Datum Shift

Discussion created by helyxsisltd on May 3, 2013
If I were to place a GPSLayer on top of a map that is projected in British National Grid, then I would need to address the issue that the GPS data (in WGS84) was using a different spatial reference from the map.

Looking at the GPSLayer Members, I can set a ProjectionService (e.g. to a local geometry service) in order to perform a behind-the-scenes projection.

My question is - will the ProjectionService also choose an appropriate GeoTransformation to apply (to transform from the WGS84 datum to the OSGB36 datum that underlies British National Grid)?

If it does, then how do I ascertain which transformation it is using? And if it doesn't, then I can expect to witness a datum shift, whereby the GPS will display in the wrong location - what can I do about this, short of writing my own GpsLayer?