[fitsbits] multidimensional rotations

[Steve Allen]

On Tue 2017-10-31T17:42:22+0100 Walter Jaffe hath writ:
> I attach some thoughts about the best way to represent completely general
> rotations in dimensions > 2.

For the Keck and Lick instruments we have never used CROTAi and we
have never used PCi_j.  We have stopped inserting CDELTi, thus their
values default to 1.0.  We rely entirely on CDi_j as a general linear
transformation which usually includes shear as well as rotation and
scale.

I am quite fond of the notion that it is theoretically possible to
decompose the aberrations of relativity, atmosphere, and instrument
into normal and orthonormal transformations.  In practice I have not
found that this is useful with observed data, so I concur with the
conclusion that the urgency to change the status quo is low.

--
Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
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