Healpix is a tesselation system on the sphere, depending which depends on a resolution/scale parameter. It provides regular sampling in surface, with no singularity (poles).
The point is to easily get a combined map from sparse data; the result is also scalable in resolution, at least degradation is performed correctly by combining healpix cells.
Cell size (in FoV size, ie in longitude at Equator): scale 6 ~ 1°, 12 ~ 1', 18 ~ 1"
In TOPCAT, load a table containing a list of observations located in lon/lat
(working example is a large table of VIRTIS/Rosetta observations of 67P)
1) Standard way:
• Open Plane Plot panel, select table and Lon & Lat parameters in Position panel
• In the Form panel, you can save the healpix map (cell #, plotting parameter) - saved at scale 12, apparently (FITS formatting is more efficient than VOTable, as it is compressed). You can also load an existing map from there.
• Add new synthetic column providing healpix cell number (right-click on table column header and enter new column description):
HiPS (Hierarchical progressive survey) are associations of healpix maps at different scales. They provide efficient multiresolution scaling on the fly in Aladin.•
1) In Aladin, load file
Mars_MGS_colorhillshade_mola_1024.jpg (MOLA integrated relief map)
• The hpx image should be saved on disk automatically
2) From a series of local files in Aladin
TBC, does not work on my machine.
MOC use case in Aladin
MOC (Multi-Order Coverages) are footprints defined in terms of healpix cells list mixing various resolutions. They provide immediate location information e.g. about intersections.
Should also retain info about original file coverages, for callback purpose.
- Load Mars MOLA hpx in Aladin