ruwan
Posts: 1
Joined: Tue Nov 25, 2008 8:59 am

GpsTools to Google Earth cylindrical datum bug

Tue Dec 02, 2008 10:46 am

According to http://earth.google.com/userguide/v4/ug ... .html#note, Google Earth uses a cylindrical projection. There is an ESRI WKT for Google's projection here: http://spatialreference.org/ref/user/google-projection. However, I can't figure out how to specify a custom datum to support this projection in GpsTools. I tried:

CustomDatum toDatum = new CustomDatum();
//start Google Earth definition
toDatum.SemiMajorAxis = 6378137.0;
toDatum.E2 = 0.0; //IS THIS RIGHT???
toDatum.DeltaX = 0.0;
toDatum.DeltaY = 0.0;
toDatum.DeltaZ = 0.0;
toDatum.RotX = 0.0;
toDatum.RotY = 0.0;
toDatum.RotZ = 0.0;
toDatum.ScaleFactor = 0.0;

Position p = new Position();
p.Datum = Datum.WGS_84;
p.Longitude = 6.582388075; //from survey with 2 cm 1sigma
p.Latitude = 51.09916209; //from survey with 2 cm 1sigma
p.SetAltitude(95.8897487, 1);
p.CustomDatum = toDatum;

I expect a latitude on the order of 51.099149 in GEarth terms (the property line that I surveyed, rather than the middle of the house), but the results are 6.582388075, 50.9109526357591, -12812.7828332279 (almost a degree error in latitude and 10 km in altitude). Can you give me any hints?

Thanks,
Ruwan

User avatar
johan
GpsGate
Posts: 15353
Joined: Wed Aug 04, 2004 10:40 pm
Location: Sweden
Contact: Website

RE: GpsTools to Google Earth cylindrical datum bug

Tue Dec 02, 2008 1:10 pm

Google uses WGS84.

Regards,
Johan

Franson Support

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