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- Convert the surveyed coords to latitude, longitude and height. This system needs a reference ellipsoid such as the WGS84 system, and the height is assumed to be relative to the reference ellipsoid (it is hard to find definitive information on what the height actually means).
- Convert the lat, lon and height to the X,Y,Z absolute "Earth centred, Earth fixed" coordinate system where the origin is the centre of the earth. This conversion needs to assume the same ellipsoid as the conversion from UTM coords. The X axis points out of the equator at zero degs longitude, the Z axis points through the north pole along the rotation axis of the earth, and the Y axis completes a right-handed coordinate system. (Y points out of the equator in the Indian ocean at longitude 90 degs.) It is possible to specify the location of the telescope antennas in this X,Y,Z system in many software packages, but the numbers are very large and non-intuitive, so a local coordinate system is often preferred.
- Convert the X,Y,Z coordinates of the antennas to a local cartesian coordinate system where the origin of the system is the defined centre of the array. The axes of the local system are east (defined at the array centre), north (defined at the array centre) and height or "up". It is also worth noting that some software confusingly defines another "local X,Y,Z" system where the global X,Y,Z system has been rotated around the Z axis such that X points out of the equator at the meridian of the array centre. I'm not sure if there is an official name to this system, and it doesn't help much because the coordinates of the antennas are still large numbers and non-intuitive because the local horizon is angled to all coordinate axes.
- To convert to local E,N,U units, a rotation on the sphere is required. Note that rotations on sphere do not commute, and we need to do the longitude rotation before the latitude rotation.
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