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From previous ObsParis / CDS meeting

Using Aladin prototype v10 (6/6/2017) and TOPCAT v4.4 on MacOS

Healpix generation from a table

• In TOPCAT load a table containing a list of observations located in lon/lat
(working ex is a large table of VIRTIS observations of 67P)

1) Add new synthetic column providing healpix cell number (right-click on table column header and enter new column description):
healpixNestIndex( 6, longitude, latitude )
(adapt scale to data in use, 6 provides a resolution of ~ 1° at the Equator)

• Open Skyplot planet, add New healpix layer, provide inputs

• Standard setup for planetary maps is (in Axis / Projection):
Projection =  sin (sphere),
Don't reflect longitude axis,
Sky system: Equatorial,
(in Axis / Grid): uncheck sexagesimal

• In Skyplot / Style panel, use Degrade and Combine mode to reduce resolution on the fly.


Mars HiPS generation

• In Aladin, load file Mars_MGS_colorhillshade_mola_1024.jpg

(MOLA integrated relief map)

• Go to Image > astrometric calibration:

Coord = 0.,0.
pos x/y = 512, 256 (lon = 0°, lat = 0° at image center)
size = 21.1' (= 360. / 1024)
Equatorial, Cartesian
Symetry: No => this is mandatory to get the image in the correct orientation.
But this currently provides a W longitude frame (entering Yes results in a reverse image (seen from the inside), not in a reverse frame).

Edit > properties:  ascending longitudes - does not change anything here

• Convert to HiPS :

Tool > Convert current image to a HiPS

• The hpx image should be saved on disk automatically

MOC use case

- Load Mars MOLA hpx in Aladin

- Select two large craters in Mars Craters service from VESPA client

- send as s_region from VESPA client (in Aladin) - s_region currently provided in this service as with W longitude, so this will work

- select them in Aladin with pointer

- Generate common MOC for these 2 craters (Coverage > Generate MOC > from objects)

This works

• Then: test intersections with something else.

How do we do that?

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