How to define projections in GIS Software

[Hai-Etlik]

Finding this article was a real relief. I was starting to think I was the only person interested in making up projections.

How would I go a stage further and define my own projection for the map? By that I mean not a tweak to Winkle Tripel, Gnomonic nor Peirce Quincuncial, but an equation that I type in to define the form that the map takes?

That requires writing an implementation and including it in Proj4. For instance, this is what the implementation of Lambert Conformal Conic looks like https://github.com/OSGeo/proj.4/blob...r/src/PJ_lcc.c

[mapomatic]

That requires writing an implementation and including it in Proj4.

Oh. Thanks for the quick reply. Proj4 does sound good, but is there any solution that doesn't require re-compiling a computer program every time I change something, such as a program that can open a definitions file and apply it? I see that Proj4 can use .prj definition files which is a step in the right direction, but it seems that these cannot define the fundamental projection mathematics.

Thank you

[Hai-Etlik]

Oh. Thanks for the quick reply. Proj4 does sound good, but is there any solution that doesn't require re-compiling a computer program every time I change something, such as a program that can open a definitions file and apply it? I see that Proj4 can use .prj definition files which is a step in the right direction, but it seems that these cannot define the fundamental projection mathematics.

Thank you

I'm not aware of any GIS software that has an integrated CAS type functionality to define projections. I expect such an on the fly custom projection definition would be significantly slower. As it is, defining even a coordinate system based on existing projections is a fairly unusual thing in GIS. That's why it tends to involve writing a Proj4 config string or WKT by hand rather than a discoverable UI with dynamic projection view with Tissots indicatrix or a distortion colour map.