GeoCoordinate: minor improvements to UTMtoGC
GeoCoordinate: added GCtoUTM
GeoCoordinate: minor improvements to GDtoGC
GeoCoordinate: minor improvements to GCtoGD
GeoCoordinate: added GCtoGEO
GeoCoordinate: added GCtoX3D
GeoCoordinate: use GCtoX3D for GEOtoX3D