[PROJ] Finnish KKJ with triangle-wise affine transformation

[Oskari Timperi]

Hello,

In many places we still need to support the old KKJ (EPSG:2393) system. The National Land Survey of Finland (Maanmittauslaitos) provides a TIN network and affine transformation for each triangle for converting between ETRS-TM35FIN and KKJ. This is the preferred and most accurate way to convert to and from KKJ. More information and the plain text data files can be found from NLS website though only in Finnish but you should be able to get the idea https://www.maanmittauslaitos.fi/kartat-ja-paikkatieto/asiantuntevalle-kayttajalle/koordinaattimuunnokset

My question is, is this kind of transformation something that could be implemented inside PROJ at some point in the future? I don't know if this kind of thing is used anywhere else so it might be that this has very little use outside of Finland.

If this isn't viable, are there any plans about plugin support for PROJ? It would be cool to be able to implement custom steps and represent them as part of the normal PROJ pipeline to implement special needs :-)

Thanks!

Best regards,

-- 
Oskari Timperi
Software architect
Novatron Oy
https://novatron.fi/