New issue 744: Standardize geometry selection https://bitbucket.org/yt_analysis/yt/issue/744/standardize-geometry-selectio... Matthew Turk: Currently, there is some ambiguity in how the lengths are passed in in the selection routines. For the most part, everything is (currently) done correctly in "code_length" units, but this needs to be made explicit. "code_length" itself is no longer mandated to be a part of the lookup registry. This was to prevent errors. I think that we may eventually want to mandate everything in "unitary", but for now I will attempt to implement in "code_length" in the Cython code. To complete this, essentially every place in `yt/geometry/selection_routines.pyx` that a geometric ndarray is accessed will need to be converted to "code_length". I am inclined to think that we can use in-place conversions here, to avoid making duplicates of the arrays (which may be large). Responsible: MatthewTurk