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From previous ObsParis / CDS meeting

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

Standard planetary mapping in TOPCAT

Assuming longitude is E-handed (EPN-TAP convention, and IAU convention in planetocentric frames)

• Standard setup for planetary maps in TOPCAT SkyPlot is:

(in Axes / Projection)
Projection =  sin (i.e., sphere),
Uncheck Reflect longitude axis,
View Sky System: Equatorial,

(in Axis / Grid)
Uncheck Sexagesimal
Increase Grid Crowding cursor value to 30 or 60° tick

• Standard setup for planetary maps in TOPCAT PlanePlot is:

(in Axes / Range)
Set Max X value to 360
Central meridian will  be on left side

• To put Central meridian at the center:

(in Axes / Range)
Min / Max X = -180 / 180

(in Mark / Position)
X: LON > 180 ? Lon - 360 : Lon

(in Axes / Labels)
X Label = Longitude

Healpix generation from a table in TOPCAT

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

• Go to Form panel, click on the big Forms button (green cross) and "Add SkyDensity" from the local menu. Uncheck the previous Mark Form

• Go back to Position panel, select Lon and Lat parameters (C1min and C2min for an EPN-TAP view)

• Back to the Form panel, select parameter to plot as Weight (will be weighted by density), select combine mode, and adjust scale. Healpix generation is performed on the fly.

• Possibly adapt color scale in the Aux Axis tab (left menu)

• 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.


2) Alternatively:

• 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 panel, add New healpix layer, provide inputs
Correct Healpix Data Level in particular (TOPCAT will try to guess, but this is uncertain)

• 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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