[gdf] dimensionality doesn't imply which dimension is reduced

[Xarthisius]

Root cause that I was hitting this is that b"piernik" != "piernik"... However, I came to a conclusion that this clause is wrong for any GDF output, not just that one particular flavor. GDF already implies that RE/LE is a 3-element array, so there's no point in making assumptions about 1) which dimension is reduced or 2) what the value of dds in that dimension should be.

Using script from #3629:

import yt

ds = yt.load("crwind_tst_0001.h5")
slc = yt.SlicePlot(ds, "x", "density")
slc.save("zy.png")

ds.coordinates.x_axis["x"] = 2
ds.coordinates.x_axis[0] = 2
ds.coordinates.y_axis["x"] = 1
ds.coordinates.y_axis[0] = 1
slc = yt.SlicePlot(ds, "x", "density")
slc.save("yz.png")

now I get:

[neutrinoceros]

Well played !

Notes on the output graph:

• the axis labels are not changed
• the aspect of the figure varies widely, I suspect this is because the figure width is hardcoded (and the aspect ratio is always 1 by default)

These are points I'd like addressed along with the original issue you were pointing out: there's a demand for supporting this operation but the current solution is a little hacky as well as undocumented.

I'm writing this note on my phone mostly so I can open an issue from it later. I'm not asking for changes to the present PR.
I'll make an actual review in a couple hours.

[neutrinoceros]

So I did a little research on the data format and all I could find so far was a repo of yours
https://github.com/Xarthisius/fgdfio
which gives out a link to the format spec, which is unfortunately broken
https://bitbucket.org/yt_analysis/grid_data_format/

I confirm I can reproduce the error and that the patch fixes it, so I could just merge this, but out of curiosity, do you have any resource on this data format that I could refer to ?

[Xarthisius]

I confirm I can reproduce the error and that the patch fixes it, so I could just merge this, but out of curiosity, do you have any resource on this data format that I could refer to ?

https://github.com/yt-project/grid_data_format

[neutrinoceros]

@meeseeksdev backport to yt-4.0.x