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light_travel_time is broken for Time objects with ndim > 1 #5191
Description
Reshaping a Time object to ndim greater than 1 breaks light_travel_time, with the following error:
...
/usr/local/lib/python3.5/site-packages/astropy/coordinates/builtin_frames/icrs_cirs_transforms.py in gcrs_to_icrs(gcrs_coo, icrs_frame)
171 astrom = erfa.apcs13(jd1, jd2, pv)
172
--> 173 i_ra, i_dec = aticq(gcrs_ra, gcrs_dec, astrom)
174
175 if gcrs_coo.data.get_name() == 'unitspherical' or gcrs_coo.data.to_cartesian().x.unit == u.one:
/usr/local/lib/python3.5/site-packages/astropy/coordinates/builtin_frames/utils.py in aticq(ri, di, astrom)
184
185 # Bias-precession-nutation, giving GCRS proper direction.
--> 186 ppr = erfa.trxp(astrom['bpn'], pos)
187
188 # Aberration, giving GCRS natural direction
/usr/local/lib/python3.5/site-packages/astropy/_erfa/core.py in trxp(r, p)
24006
24007 #Create the output array, based on the broadcasted shape, adding the generated dimensions if needed
> 24008 broadcast = numpy.broadcast(numpy.int32(0.0), numpy.int32(0.0), r_in[...,0,0], p_in[...,0])
24009 trp_out = numpy.empty(broadcast.shape + (3,), dtype=numpy.double)
24010
ValueError: shape mismatch: objects cannot be broadcast to a single shape
Activity
StuartLittlefair commentedon Jul 26, 2016
The issue here is a tricky one, arising because the coordinate transformations are not particularly shape-aware.
So at https://github.com/astropy/astropy/blob/master/astropy/time/core.py#L599 we have
which for an (N, M) shaped
Timegives anITRSframe with an (N, M) shapedobstimeattribute and scalarxyzattributes.Then at https://github.com/astropy/astropy/blob/master/astropy/time/core.py#L609 we have
This goes through the transformation
ITRS->CIRS->GCRS. The resultingGCRSframe has (N, M) shapedobstimebut theraanddecproperties are shaped (N*M, ) - as does the intermediateCIRSframe. The next transformation fromGCRStoICRShere inevitably fails because of this mismatch.To solve this issue a large part of the transformation code is going to have to become shape aware, which is a significant code refactor and also should wait until #4123 and #5104 are in, since the refactored code will be much cleaner after code in those PRs has been merged.
StuartLittlefair commentedon Aug 26, 2016
Just to say this issue is magically fixed by #5254.