Hi,
One can convert {lat, lon} coordinates from one datum to another (say WGS84) with GeoPosition, but we need to know the original datum as well. Do you know what's the original datum? For example this is a change from WGS72 to WGS84 (in its original form, because there are several versions):
In[20]:= GeoPosition[GeoPosition[{49.74645, 8.54444}, "WGS72"], "WGS84Original"]
Out[20]= GeoPosition[{49.7465, 8.54459}, "WGS84Original"]
Or do you want, perhaps, to convert {lat, lon} coordinates to a triple {x, y, z} in an Earth-Centered frame? That would be done with GeoPositionXYZ:
In[21]:= GeoPositionXYZ[GeoPosition[{49.74645, 8.54444}, "WGS72"], "WGS84Original"]
Out[21]= GeoPositionXYZ[{4.08359*10^6, 613547., 4.84462*10^6}, "WGS84Original"]
Jose.