Problem downloading grids on the fly

[j-carson]

The following code used to work with pyproj==3.6.1

    WGS84 = "EPSG:4979"  # https://epsg.io/4979
    EGM96 = "EPSG:9707"  # https://epsg.io/9707

    tg = TransformerGroup(WGS84, EGM96)
    if tg.unavailable_operations:
        tg.download_grids(verbose=True)

    transformer = Transformer.from_crs(CRS(EGM96), CRS(WGS84), always_xy=True)

But with pyproj==3.7 I'm getting a no-op transform - the grid I tried to download isn't actually being used.

This bug only manifested itself in my CI system, which starts with a completely clean environment. If I look in the .local/share/proj directory in the build system, I see that the grid is there us_nga_egm96_15.tif, but if I look in my "messy" system where it wasn't failing, I have files.geojson in there as well.

I found the call to get_transform_grid_list() which puts the missing files.geojson there.

With that call added, the test still fails the first time I run it, but once both files are in place, the second time you run the program, the tests succeed.

How can I reliably download grids on the fly?

[snowman2]

Related: #705

[j-carson]

@snowman2 Could you explain why this is related? I don't think there is a network error as the grid is successfully downloaded, just not used.

Edit to add: This is also an older issue, and the regression in behavior happened between pyproj 3.6.1 and 3.7.0.