deal with nodata in zonal_stats

[martinfleis]

Currently, if you read a geotiff with rioxarray with e.g. -9999 as nodata, zonal_stats uses is as any other value. Need to do something about it.

[dcherian]

There is one challenge here: that -9999 is a NoData value might be out of date by the time xvec gets called.

IMO the only good solution at the moment is to convert to float and use NaN as the NoData value, at least until https://github.com/mdhaber/marray is stable. Otherwise, I guess xvec could accept an optional list of values to ignore.

[martinfleis]

So .rio.nodata is not something to rely on?

xvec could accept an optional list of values to ignore

That was my idea as a fallback but could be the only thing.

[dcherian]

The underlying data may have changed so that the attribute is out of date (e.g. da += 1 :P) or worse, the noData value is suddenly a valid value after some transformation.