ISEA: inverse projection method is not implemented

[ppKrauss]

As expressed here, even with QGIS is impossible to "see ISEA". A projection is useless if we cannot visualize it... Without visualization you lose confidence and a multitude of applications.

At PROJ Readmes and/or documentation, ideal is to citate a "how to visualize" tutorial, or explain "Danger: you can calculate distances and areas, but can't visualize because there are implementation limitations".

[rouault]

even with QGIS is impossible to "see ISEA".

the reason is much likely that only the forward method (geographic coordinates -> projected coordinates) is implemented, whereas QGIS also requires the inverse method to be implemented. Which doesn't look (to me at least) as a trivial exercise

[rouault]

I see this was discussed in https://github.com/OSGeo/PROJ/issues/1778 already

[ppKrauss]

Hi @rouault, can you or other PROJ contributors reuse this CPP implementation of the inverse transform?

• https://github.com/riskaware-ltd/open-eaggr/blob/master/EAGGR/Src/Model/IProjection/Snyder.cpp#L190

• https://github.com/riskaware-ltd/open-eaggr/blob/master/EAGGR/Src/CoordinateConversion/CoordinateConverter.cpp

[rouault]

reuse this CPP implementation of the inverse transform?

no, it is licensed under LGPL v3 which is more restrictive than the MIT license used by PROJ. Someone could potentially extract the maths/algorithms to have a clean-room implementation, but we cannot directly derive code from that implementation

[ppKrauss]

Someone could potentially extract the maths/algorithms to have a clean-room implementation, (...)

Perfect!

[USGSExplorer1]

@rouault Professor, now I want to use ISEA to achieve the transformation between WGS84 and ISEA projection. But the problem is : no inverse transformtion. I can not acieve it .Can you tell me how to solve it ? Thank you!!

[busstoptaktik]

@USGSExplorer1, the PROJ Github repository is for discussing the PROJ source code, so do not post questions about PROJ usage here. You can seek advice for PROJ usage on the PROJ mailing list, cf. https://proj.org/community/channels.html

[USGSExplorer1]

@rouault

what is the meaning of this? Will the inverse transformation be implented?

[busstoptaktik]

@USGSExplorer1 If you provide a pull request with an implementation, I'm sure it will be seriously considered. PROJ is a contribution driven open source project - if you need a certain functionality, you're most welcome to provide it, or to hire someone capable to do it on your behalf.

So this is not the place to ask whether something will be implemented or not: It will, if someone makes it happen. That someone could be you, or anyone else having the need, willingness, and capability.