Documentation/example on how to use `thetaMode` geometry

[RemiLehe]

openPMD-api has great examples on how to write fields in Cartesian geometry.
Would it possible to add a small example for the thetaMode geometry?

[ax3l]

As it looks to me, thetaMode is already exposed in the geometry parameters.
It might not be functional/implemented yet, since thetaMode interferes with the number of elements we store/read. How do you currently represent such record components? As larger-element ND-arrays or do you add an additional dimension for the modes and imaginary parts?

[RemiLehe]

It is stored as an additional dimension, for the real/imaginary part of the modes, as described in the standard:
https://github.com/openPMD/openPMD-standard/blob/latest/STANDARD.md#required-attributes-for-each-mesh-record
Does this answer your question?

[ax3l]

Oh yes, 😆 I did read this section and skipped too fast about the detail that explains exactly this.

[RemiLehe]

No worries! If it helps you can of course also have a look at the thetaMode example datasets.

[RemiLehe]

@ax3l Since we are intensifying efforts to integrate openPMD-api into WarpX and (in the future) in openPMD-viewer, I think that this issue becomes quite key.
Any idea of who could be assigned to this issue, and what the timescale would be?

[ax3l]

Update: we are working on this since yesterday and it seams the only changes so far required in openPMD-api, besides adding good examples/docs, could be that

Mesh::setGridSpacing( ... );
Mesh::setGridGlobalOffset( ... );

should allow to omit the spacing in "rz-mode" index (so far we set 1.0 and 0.0 as dummies).

[ax3l]

Good news, the above mentioned functions do not check the dimensionality of meta-data, according to my test in #678... So maybe RZ works already (besides missing reconstruction helpers and docs) :-)