On Tue, 16 Dec 2003, Tim Jenness wrote:
> Our new correlator, ACSIS, by default generates cubes using a CAR
> projection for the spatial axis. We are having a lot of trouble finding
> applications that report the RA/Dec correctly for this projection at the
> pole.
>
> We have 3 example files:
>
> near_pol_map.fits -> SIN projection
> near_pol_map_car.fits -> CAR projection
> near_pol_map_mer.fits -> MER projection
>
> Available from
>
> http://www.jach.hawaii.edu/~timj/proj.tar.gz
>
> All have [1,1,1] set at 05:20:04.000 +89.59.00.000 6.914730e+11 Hz
> [The spectral headers are not liked by AST v3 so I need to look into
> that].
>
> You'll be pleased to hear that GAIA does correctly report the
> RA/Dec for CAR as the pole is crossed but the axis overlay is not quite
> correct since it stops at +90 and does not draw in the top half of the
> grid. I assume this is because of the RA discontinuity. Any chance that
> could be fixed?
Probably, currently GAIA makes all CAR projections work just like linear
projections. See the AST attibute:
% showme sun211 CarLin
GAIA has this set permanently true at present (compatibility seems more
important). If I switch this off I get the image attached. Is that what
you expected?
> Also, the projection information is not reported in the
> title (it's written as <null>) for all of the test images.
>
> Jamie reports that the MER projection seesm to fail completely. FV
> displays it fine but it seems to display as a SIN projection in GAIA. Is
> AST meant to support MER?
Yes, again I don't what you expected to see, but GAIA produced the
attached image.
No doubt David B. will enlighten you further.
Peter.
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