cross_axis_slope vs cross_axis_tilt

[williamhobbs]

pvlib.shading.shaded_fraction1d uses 'cross_axis_slope' as an input, while pvlib.tracking.singleaxis uses 'cross_axis_tilt'. I think these are the same thing - is that correct? If so, would it make sense to update one of them to be consistent?

I couldn't seem to find any discussion of this in related PRs, but apologies if I just missed it.

tagging @kandersolar, @mikofski, @AdamRJensen, and @echedey-ls, since you all worked on these functions and/or references.

[kandersolar]

Yes, they represent the same quantity. That they have different names in those two functions was an oversight, and a shame. Thanks for pointing it out.

I'd have to think a bit more to form an opinion on which of them should be changed to match the other.

[mikofski]

I am minus one against “tilt” because the cross axis slope is the angle between adjacent rows. In my opinion tilt refers to the orientation of a tracker axis or module surface.

[kandersolar]

"tilt" also tends to be a non-negative quantity in pvlib, whereas cross_axis_X can be positive or negative.

"slope" has the downside of potentially being interpreted as "grade", i.e. rise over run (rather than the arctan of rise over run).

Other places the "tilt" variant appears:

• name of pvlib.tracking.calc_cross_axis_tilt
• parameter of pvlib.pvsystem.SingleAxisTrackerMount

[echedey-ls]

So, shall we change it? I prefer to do that sooner than later, but I don't see any strong opinion (nor I have one). We can even consider cross_axis_rotation to address the well-reasoned comment above me.

[williamhobbs]

I prefer cross_axis_slope.

"slope" has the downside of potentially being interpreted as "grade"

Hopefully documentation will be very clear about units.

We can even consider cross_axis_rotation

I can't help but think of tracker rotation.

To address the concern about confusing an angle with a grade, we could consider cross_axis_slope_angle or cross_axis_angle, but I still like cross_axis_slope the best.