Update tile retreival ahn.py

[bdestombe]

• On the eclipse server: Skip tile retreival if the link does not exist.
• Legacy server: Rasterio merge returned only zero's since 17 sept. All the merging is now done within xarray.

[rubencalje]

Great.

I would just leave the old method (_download_and_combine_tiles) intact, and not change anything. With the proposed changes, and when as_data_array is False, you return something else as before . This method is just for people who wish to use the exact same output as before, using the legacy-methods. So changing its output-type is kind of contradictory to this. In a few versions, we will remove the legacy-methods and _download_and_combine_tiles.

[bdestombe]

Well could you maybe confirm? If I use _download_and_combine_tiles(), during the merge command of rasterio all values are converted to 0. With the proposed changes the function works like intended.

[bdestombe]

Since no error is produced and zeros are falsely returned, I would suggest to either

• already remove these functions,
• keep these functions as legacy functions with an additional warning that their outcome is wrong
• keep these suggested changes

[rubencalje]

The zeros are caused by rasterio version 1.3.11, and you do get a warning (see issue #369). We changed the normal versions of the methods to use the xarray-merge to solve this bug. However, some people might want to use the old server, or as_data_array=False. Therefore, the old methods are still available using the _legacy-suffix. However, I do not think we should maintain these methods. This will introduce additional work and errors.

For example. With the proposed changes, the following code

import nlmod
extent = [100_000, 110_000, 400_000, 405_000]
nlmod.read.ahn.get_ahn4_legacy(extent)

produces

<xarray.DataArray 'band_data' (band: 1, y: 0, x: 2000)> Size: 0B
array([], shape=(1, 0, 2000), dtype=float32)
Coordinates:
  * band         (band) int32 4B 1
  * x            (x) float64 16kB 1e+05 1e+05 1e+05 ... 1.1e+05 1.1e+05 1.1e+05
  * y            (y) float64 0B 
    spatial_ref  int32 4B 0
Attributes:
    AREA_OR_POINT:  Area

So this is an empty data-array (while the original methods produce the correct data-array, with non-zero data if you do not use rasterio 1.3.11). We can off course fix this issue as well, but this is not the goal of the legacy-methods.

[bdestombe]

Thanks Ruben for taking the time. I was falsely under the impression that the all-zeros-bug also appeared with other versions of rasterio. I will revert the code and merge the two remaining lines.

Edit: I was mixing up rioxarray and rasterio packages when checking the behavior for different versions.. With rasterio version 1.3.11 and changing versions of rioxarray the all-zeros-bug of course remains