# projection for high accuracy small areas

I need to convert (lat,long,height)points into a cartesian system for an area as small as 40kmx40km or even 10kmx10km. I'm currently using the UTM projection, but there are some issues regarding accuracy and distortion. The good thing with UTM is that GDAL library easily do the math via python coding.

My professor told me 'plano topográfico local' (in Portuguese) would be a good option. The bad thing is that I have no idea of the EPSG code for this system in order to use GDAL. Any ideas?

• I'm guessing that 'plano topográfico local' will translate to 'local coordinate system' which I think means that you will not find an EPSG code for it because it may have been created as a "one-off".
– PolyGeo
Commented Jun 12, 2015 at 3:18
• It depends what you're trying to do with the data in the 'Cartesian' coordinate system. Different projections have merits and detriments.. so UTM doesn't work - why? what's wrong with it? How can you tell it's not accurate? According to the Heisenberg's uncertainty principle everything is inaccurate. Commented Jun 12, 2015 at 3:37
• Although you write about "some issues," exactly what are they? What forms of distortion are of concern? What are your actual accuracy requirements? Depending on what they might be, you might find UTM acceptable, or you could apply a very simple adjustment (change the scale factor), or you might need a more customized projection. Commented Jun 12, 2015 at 16:44
• Thanks @PolyGeo. I guess I will have to create my own projection. In order to do that automatically, I'm possibly implementing some python code. Commented Jun 15, 2015 at 12:40
• @MichaelMiles-Stimson, thank you for the comment. I have searched for literature comparing the amount of distortion provided by different projections, but never found it. I was working with UTM when I found a brazilian standard NBR 14166:1998 that sets "plano topográfico local" as the system to used in areas as small as 50km x 50km. That system ignores earth curvature, but considers terrain heights. On the other hand, as I understood, UTM considers the ellipsoid , but tackles altitude as and attribute. Commented Jun 15, 2015 at 12:54