int chirp_metric(double x, double y, double *m);This routine computes the coefficients of a local distance metric on the space of chirp templates, at a specified location in that space. It returns 0 upon successful completion, or 1 if the metric could not be computed at that point.
The arguments are:
Note that this routine uses the global parameter global_space,
defined at the top of the
chirp_templates.c module. This parameter must be set by the routines set_chirp_space() or get_chirp_templates() before chirp_metric() can be called. The coordinate system used is the one defined in the global_space structure: it is to a (counterclockwise) rotation of the coordinate system by an angle of global_space.angle. The metric is computed by interpolating the grid of precomputed quadratic coefficients of the match function, stored in global_space.grid.
The local distance function is defined so that the match decreases to
the value global_space.match at a proper distance of 1. That
is, the unit of proper distance is defined to be the maximum template
patch radius. The metric coefficients m[0..2] are related to
the proper interval by:
This routine also checks to make sure that the resulting metric is positive definite, which should always be the case if the match function is locally paraboloidal (rather than a saddle).