This function finds the distance between two points whose Frame coordinates are given. The distance calculated is that along the geodesic curve that joins the two points.

For example, in a basic Frame, the distance calculated will be the Cartesian distance along the straight line joining the two points. For a more specialised Frame describing a sky coordinate system, however, it would be the distance along the great circle passing through two sky positions.

RESULT = AST_DISTANCE( THIS, POINT1, POINT2, STATUS )

THIS = INTEGER (Given)

POINT1( $\ast$ ) = DOUBLE PRECISION (Given)

POINT2( $\ast$ ) = DOUBLE PRECISION (Given)

STATUS = INTEGER (Given and Returned)

AST_DISTANCE = DOUBLE PRECISION

• This function will return a " bad" result value (AST__BAD) if any of the input coordinates has this value.

• A " bad" value will also be returned if this function is invoked with STATUS set to an error value, or if it should fail for any reason.