next up previous 264
Next: AST_DOWNSIZE - Reduce the number of vertices in a Polygon
Up: AST Routine Descriptions
Previous: AST_DELFITS - Delete the current FITS card in a FitsChan


AST_DISTANCE - Calculate the distance between two points in a Frame

Description:
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.

Invocation:
RESULT = AST_DISTANCE( THIS, POINT1, POINT2, STATUS )
Arguments:
THIS = INTEGER (Given)
Pointer to the Frame.
POINT1( $*$ ) = DOUBLE PRECISION (Given)
An array with one element for each Frame axis (Naxes attribute) containing the coordinates of the first point.
POINT2( $*$ ) = DOUBLE PRECISION (Given)
An array with one element for each Frame axis containing the coordinates of the second point.
STATUS = INTEGER (Given and Returned)
The global status.
Returned Value:
AST_DISTANCE = DOUBLE PRECISION
The distance between the two points.
Notes:
  • 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.


next up previous 264
Next: AST_DOWNSIZE - Reduce the number of vertices in a Polygon
Up: AST Routine Descriptions
Previous: AST_DELFITS - Delete the current FITS card in a FitsChan

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council