I'm using GDAL to convert coordinates from one system (geographic or projected) to another.
Assume I want to convert geographic coordinates (latitude and longitude) in the WGS84 datum, to UTM coordinates in the Amersfoort datum (EPSG:4289).
In order for GDAL to determine the UTM coordinates (easting and northing), it needs:
- the input spatial reference system: geographic, based on the WGS84 datum
- the input coordinates: latitude and longitude
- the target spatial reference system: projected - UTM -, based on the local Amersfoort datum
To instantiate the target SRS, besides the datum, I need to specify the zone and the hemisphere.
The question is: How to I determine the UTM zone and hemisphere where the input geographic coordinates fall in? I could use the Wikipedia article for that. As far as I understood, the mechanism described there works for determining the zone and hemisphere for geographic coordinates in the WGS84 datum. What is not clear to me is whether the resulting zone and hemisphere make sense only for the WGS84 datum, or if they can be used in any, local or global, datum.
If the zone and hemisphere determined from geographic coordinates in the WGS84 datum only make sense for determining the UTM coordinates in that same WGS84 datum, how can I determine the UTM zone and hemisphere in another datum - WGS72, NAD27, NAD83 etc.?
Also, does it even make sense to speak of UTM coordinates in a local datum?
I hope I haven't messed up the concepts too much. Anyway, any pointers will be greatly appreciated.