gps and gpsAltitude were added in SDKv4, dunno whether that will suffice.
to see all items, do
Debug.lognpp( photo:getRawMetadata( nil ) )
using John Ellis' Debug Toolkit.
PS - if the info you need is not available via SDK, you have to do LrTasks.execute( exif tool.. ), or something similar.
Thanks, Rob. Unfortunately these two fields are not sufficient. There is another EXIF field Exif.GPSInfo.GPSImgDirection that contains the direction of the photographer in degrees.