In SPICE terminology, a "coordinate system" is a mathematical means of naming vectors or points in a specified reference frame. Examples are "Cartesian coordinates" or "spherical coordinates." The coordinate systems supported by webGeocalc are:

Rectangular (also called “Cartesian”):

Coordinates are X, Y, Z. X, Y, Z are, respectively, the components of the point (or vector head, with the vector tail at the origin) along the X, Y, and Z axes of a specified reference frame. Units are km.

Right ascension/declination (also called “RA/Dec”):

webGeocalc supports computation of RA/Dec relative to any specified reference frame (not just earth-centered inertial frames). Coordinates are range, right ascension (“RA”), and declination (“Dec”). range is the distance of the point (vector head) from the origin (vector tail). The units associated with `range' are km. ra is the right ascension of the point. This is the angular distance measured toward the east from the prime meridian to the meridian containing the point. The direction of increasing right ascension is from the +X axis of a specified reference frame towards the +Y axis. The range of `ra' is [0, 360] degrees. dec is the declination of the point. This is the angle from the XY plane of the ray from the origin through the point. The range of `dec' is [-90, 90] degrees.

Planetocentric (also called “latitudinal”):

Coordinates are radius, longitude, and latitude. radius Distance of the point (vector head) from the origin (vector tail). The units associated with `radius' are km. longitude Longitude of the point. This is angle between the prime meridian and the meridian containing the input point. The direction of increasing longitude is from the +X axis towards the +Y axis. The range of `longitude' is [-180, 180] degrees. latitude Latitude of the point. This is the angle from the XY plane of the ray from the origin through the point. The range of `latitude' is [-90, 90] degrees.

Cylindrical:

Coordinates are radius, longitude, and Z. radius Distance of the point of interest (vector head, with the vector tail at the origin) from the Z axis. longitude This is angle between the prime meridian and the meridian containing the point. The range of longitude is [0, 360] degrees. Z Height of the point above the XY plane. Units are km.

Spherical:

Coordinates are radius, colatitude, and longitude. radius Distance of the point (vector head) from the origin (vector tail). Units are km. colatitude Angle between the point and the positive Z-axis. longitude Longitude of the point in radians. This is angle between the prime meridian and the meridian containing the input point. Longitude increases in the counterclockwise sense about the positive Z-axis. The range of longitude is [-180, 180] degrees.

Planetodetic (also called “Geodetic”):

Planetodetic coordinates are applicable only to bodies that have a reference spheroid. Coordinates are longitude, latitude, and altitude. longitude Planetodetic longitude of the point (or vector head, with the vector tail at the origin). This is the angle between the prime meridian and the meridian containing the point. The direction of increasing longitude is from the +X axis towards the +Y axis. The range of `longitude' is [-180, 180] degrees. latitude Planetoetic latitude of the point. For a point P on the reference spheroid, this is the angle between the XY plane and the outward normal vector at P. For a point P not on the reference spheroid, the geodetic latitude is that of the closest point to P on the spheroid. The range of `latitude' is [-90, 90] degrees. altitude Altitude of point above the reference spheroid. Units are km.

Planetographic:

Planetographic coordinates are applicable only to bodies that have a reference spheroid and a spin direction. Coordinates are longitude, latitude, and altitude. longitude Planetographic longitude of the point (or vector head, with the vector tail at the origin). This is the angle between the prime meridian and the meridian containing the point. For bodies having prograde (aka direct) rotation, the direction of increasing longitude is positive west: from the +X axis of the specified reference frame toward the -Y axis. For bodies having retrograde rotation, the direction of increasing longitude is positive east: from the +X axis toward the +Y axis. The earth, moon, and sun are exceptions: planetographic longitude is measured positive east for these bodies. The default sense of planetographic longitude for a given body may be overridden via text kernel assignments. See the header of the SPICE routine RECPGR for details. The range of `longitude' is [0, 360] degrees. latitude Planetographic latitude of the point. For a point P on the reference spheroid, this is the angle between the XY plane and the outward normal vector at P. For a point P not on the reference spheroid, the planetographic latitude is that of the closest point to P on the spheroid. The range of `latitude' is [-90, 90] degrees. altitude Altitude of point above the reference spheroid.