EPN2020-RI

EUROPLANET2020 Research Infrastructure 

H2020-INFRAIA-2014-2015 

Grant agreement no: 654208

Document: VESPA-WP11-2-016-TN-v0.5(47)

Planetary Coordinate Systems

Date: 02 Jun 2017 

Responsible WP Leader: Stéphane Erard

Table of Contents

1 - Introduction

The EPN-TAP protocol is directly derived from IVOA’s TAP [RD3], a simple protocol to access data organized in tables, here adapted for Planetary Science data. EPN-TAP and its implicit Data Model EPNcore are described in [RD1]. A more comprehensive Data Model for Planetary Science is also available [RD2].  

In the EPN-TAP protocol, the data files are described in a table named epn_core by a set of mandatory parameters. The spatial_frame_type parameter provides the general “flavor” of the coordinate system, and can have the following values: celestial, body, cartesian, cylindrical, spherical, healpix. This parameter defines the nature of the 3 spatial coordinates (named c1,c2,c3).

When using some values of the spatial_frame_type parameter, the spatial_origin and spatial_coordinate_description parameters allow the data provider to specify the exact coordinate system used in the data set (including altitude). The system in use is known by the data provider, and the parameters are essentially intended to provide this information to the user for comparison with other data sets. In the future, this information could be used to perform automatic coordinate conversions.

The present document lists possible values for these parameters. The values listed here are adapted from the IAU Working Group on Cartographic Coordinates and Rotational Elements reports [RD5], the Space-Time Coordinates (STC) document from IVOA [RD4], the PDS standard reference, chap. 2 [RD6], and various references mentioned in the text. All values in the epn_core table should be provided in lower cases; all longitudes are expected to range from 0° to 360° eastward.

2 - Coordinate systems

2.1 Native coordinates

Data are projected in a frame related to the instrument or acquisition process.

Typical examples include: X/Y coordinates for a camera, X/time coordinates for an imaging spectrometer.

Possible situation:

spatial_frame_type = cartesian

spatial_coordinate_description = native

Are Spice instrument-frame names acceptable?

Practically, it means that data products are provided in a native instrument frame, and therefore are not spatially registered – they are not searchable on a coordinate basis in general.

2.2 Astronomical / telescopic coordinates

This situation is identified by:

spatial_frame_type = celestial

This provides 2 angles + 1 optional distance counted from the origin.

It is assumed that horizontal, ecliptic and galactic coordinates are provided with no explicit mention of epoch (which can be retrieved from the date of observation if need be).

The STC [RD4] distinguishes 3 types of equatorial systems:

The reference position is provided through the spatial_origin parameter.

Values of interest from the STC [RD4] (table 1) are:

Can all value(s) for spacecraft, planetary landers, and orbital telescopes (with moving origin) be accessed through TOPOCENTER, or RELOCATABLE? — PDS3 uses a SPACECRAFT value.

+ Can an ephemeris file be provided for moving locations?

2.3 Solid bodies

This situation is identified by:

spatial_frame_type = body

Provides 2 angles + 1 optional distance (not necessarily from body center, therefore not consistent with the STC).

Coordinate systems may differ by the assumed shape of the body, its rotational elements, the location of the prime meridian, the control point network in use, and the definition of latitudes.

Body fixed reference frames:

Frames are defined through shape / rotational elements in [RD5]  

            http://astrogeology.usgs.gov/Page/groups/name/IAU-WGCCRE

+ reference geoid models for the Earth?

Standard planetary coordinate systems and reference ellipsoids are listed here (IAU doc –older systems are not included):

            http://planetarynames.wr.usgs.gov/TargetCoordinates

Control networks used are important to mention for high-resolution imaging.

Information about Control Networks can be found here (USGS):

            http://astrogeology.usgs.gov/maps/control-networks

The values mentioned in this and other sources are:

Moon:

ULCN1994— Unified Lunar Control Network (1994)

CLCN — related to Clementine Basemap, 1997

ULCN2004 — Unified ULCN1994 and CLCN, 2004

LOLCN — related to Lunar Orbiter images, 2004

ULCN2005 — Unified Lunar Control Network revised, 2005 (?)

LOLA2011 – Lunar Orbiter, 2011

Mars:

Control Networks are referred to the Digital Image Model first using them.

MDIM — Original Viking mosaics

MDIM2.0 — Mars Digital Image Mosaic (MDIM) 2.0 control network

MDIM2.1 — Mars control network tied to the MOLA Digital Elevation Model

http://www.isprs.org/proceedings/XXXV/congress/comm4/papers/464.pdf

Actual map projections are listed here (ie, list of existing surface maps):            https://astrocloud.wr.usgs.gov/index.php?view=pow

+ see http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1931.pdf

for possible use in OGC

Coordinate systems may be planetocentric (defined relative to a vector passing by the center of mass) or planetographic (defined relative to the local horizontal plane), resulting in different latitudes if the body is not spherical.

Coordinate systems may be defined as east-handed or west-handed. In the IAU 2000 standard, planetocentric systems must be east-handed for planets and satellites. In any case, the epn_core table must contain a version with eastward longitudes ranging from 0° to 360°, in order to handle EPN-TAP queries without ambiguity.

Possible nomenclature:

Target + IAU + year of introduction?            => Mars_IAU2000

Does not tell if this is planetocentric/graphic?

Spice names look like IAU_Mars (= always the latest version implied)

References for small bodies

According to IAU standards, small bodies are all considered prograde and their north pole is defined accordingly.

Coordinate system name should state shape model/prime meridian in use?

The STC document distinguishes 2 options related to the meaning of the third coordinate:

To be introduced through the spatial_origin parameter??

In many cases the surface is used as origin, e.g., in atmospheric databases – this corresponds to the geodetic option above.

+ Need different origin for planetographic coordinates?

2.4 Giant planets

This situation is identified by:

spatial_frame_type = body

Provides 2 angles + 1 optional distance (from body center, for consistency with STC?? TBC)

STC distinguishes between planetographic and planetocentric:

In the PDS3 standard reference there is only one value for each planet in the coordinate_system_ID keyword:

    "-JUPSYS3", "-SATSYS3", "-URNSYS3" + VSO

2.5 Plasma / dynamic coordinates

This situation may correspond to

spatial_frame_type = cartesian or spherical

From STC document:

2.6 Magnetospheric coordinates

This situation may correspond to

spatial_frame_type = cartesian or spherical

Three types of reference frames are used:

-      planetocentric solar magnetic (X towards Sun; Z towards planetary magnetic North pole). Only exist when the body has an intrinsic magnetic field.

-      planetocentric solar equatorial (X towards Sun; Z perpendicular to the equator of the planet, towards the planetary North pole)

-      planetocentric solar ecliptic (X towards the Sun; Z perpendicular to ecliptic plane, in the northern celestial hemisphere)

Each of them is centered on the planet barycenter. Y axis is completing the orthogonal direct reference frames.

2.7 Landers/rovers coordinates

This specific situation is expected to be correctly described in the PDS3/4 reference, TBC.

2.8 Solar-terrestrial interactions

Derived from a SPASE document compiling various sources.

[1] http://www.spase-group.org/data/search.jsp?term=Coordinate+System+Name&style=entry&scope=dictionary&version=2.2.0

[2] http://omniweb.gsfc.nasa.gov/vitmo/cgmm_des.html 

[3] https://cdpp-archive.cnes.fr/project/data/documents/PLAS-LO-ROCOTLIB-00428-CET/00428.pdf and software libraries in IDL (tar) or Fortran (tar)

[4] C.T. Russell, (1971) "Geophysical Coordinate Transformations", Cosmic. Electrodyn. 2, 184-196. URL: http://www-ssc.igpp.ucla.edu/personnel/russell/papers/gct1.html

[5] M.A. Hapgood, (1992) "Space Physics Coordinate Transformations: A User Guide", Planet. Space Sci. 40, 711-717.
M.A. Hapgood, (1997) "Corrigendum to Space Physics Coordinate Transformations: A User Guide", Planet. Space Sci. 45, 1047. 

[6] http://cohoweb.gsfc.nasa.gov/helios/coor_des.html

[7] http://sspg1.bnsc.rl.ac.uk/SEG/Coordinates/refs.htm

[8] http://stereo-ssc.nascom.nasa.gov/coordinates_explanation.shtml

[9] http://www.spenvis.oma.be/help/background/coortran/coortran.html

[10] http://www.srl.caltech.edu/ACE/ASC/coordinate_systems.html

[11] M.Fraenz and D.Harper, Heliospheric Coordinate Systems, Planet. Space Sci., 50, 217-233 (Feb 2002). URL: http://www.mps.mpg.de/homes/fraenz/systems/

[12] http://helio-vo.eu/documents/public/HELIO_Coordinates_100322.pdf

[13] Thompson, W. T. Coordinate systems for solar image data. A&A 449, 791–803 (2006). http://www.aanda.org/10.1051/0004-6361:20054262

2.9 Jovian Systems

from Fraenz and Harper (2002):

2.10 SPICE Built-in Frames

From SPICE Ref Manual:

• Inertial Frames (ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/frames.html#Appendix.%20``Built%20in''%20Inertial%20Reference%20Frames)
• IAU Body fixed frames (ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/frames.html#Appendix.%20``Built%20in''%20PCK-Based%20IAU%20Body-Fixed%20Reference%20Frames)

List of IAU-Body-Fixed reference frames: IAU_ADRASTEA, IAU_AMALTHEA, IAU_ANANKE, IAU_ARIEL, IAU_ATLAS, IAU_BELINDA, IAU_BENNU, IAU_BIANCA, IAU_BORRELLY, IAU_CALLIRRHOE, IAU_CALLISTO, IAU_CALYPSO, IAU_CARME, IAU_CERES, IAU_CHALDENE, IAU_CHARON, IAU_CORDELIA, IAU_CRESSIDA, IAU_DAVIDA, IAU_DEIMOS, IAU_DESDEMONA, IAU_DESPINA, IAU_DIONE, IAU_EARTH, IAU_ELARA, IAU_ENCELADUS, IAU_EPIMETHEUS, IAU_ERINOME, IAU_EROS, IAU_EUROPA, IAU_GALATEA, IAU_GANYMEDE, IAU_GASPRA, IAU_HARPALYKE, IAU_HELENE, IAU_HIMALIA, IAU_HYPERION, IAU_IAPETUS, IAU_IDA, IAU_IO, IAU_IOCASTE, IAU_ISONOE, IAU_ITOKAWA, IAU_JANUS, IAU_JULIET, IAU_JUPITER, IAU_KALYKE, IAU_LARISSA, IAU_LEDA, IAU_LUTETIA, IAU_LYSITHEA, IAU_MAGACLITE, IAU_MARS, IAU_MERCURY, IAU_METIS, IAU_MIMAS, IAU_MIRANDA, IAU_MOON, IAU_NAIAD, IAU_NEPTUNE, IAU_NEREID, IAU_OBERON, IAU_OPHELIA, IAU_PALLAS, IAU_PAN, IAU_PANDORA, IAU_PASIPHAE, IAU_PHOBOS, IAU_PHOEBE, IAU_PLUTO, IAU_PORTIA, IAU_PRAXIDIKE, IAU_PROMETHEUS, IAU_PROTEUS, IAU_PUCK, IAU_RHEA, IAU_ROSALIND, IAU_SATURN, IAU_SINOPE, IAU_STEINS, IAU_SUN, IAU_TAYGETE, IAU_TELESTO, IAU_TEMPEL_1, IAU_TETHYS, IAU_THALASSA, IAU_THEBE, IAU_THEMISTO, IAU_TITAN, IAU_TITANIA, IAU_TRITON, IAU_UMBRIEL, IAU_URANUS, IAU_VENUS, IAU_VESTA.

2.11 Galilean Moon Frames

• Source = PDS Data_set_id = GO-J-POS-6-SC-TRAJ-MOON-COORDS-V1.0
• Current URL: https://pds.nasa.gov/ds-view/pds/viewDataset.jsp?dsid=GO-J-POS-6-SC-TRAJ-MOON-COORDS-V1.0

Two coordinate systems are provided:

• SPRH (Satellite centered planetocentric, right-handed),
• PhiO (Satellite centered inertial Phi-Omega coordinates),

Distances from the satellites are measured in satellite radii. The radii values used for the various satellites are listed in the following Table:

Satellite centered coordinate systems names are preceded by the first letter in the name of the satellite, in order to indicate which satellite is used as the center. In order words, PhiO coordinates are called EPhiO at Europa and CPhiO at Callisto

SPRH (Satellite centered planetocentric, right-handed)

This coordinate system is the basic J2000 definition of planetocentric coordinates, as applied to each of the satellites. In it's Cartesian form the coordinate system has its Z-axis along the satellite axis of rotation positive in the direction of angular momentum, the X-axis in the equatorial plane in the direction of the prime meridian, with the Y-axis completing the right-handed set. The coordinate system rotates with the satellite (body-fixed).

All of the SPRH data in this data set are based on the International Astronomical Union (IAU) definitions of the satellite axes orientations and rotation rates from the Report of the IAU/IAG/COSPAR Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites: 1994 [IAU1994]. The specific orbit elements for each satellite are summarized in the following Table:

* PM = const + rate*d where d is days after the J2000 epoch.

PhiO (Satellite centered inertial Phi-Omega coordinates)

The basis vectors of the inertial Phi-Omega coordinate systems are defined at an epoch time that is set at the time of spacecraft closest approach to the satellite. The X-direction is defined to be in the direction of corotation, at the center of the satellite at the epoch time (System III Phi direction [DESSLER1983]). The Z-axis is defined to be orthogonal to the X direction such that the X-Z plane contains the Jupiter spin axis (Omega), positive in the direction of angular momentum. The Y-axis is defined to complete the right-handed set. Since the jovian satellites all lie very close to the jovian equatorial plane, it is often convenient to visualize this coordinate system as follows: X lies in the direction of plasma flow, Y points towards Jupiter, and Z points 'up'.

2.12 Anything else?

Comets maybe?