CRS of exported GeoJSON i CLI tool

[perliedman]

The coordinate transformation in the CLI utility is very much a hack as it is now, and only sort-of-works unless the map is located where I live :disappointed:

Mainly three possibilities:

1. let the exported GeoJSON be in whatever coordinate system it was drawn in - that is, don't try to reproject it to WGS84 latitude and longitudes. This leaves out the risk of converting incorrectly, but also has the downside that a lot of tools expect GeoJSON to be in WGS84 format (and the spec says it should be)
2. make the user specify the coordinate system on the command line, which will make the data correct, but the user might not know this
3. find out the correct coordinate system from the OCAD file: at least for some files, this is theoretically possible, although OCAD uses proprietary codes and not the official EPSG codes, so we would need to find the meaning of those codes

While I like 3, I have found no source for such a list, so I guess 2 is the best option, but the CLI tool should also probably support option 1 since it is sometimes desirable.

[jmacura]

Hi!

Ad 3) check out this repo: https://github.com/doppelmeter/OCAD-Grid-ID_to_EPSG It is also incorporated in @OpenOrienteering Mapper: https://github.com/OpenOrienteering/mapper/blob/master/src/fileformats/ocd_georef_fields.cpp

[perliedman]

Wow, that's fantastic! Thanks for the heads up, @jmacura !

[perliedman]

Since I rewrote the CLI tool it now uses option 2 above: exported CRS is the projection of the OCAD file. You can also extract the CRS name since ocad2geojson now knows about OCAD grid ids from the list linked above.

In the future, it should be possible to add an options to export:

• [ ] WGS84 GeoJSON, at least for the grids that map to an EPSG projection
• [ ] raw paper coordinates (OCAD units, 1/100 millimeter)