search

cds-astro / aladin-lite

An astronomical HiPS visualizer in the browser
https://aladin.cds.unistra.fr/AladinLite/
GNU General Public License v3.0
103 stars 42 forks source link

Astrometry offset #193

Open tboch opened 2 months ago

tboch commented 2 months ago

Astrometry accuracy is degraded in v3.4.5 wrt 3.2.0

Here are 2 examples illustrating the issue.

  1. Cassiopea constellation drawing (example https://aladin.cds.unistra.fr/AladinLite/doc/API/examples/polyline/ )

With v3.4.5:

image

With v3.2.0:

image

  1. Zooming on object * bet UMi ( 14 50 42.326 +74 09 19.81 )

Centering the current view on * bet UMi, with AITOFF projection (but the issue is present in all projections, as far as I can tell).

With a 10° FoV , the star is properly centered:

Capture d’écran 2024-08-28 à 11 32 23

With a 32° FoV, the shift is obvious:

Capture d’écran 2024-08-28 à 11 33 04

@bmatthieu3 : could this be linked with some of the astrometric computations having been offloaded to the GPU, when previously

done on the CPU?

bmatthieu3 commented 2 months ago

The accuracy is enhanced since #180 but there is still some deformation present near the healpix poles. We could subdivide the cells but if we do that we must subdivide all the cells in the fov in the same way otherwise we would see frontiers between cells.