User Documentation
RAVL, Recognition And Vision Library
Ravl - Introduction - Coordinate Systems

2D Coordinate Systems in RAVL

In 2D RAVL objects, such as arrays, matrices and images, the indices are in the order: row, column (as in conventional matrix notation). In pairs of reals (e.g. 2D vectors and points), the components are in the order x, y. Normally these two categories of objects do not interact. However, when they do (e.g. if we want to construct a pixel position, an Index2dC from a Point2dC), the RAVL convention is this:

  • The row index is associated with the x value
  • The column index is associated with the y value

The implication is that RAVL adopts a 2D coordinate system in which the x coordinate points downwards, and the y coordinate to the right. Not what you were expecting? It has the advantages that:

  • the coordinate system is anti-clockwise, as is conventional in mathematics
  • the first array coordinate is associated with the first vector component etc.

Documentation by CxxDoc: Tue Aug 13 10:00:52 2002