topocentric coordinates(top-ŏ-sen -trik) The coordinates of a celestial body measured from the surface of the Earth. For a star there is little or no detectable difference between topocentric coordinates and those referring to the Earth's center in a geocentric coordinate system. For a member of the Solar System the difference can be significant and a correction must be made.
three quantities that specify the spatial position of an observed point or object, such as a satellite or an aircraft, in a coordinate system whose origin coincides with the point of observation on the earth’s surface. Topocentric coordinates are used for analyzing the results of observations in astronomy, astrometry, geodesy, and satellite geodesy. Depending on the choice of the coordinate reference plane, topocentric coordinates may be equatorial, horizontal, or orbital.