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I'm working in a project that have no documentation and I'm trying to figure out which coordinate system is being used in their API. What I know is that they have a coordinate like this:

latitude: -12168371
longitude: -27370165

And this maps to somewhere near this coordinate in the EPSG:4326 system:

latitude:-20.274378
longitude:-45.62233

Is there any service/clue/process that could help me find which coordinate system is being used?

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    Do the points appear to be over the whole globe or are all the points in a small area of lat-long? What's the numeric range of the coordinates - could it be metres, centimetres, miles, feet? I couldn't get any joy out of projfinder either but sometimes scaling the units knowing its miles and proj uses km helps. More detective work needed! – Spacedman Jan 5 at 15:34
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    Looks like the lat / lon were multiplied by 600,000. If I divide your numbers by 600,000, I arrive at -20.2806183, -45.6169416, near the point you mention in Calcario Cazanga mining site in Arcos, Brazil. If you apply this logic to all your coordinates (divide them by 600,000), and then assign epsg 4326, does it work? – FSimardGIS Jan 5 at 22:20
  • @FSimardGIS How did you get to this idea of dividing by 600,000? – TomazicM Jan 6 at 18:05
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    @TomazicM I've seen cases where latitudes and longitudes were expressed in milliarcseconds, arcminutes, etc, so I figured I could check this out by dividing both coordinate pairs and see if the result matched a nice round number beginning in 60 or 3600. In this case, it looks like the units might be derived from arcminutes, something like this: Latitude = -20°16.8371' > -1216.8371' > -12168371 – FSimardGIS Jan 6 at 20:11
  • I think it would be very useful if you publish this as an answer. – TomazicM Jan 6 at 20:28
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It looks like those latitudes and longitudes are based on arcminutes somehow. If I divide your numbers by 600,000, I arrive at -20.2806183, -45.6169416, close to the point you mention in Calcario Cazanga mining site in Arcos, Brazil:

enter image description here

If you apply this logic to all your coordinates (divide them by 600,000), and then assign epsg 4326, that might be the conversion you're looking for.

I've seen cases where latitudes and longitudes were expressed in milliarcseconds, arcminutes, etc, so I figured I could check this out by dividing both latitudes and both longitudes and see if the result closely matched a nice round number beginning in 60 or 3600. In this case, it looks like the units were derived from arcminutes, maybe with a logic like this:

  • Latitude = -20°16.8371' > -1216.8371' > -12168371
  • Longitude = -45°37.0165' > -2737.0165' > -27370165
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