Warnings for apply_numpy_specials depend on order

[michaelaye]

Using pysis 0.5.2

I'm having an issue with Cubefile.apply_numpy_specials.

Apparently the order matters for receiving a warning or not.
Possibly, because your hardcoded Min/Max values don't fit to what I find in this Cassini ISS image?

See screenshot:

[michaelaye]

My RingCube is just a wrapper around your CubeFile for Saturn Ring images, doesn't do anything with your CubeFile inner stuff.

[michaelaye]

could you comment on this?

[wtolson]

I believe the warning is because it is running the comparisons on the special values. This shouldn't cause any problems however it does proabally mean there is a better way to do this.

[michaelaye]

Where did you get those special values from? Are they defined in a standard document somewhere? Possibly either those values need to be updated, or the ISIS routine creating those numbers in the cube, I guess one of them is not consistent with current standards/expectations.

[wtolson]

They're the numpy special values that replace the cube file special values like np.NINF, np.inf and np.nan.

[michaelaye]

I think this is only happening because numpy.less does not like to see the np.nans from the 'Null' replacement, when doing the 'Max' and 'Min' replacement.
As I wrote above, if we do the 'Null' to np.nan replacement at the end, the warning goes away.

Do you see a problem with doing the replacement of Null->np.nan at the end? If not, I can just submit a simple PR to change the order of this.

[michaelaye]

Ok, no, obviously I need to set NANs first, because the minimum is also a negative special pixel value.
But because we know that this operation is working, one should suppress the numpy warning in this case, using np.errstate(invalid='ignore') for those 2 operations. I'll send in a PR.