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SuperNOVAS: src/observer.c File Reference

Date

Created on Mar 6, 2025

Function that define an astronomical observer location or are related to observer location.

Corrects position vector for aberration of light. Algorithm includes relativistic terms.

NOTES:

1. This function is called by place() to account for aberration when calculating the position of the source.

REFERENCES:

1. Murray, C. A. (1981) Mon. Notices Royal Ast. Society 195, 639-648.
2. Kaplan, G. H. et. al. (1989). Astron. Journ. 97, 1197-1210.

Parameters

pos [AU] Position vector of source relative to observer vobs [AU/day] Velocity vector of observer, relative to the solar system barycenter, components in AU/day. lighttime [day] Light time from object to Earth in days (if known). Or set to 0, and this function will compute it. [out] out [AU] Position vector, referred to origin at center of mass of the Earth, corrected for aberration, components in AU. It can be the same vector as one of the inputs.

Returns

0 if successful, or -1 if any of the vector arguments are NULL.

See also

place()

References novas_vlen().

Moves the origin of coordinates from the barycenter of the solar system to the observer (or the geocenter); i.e., this function accounts for parallax (annual+geocentric or just annual).

REFERENCES:

1. Kaplan, G. H. et. al. (1989). Astron. Journ. 97, 1197-1210.

Parameters

pos [AU] Position vector, referred to origin at solar system barycenter, components in AU. pos_obs [AU] Position vector of observer (or the geocenter), with respect to origin at solar system barycenter, components in AU. [out] out [AU] Position vector, referred to origin at center of mass of the Earth, components in AU. It may be NULL if not required, or be the same vector as either of the inputs. [out] lighttime [day] Light time from object to Earth in days. It may be NULL if not required.

Returns

0 if successful, or -1 if any of the essential pointer arguments is NULL.

See also

place()

light_time2()

References novas_vlen().

Computes the geocentric position of a solar system body, as antedated for light-time.

Parameters

jd_tdb [day] Barycentric Dynamical Time (TDB) based Julian date body Pointer to structure containing the designation for the solar system body pos_obs [AU] Position 3-vector of observer (or the geocenter), with respect to origin at solar system barycenter, referred to ICRS axes, components in AU. tlight0 [day] First approximation to light-time, in days (can be set to 0.0 if unknown). accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) [out] pos_src_obs [AU] Position 3-vector of body, with respect to origin at observer (or the geocenter), referred to ICRS axes, components in AU. It can be the same vector as either of the inputs. [out] tlight [day] Calculated light time

Returns

0 if successful, -1 if any of the poiinter arguments is NULL, 1 if the algorithm failed to converge after 10 iterations, or 10 + the error from ephemeris().

See also

light_time2()

place()

References light_time2().

Computes the geocentric position and velocity of a solar system body, as antedated for light-time. It is effectively the same as the original NOVAS C light_time(), except that this returns the antedated source velocity vector also.

NOTES:

1. This function is called by place() to calculate observed positions, radial velocity, and distance for the time when the observed light originated from the source.

Parameters

jd_tdb [day] Barycentric Dynamical Time (TDB) based Julian date body Pointer to structure containing the designation for the solar system body pos_obs [AU] Position 3-vector of observer (or the geocenter), with respect to origin at solar system barycenter, referred to ICRS axes, components in AU. tlight0 [day] First approximation to light-time, in days (can be set to 0.0 if unknown). accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) [out] p_src_obs [AU] Position 3-vector of body, relative to observer, referred to ICRS axes, components in AU. [out] v_ssb [AU/day] Velocity 3-vector of body, with respect to the Solar-system barycenter, referred to ICRS axes, components in AU/day. [out] tlight [day] Calculated light time, or NAN when returning with an error code.

Returns

0 if successful, -1 if any of the pointer arguments is NULL or if the output vectors are the same or if they are the same as pos_obs, 1 if the algorithm failed to converge after 10 iterations, or 10 + the error from ephemeris().

See also

light_time()

place()

Since

1.0

Author

Attila Kovacs

References bary2obs(), ephemeris(), NOVAS_BARYCENTER, NOVAS_FULL_ACCURACY, and novas_inv_max_iter.

Populates an 'observer' data structure for an observer moving relative to the surface of Earth, such as an airborne observer. Airborne observers have an earth fixed momentary location, defined by longitude, latitude, and altitude, the same was as for a stationary observer on Earth, but are moving relative to the surface, such as in an aircraft or balloon observatory.

Parameters

location Current longitude, latitude and altitude, and local weather (temperature and pressure) vel [km/s] Surface velocity. [out] obs Pointer to data structure to populate.

Returns

0 if successful, or -1 if the output argument is NULL.

See also

make_observer_at geocenter()

make_observer_in_space()

make_observer_on_surface()

make_solar_system_observer()

novas_calc_geometric_position()

place()

Since

1.1

Author

Attila Kovacs

References IN_SPACE_INIT, make_observer(), NOVAS_AIRBORNE_OBSERVER, and in_space::sc_vel.

Populates an 'in_space' data structure, for an observer situated on a near-Earth spacecraft, with the provided position and velocity components. Both input vectors are assumed with respect to true equator and equinox of date.

Parameters

sc_pos [km] Geocentric (x, y, z) position vector in km. NULL defaults to the origin sc_vel [km/s] Geocentric (x, y, z) velocity vector in km/s. NULL defaults to zero speed. [out] loc Pointer to earth-orbit location data structure to populate.

Returns

0 if successful, or -1 if the output argument is NULL.

See also

make_observer_in_space()

make_on_surface()

IN_SPACE_INIT

References in_space::sc_pos, and in_space::sc_vel.

Populates an 'observer' data structure given the parameters. The output data structure may be used an the the inputs to NOVAS-C function 'place()'.

Parameters

where The location type of the observer loc_surface Pointer to data structure that defines a location on Earth's surface. Used only if 'where' is NOVAS_OBSERVER_ON_EARTH, otherwise can be NULL. loc_space Pointer to data structure that defines a near-Earth location in space. Used only if 'where' is NOVAS_OBSERVER_IN_EARTH_ORBIT, otherwise can be NULL. [out] obs Pointer to observer data structure to populate.

Returns

0 if successful, -1 if a required argument is NULL, or 1 if the 'where' argument is invalid.

See also

make_observer_at_geocenter()

make_observer_on_surface()

make_observer_in_space()

make_solar_system_observer()

References observer::near_earth, NOVAS_AIRBORNE_OBSERVER, NOVAS_OBSERVER_AT_GEOCENTER, NOVAS_OBSERVER_IN_EARTH_ORBIT, NOVAS_OBSERVER_ON_EARTH, NOVAS_SOLAR_SYSTEM_OBSERVER, observer::on_surf, in_space::sc_vel, and observer::where.

Populates an 'observer' data structure, for an observer situated on a near-Earth spacecraft, with the specified geocentric position and velocity vectors. Both input vectors are with respect to true equator and equinox of date. The output data structure may be used an the the inputs to NOVAS-C function 'place()'.

Parameters

sc_pos [km] Geocentric (x, y, z) position vector in km. sc_vel [km/s] Geocentric (x, y, z) velocity vector in km/s. [out] obs Pointer to the data structure to populate

Returns

0 if successful, or -1 if the output argument is NULL.

See also

make_observer_on_surface()

make_observer_at_geocenter()

place()

References make_in_space(), make_observer(), and NOVAS_OBSERVER_IN_EARTH_ORBIT.

Populates and 'on_surface' data structure with the specified location defining parameters of the observer. The output data structure may be used an the the inputs to NOVAS-C function 'place()'.

Parameters

latitude [deg] Geodetic (ITRS) latitude in degrees; north positive. longitude [deg] Geodetic (ITRS) longitude in degrees; east positive. height [m] Altitude over se level of the observer (meters). temperature [C] Temperature (degrees Celsius). pressure [mbar] Atmospheric pressure (millibars). [out] obs Pointer to the data structure to populate.

Returns

0 if successful, or -1 if the output argument is NULL.

See also

make_observer_in_space()

make_observer_at_geocenter()

place()

References make_observer(), make_on_surface(), and NOVAS_OBSERVER_ON_EARTH.

Populates an 'on_surface' data structure, for an observer on the surface of the Earth, with the given parameters.

Note, that because this is an original NOVAS C routine, it does not have an argument to set a humidity value (e.g. for radio refraction). As such, the humidity value remains undefined after this call. To set the humidity, set the output structure's field after calling this funcion. Its unit is [%], and so the range is 0.0–100.0.

NOTES

1. This implementation breaks strict v1.0 ABI compatibility since it writes to (initializes) a field (humidity) that was not yet part of the on_surface structure in v1.0. As such, linking SuperNOVAS v1.1 or later with application code compiled for SuperNOVAS v1.0 can result in memory corruption or segmentation fault when this function is called. To be safe, make sure your application has been (re)compiled against SuperNOVAS v1.1 or later.

Parameters

latitude [deg] Geodetic (ITRS) latitude in degrees; north positive. longitude [deg] Geodetic (ITRS) longitude in degrees; east positive. height [m] Altitude over sea level of the observer (meters). temperature [C] Temperature (degrees Celsius) [-120:70]. pressure [mbar] Atmospheric pressure (millibars) [0:1200]. [out] loc Pointer to Earth location data structure to populate.

Returns

0 if successful, or -1 if the output argument is NULL, or if the temperature or pressure values are impossible for an Earth based observer.

See also

make_observer_on_surface()

make_in_space()

ON_SURFACE_INIT

ON_SURFACE_LOC

Populates an 'observer' data structure, for an observer situated on a near-Earth spacecraft, with the specified geocentric position and velocity vectors. Solar-system observers are similar to observers in Earth-orbit but their momentary position and velocity is defined relative to the Solar System Barycenter, instead of the geocenter.

Parameters

sc_pos [AU] Solar-system barycentric (x, y, z) position vector in ICRS. sc_vel [AU/day] Solar-system barycentric (x, y, z) velocity vector in ICRS. [out] obs Pointer to the data structure to populate

Returns

0 if successful, or -1 if the output argument is NULL.

See also

make_observer_in_space()

make_observer_on_surface()

make_observer_at_geocenter()

make_airborne_observer()

novas_calc_geometric_position()

place()

Since

1.1

Author

Attila Kovacs

References make_in_space(), make_observer(), and NOVAS_SOLAR_SYSTEM_OBSERVER.

Converts coordinate offsets, from the local equatorial system to local horizontal offsets. Converting between local flat projections and spherical coordinates usually requires a WCS projection.

REFERENCES:

1. Calabretta, M.R., & Greisen, E.W., (2002), Astronomy & Astrophysics, 395, 1077-1122.

Parameters

dra [arcsec] Projected ffset position in the apparent true-of-date R.A. direction. E.g. The projected offset between two RA coordinates at a same reference declination, is δRA = (RA2 - RA1) * cos(Dec₀) ddec [arcsec] Projected offset position in the apparent true-of-date declination direction. pa [deg] Parallactic Angle [out] daz [arcsec] Output offset position in the local azimuth direction. It can be a pointer to one of the input coordinates, or NULL if not required. [out] del [arcsec] Output offset position in the local elevation direction. It can be a pointer to one of the input coordinates, or NULL if not required.

Returns

0

Since

1.3

Author

Attila Kovacs

See also

novas_h2e_offset()

novas_epa()

References novas_h2e_offset().

Returns the equatorial Parallactic Angle (PA) calculated for an R.A./Dec location of the sky at a given sidereal time. The PA is the angle between the local horizontal coordinate directions and the local true-of-date equatorial coordinate directions, at the given location and time. The polar wobble is not included in the calculation.

The Parallactic Angle is sometimes referrred to as the Vertical Position Angle (VPA). Both define the same quantity.

Parameters

ha [h] Hour angle (LST - RA) i.e., the difference between the Local (apparent) Sidereal Time and the apparent (true-of-date) Right Ascension of observed source. dec [deg] Apparent (true-of-date) declination of observed source lat [deg] Geodetic latitude of observer

Returns

[deg] Parallactic Angle (PA). I.e., the clockwise position angle of the elevation direction w.r.t. the declination axis in the equatorial system. Same as the clockwise position angle of the declination direction w.r.t. the elevation axis, in the horizontal system.

Since

1.3

Author

Attila Kovacs

See also

novas_hpa()

novas_lst()

novas_e2h_offset()

Converts coordinate offsets, from the local horizontal system to local equatorial offsets. Converting between local flat projections and spherical coordinates usually requires a WCS projection.

REFERENCES:

1. Calabretta, M.R., & Greisen, E.W., (2002), Astronomy & Astrophysics, 395, 1077-1122.

Parameters

daz [arcsec] Projected offset position in the azimuth direction. The projected offset between two azimuth positions at the same reference elevation is δAz = (Az2 - Az1) * cos(El₀). del [arcsec] projected offset position in the elevation direction pa [deg] Parallactic Angle [out] dra [arcsec] Output offset position in the local true-of-date R.A. direction. It can be a pointer to one of the input coordinates, or NULL if not required. [out] ddec [arcsec] Output offset position in the local true-of-date declination direction. It can be a pointer to one of the input coordinates, or NULL if not required.

Returns

0

Since

1.3

Author

Attila Kovacs

See also

novas_e2h_offset()

novas_hpa()

Returns the horizontal Parallactic Angle (PA) calculated for a gorizontal Az/El location of the sky. The PA is the angle between the local horizontal coordinate directions and the local true-of-date equatorial coordinate directions at the given location. The polar wobble is not included in the calculation.

The Parallactic Angle is sometimes referrred to as the Vertical Position Angle (VPA). Both define the same quantity.

Parameters

az [deg] Azimuth angle el [deg] Elevation angle lat [deg] Geodetic latitude of observer

Returns

[deg] Parallactic Angle (PA). I.e., the clockwise position angle of the declination direction w.r.t. the elevation axis in the horizontal system. Same as the the clockwise position angle of the elevation direction w.r.t. the declination axis in the equatorial system.

Since

1.3

Author

Attila Kovacs

See also

novas_epa()

novas_h2e_offset()

Converts a 3D line-of-sight vector (δφ, δθ δr) to a rectangular equatorial (δx, δy, δz) vector.

Parameters

los [arb.u.] Line-of-sight 3-vector (δφ, δθ δr). lon [deg] Line-of-sight longitude. lat [deg] Line-of-sight latitude. [out] xyz [arb.u.] Output rectangular equatorial 3-vector (δx, δy, δz), in the same units as the input. It may be the same vector as the input.

Returns

0 if successful, or else -1 if either vector argument is NULL (errno will be set to EINVAL).

Since

1.3

Author

Attila Kovacs

See also

novas_xyz_to_los()

novas_uvw_to_xyz()

Converts equatorial u,v,w projected (absolute or relative) coordinates to rectangular telescope x,y,z coordinates (in ITRS) to for a specified line of sight.

u,v,w are Cartesian coordinates (u,v) along the local equatorial R.A. and declination directions as seen from a direction on the sky (w). As such, they are effectively ITRS-based line-of-sight (LOS) coordinates.

x,y,z are Cartesian coordinates w.r.t the Greenwich meridian in the ITRS frame. The directions are x: long=0, lat=0; y: long=90, lat=0; z: lat=90.

Parameters

xyz [arb.u.] Absolute or relative u,v,w coordinates (double[3]). ha [h] Hourangle (LST - RA) i.e., the difference between the Local (apparent) Sidereal Time and the apparent (true-of-date) Right Ascension of observed source. dec [deg] Apparent (true-of-date) declination of source [out] uvw [arb.u.] Converted x,y,z coordinates (double[3]) in the same unit as uvw. It may be the same vector as the input.

Returns

0 if successful, or else -1 if either vector argument is NULL (errno will be set to EINVAL)

Since

1.3

Author

Attila Kovacs

See also

novas_xyz_to_uvw()

References novas_los_to_xyz().

Converts a 3D rectangular equatorial (δx, δy, δz) vector to a polar (δφ, δθ δr) vector along a line-of-sight.

Parameters

xyz [arb.u.] Rectangular equatorial 3-vector (δx, δy, δz). lon [deg] Line-of-sight longitude. lat [deg] Line-of-sight latitude. [out] los [arb.u.] Output line-of-sight 3-vector (δφ, δθ δr), in the same units as the input. It may be the same vector as the input.

Returns

0 if successful, or else -1 if either vector argument is NULL (errno will be set to EINVAL).

Since

1.3

Author

Attila Kovacs

See also

novas_los_to_xyz()

novas_xyz_to_uvw()

Converts rectangular telescope x,y,z (absolute or relative) coordinates (in ITRS) to equatorial u,v,w projected coordinates for a specified line of sight.

x,y,z are Cartesian coordinates w.r.t the Greenwich meridian, in the ITRS frame. The directions are x: long=0, lat=0; y: long=90, lat=0; z: lat=90.

u,v,w are Cartesian coordinates (u,v) along the local equatorial R.A. and declination directions as seen from a direction on the sky (w). As such, they are effectively ITRS-based line-of-sight (LOS) coordinates.

Parameters

xyz [arb.u.] Absolute or relative x,y,z coordinates (double[3]). ha [h] Hourangle (LST - RA) i.e., the difference between the Local (apparent) Sidereal Time and the apparent (true-of-date) Right Ascension of observed source. dec [deg] Apparent (true-of-date) declination of source [out] uvw [arb.u.] Converted u,v,w coordinates (double[3]) in same units as xyz. It may be the same vector as the input.

Returns

0 if successful, or else -1 if either vector argument is NULL (errno will be set to EINVAL)

Since

1.3

Author

Attila Kovacs

See also

novas_uvw_to_xyz()

References novas_xyz_to_los().

Calculates the positions and velocities for the Solar-system bodies, e.g. for use for graviational deflection calculations. The planet positions are calculated relative to the observer location, while velocities are w.r.t. the SSB. Both positions and velocities are antedated for light travel time, so they accurately reflect the apparent position (and barycentric motion) of the bodies from the observer's perspective.

Parameters

jd_tdb [day] Barycentric Dynamical Time (TDB) based Julian date accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1). In full accuracy mode, it will calculate the deflection due to the Sun, Jupiter, Saturn and Earth. In reduced accuracy mode, only the deflection due to the Sun is calculated. pos_obs [AU] Position 3-vector of observer (or the geocenter), with respect to origin at solar system barycenter, referred to ICRS axes, components in AU. pl_mask Bitwise (1 << planet-number) mask indicating which planets to request data for. See enum novas_planet for the enumeration of planet numbers. [out] planets Pointer to apparent planet data to populate. have positions and velocities calculated successfully. See enum novas_planet for the enumeration of planet numbers.

Returns

0 if successful, -1 if any of the pointer arguments is NULL or if the output vector is the same as pos_obs, or the error from ephemeris().

See also

enum novas_planet

grav_planets()

grav_undo_planets()

set_planet_provider()

set_planet_provider_hp()

Since

1.1

Author

Attila Kovacs

References light_time2(), make_planet(), novas_debug(), NOVAS_DEBUG_EXTRA, NOVAS_DEBUG_OFF, novas_get_debug_mode(), NOVAS_PLANETS, and NOVAS_SUN.

Calculates the ICRS position and velocity of the observer relative to the Solar System Barycenter (SSB).

Parameters

jd_tdb [day] Barycentric Dynamical Time (TDB) based Julian date. ut1_to_tt [s] TT - UT1 time difference. Used only when 'location->where' is NOVAS_OBSERVER_ON_EARTH (1) or NOVAS_OBSERVER_IN_EARTH_ORBIT (2). accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) obs The observer location, relative to which the output positions and velocities are to be calculated geo_pos [AU] ICRS position vector of the geocenter w.r.t. the Solar System Barycenter (SSB). If either geo_pos or geo_vel is NULL, it will be calculated when needed. geo_vel [AU/day] ICRS velocity vector of the geocenter w.r.t. the Solar System Barycenter (SSB). If either geo_pos or geo_vel is NULL, it will be calculated when needed. [out] pos [AU] Position 3-vector of the observer w.r.t. the Solar System Barycenter (SSB). It may be NULL if not required. [out] vel [AU/day] Velocity 3-vector of the observer w.r.t. the Solar System Barycenter (SSB). It must be distinct from the pos output vector, and may be NULL if not required.

Returns

0 if successful, or the error from geo_posvel(), or else -1 (with errno indicating the type of error).

Author

Attila Kovacs

Since

1.3

See also

place()

References ephemeris(), geo_posvel(), NOVAS_AIRBORNE_OBSERVER, NOVAS_BARYCENTER, NOVAS_EARTH_INIT, NOVAS_OBSERVER_IN_EARTH_ORBIT, NOVAS_OBSERVER_ON_EARTH, NOVAS_OBSERVER_PLACES, NOVAS_SOLAR_SYSTEM_OBSERVER, and tt2tdb().

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