Using Craig Retro-azimuthal (Mecca) projection in QGIS?

Question

I'm using QGIS 3.4.12 and wanted to make a map with the Craig Retro-azimuthal projection.

The projection is not implemented in Proj4 and I couldn't find information about implementing new projections in the QGIS documentation. Is there anyway to "Install" the projection in QGIS?

score 2 · Accepted Answer · answered Apr 23 '20 at 09:16

QGIS uses the PROJ library for coordinate transformations and projections. Unfortunately, the Craig Retro-azimuthal projection is not implemented in the PROJ library.

Implementing it for use in QGIS requires adding the necessary code (written in C) to the PROJ library, compiling the PROJ library, and then compiling a new version of QGIS linked to the new version of the PROJ library. Here are examples of how other projections were added to the PROJ library: Tobler-Mercator projection, Equal Earth projection. Your best bet might be to open a feature request.

The Craig Retro-azimuthal projection is implemented in other programs:

D3 (with a fun interactive example)
Geocart

score 0 · Answer 2 · answered Apr 23 '20 at 04:18

0

You should first check the web site epsg.io to see if you can find the projection you want. If you can, it is a fair chance that QGIS can load it. If it is not a recognized projection, you can create a custom projection and save it for re-use but only if you know the parameters of the projection you require, or you can derive the parameters from known points. Look up Proj4 specifications on the web to see the sorts of information you need.

See (among others) this post: Defining new custom projections in QGIS?

And this post: Create custom projection using either QGIS or ArcGIS Desktop?

answered Apr 23 '20 at 04:18

Leigh Bettenay

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This answer doesn't help, because the Craig Retro-azimuthal projection is not implemented in Proj4 (which changesquare mentions in their question), so it can't be added to QGIS using the "Custom Projection" menu. – Jake Apr 23 '20 at 06:32
I believe it is not implemented. I'll update the question. – changesquare Apr 23 '20 at 08:19
@Jake - are there any guides on how to do that? – changesquare Apr 23 '20 at 08:23
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@Jake you should upgrade your comments to an answer. – Leigh Bettenay Apr 23 '20 at 08:43
@LeighBettenay: Done – Jake Apr 23 '20 at 09:17

Using Craig Retro-azimuthal (Mecca) projection in QGIS?

2 Answers2