BUG: method='sum' does not work for off-axis projections

[chrishavlin]

The off-axis projections don't really work with method='sum':

import yt 
from yt.testing import fake_amr_ds

ds = fake_amr_ds()

field = ('index', 'ones')
p = yt.OffAxisProjectionPlot(ds, [0., 0., 1], field, method='sum', width = 2., buff_size=(400,400))
p.set_log(field, False)
p.save('/var/tmp/method_sum_offaxis_but_aligned.png')

This should return the same as the axis-aligned version

p = yt.ProjectionPlot(ds, 'z', field, method='sum', width = 2., buff_size=(400,400))
p.set_log(field, False)
p.save('/var/tmp/method_sum_axis_aligned.png')

Note that this isn't a high priority since method='sum' is not usually the correct choice for analysis... but it would have been useful for some tests that I was writing.

[chrishavlin]

i did look very briefly at the reason -- and it's because the volume rendering sampling methods used for off-axis projections always integrate (multiply by path length in the intersected element), they're just not set up for simply summing. Which is fine, it's OK for this to not work I think since as I said it's probably only really useful for tests that aren't really physical (but we may want to mention it in the documentation).

[cphyc]

Could you check for octree datasets?

[chrishavlin]

sure, will do! i only looked at the standard gridded dataset (which end up using the KDTree volume sampler). definitely worth trying an octree ds too, will let you know how it goes when i get to it.