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