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On 27/07/2013, at 1:10 AM, wrote:

> In C++ you can try the Proj4 library. It has a very complete set of projection transformation routines.  It’s used by many softwares and is open source.

On 27/07/2013, at 5:15 AM, Daniel Bolgheroni <> wrote:

> I've integrated Lua with GDAL for a project called nmodeller:
> Maybe you can take some ideas from it.

Thanks Carlos and Daniel for the references.  I'm not using raster data, and I have file readers for the formats I need, but thanks, I've had a look and will have a longer look later.  Proj4 is far more comprehensive than I need, and as I said, transliterating reference code to Lua wasn't that hard (though I "improved" a factorisation and confused myself for a while).  I prefer pure Lua where it doesn't require a ridiculous amount of reimplementation.

> If you where in Rio de Janeiro, for example , you would probably want to convert from Lat Long + WGS 84 to UTM (zone 23) + SAD69 (a stadard datum used in South america).

You actually use a different datum in South America?  We had what with the "old" NZMG, but the "new" NZTM is WGS84 UTM with a non-standard offset.  In any case, my requirement isn't to convert between interesting projections, but just to convert from Lat, Long to something roughly euclidean and back out again.