Jean-Sébastien Guay writes: > > > For example, from the specs document I've got, it seems the > coordinates > > we might get would look like > > > > 576120.324, 6224420.858, -102.73 > > I forgot to mention, what we have about the Z coordinate in > the spec is: > > "GPS-Z, positive going up towards the sky, which can be above > sea level, > zero is LAT (lowest astronomical tide), negative is going > down towards > the seabed, which could be subsea" > > How do I interpret that? What I want is a position to place > the object > in 3D space. I assume the seabed (terrain) will be positioned > correctly... And where do I put the ocean surface? Z=0 sounds like it > could be incorrect (by the presence of conditional verbs in > that sentence). > > Sounds like a very basic question, sorry about that.
Basic question yes Simple answer maybe It depends whether you want visualization or operational accuracy >From http://en.wikipedia.org/wiki/Geoid """Note that a GPS receiver on a ship may, during the course of a long voyage, indicate height variations, even though the ship will always be at sea level. This is because GPS satellites, orbiting about the center of gravity of the Earth, can only measure heights relative to a geocentric reference ellipsoid. To obtain one's geoidal height, a raw GPS reading must be corrected. Conversely, height determined by spirit leveling from a tidal measurement station, as in traditional land surveying, will always be geoidal height.""" See Google("GPS WGS-84") Google("WGS-84 ellipsoidal height") Here is a recent paper http://www.ngs.noaa.gov/PUBS_LIB/NGSRealTimeUserGuidelines.v2.0.2.pdf <shameless plug> ossimPlanet built on top of OSG uses a geoid corrected ellipsoid </> Norman _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
