Rectify 2D spectrum

[PatrickOgle]

Use spectral trace object to rectify a 2D spectrum by shift-interpolating columns in the spatial direction.
This doesn't require a wavelength solution. This simplest case assumes no mixing of spatial and spectral dimensions.

[PatrickOgle]

This works well, and could form the basis of the algorithm:
center = trace_r.guess
spec2d_rectified = 1.0 *spec2d
for col in range(ncols):
shift = center - trace_r[col]
shifted_col = ndimage.interpolation.shift(spec2d[:,col], shift, order=2)
spec2d_rectified[:,col] = shifted_col