[PROJ] Flaky tests for new tmerczoned projection

[Weston Renoud]

Hi all,

My PR to implement EPSG:32600 and EPSG:32700 got merged recently (https://github.com/OSGeo/PROJ/pull/4805), and I have noticed (as pointed out by Javier) this is causing intermittent/flaky test failures in the linux_gcc_32bit build. I've added an issue with the details https://github.com/OSGeo/PROJ/issues/4814. When the tests fail the projection is resulting in NaN values in the returned PJ_COORD for both forward and inverse.

Specifically, I'll looking for input on how I'm creating and using the Transverse Mercator projection in tmerczoned.cpp. The projection is using Transverse Mercator for the actual projection and then offsetting appropriately for the zone. So tmerc is being constructed in the initialization of tmerczoned, and I believe the initialization is incomplete (but sometimes right), and the source of the flaky failures.

I only saw an example of creating a "sub" projection in the in-review PR https://github.com/OSGeo/PROJ/pull/4770 and copied that. It relies heavily on pj_calc_ellipsoid_params, and manually copying forward the ctx and k0.

Is there a better approach to this initialization?

Any input greatly appreciated,
Weston Renoud


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