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/* RCSid $Id: interp2d.h,v 2.3 2013/02/09 20:56:40 greg Exp $ */
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/*
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* Header for interpolation of anisotropic samples on 2-D plane.
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*
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* G.Ward Feb 2013
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*/
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#ifndef _RAD_INTERP2D_H_
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#define _RAD_INTERP2D_H_
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#ifdef __cplusplus
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extern "C" {
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#endif
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#define NI2DSMF 0.42f /* minimal smoothing factor */
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#define NI2DIR (2*4) /* # interpolation directions */
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/* Data structure for interpolant */
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typedef struct {
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int ns; /* number of sample positions */
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float dmin; /* minimum diameter (default=1) */
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float smf; /* smoothing factor (def=NI2DSMF) */
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unsigned short (*da)[NI2DIR]; /* anisotropic distances (private) */
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float spt[1][2]; /* sample positions (extends struct) */
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} INTERP2;
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/* Allocate a new set of interpolation samples (caller assigns spt[] array) */
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extern INTERP2 *interp2_alloc(int nsamps);
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/* Resize interpolation array (caller must assign any new values) */
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extern INTERP2 *interp2_realloc(INTERP2 *ip, int nsamps);
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/* Assign full set of normalized weights to interpolate the given location */
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extern int interp2_weights(float wtv[], INTERP2 *ip, double x, double y);
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/* Get normalized weights and indexes for n best samples in descending order */
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extern int interp2_topsamp(float wt[], int si[], const int n,
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INTERP2 *ip, double x, double y);
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/* Free interpolant */
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extern void interp2_free(INTERP2 *ip);
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/* (Re)compute anisotropic basis function interpolant (normally automatic) */
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extern int interp2_analyze(INTERP2 *ip);
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/***************************************************************
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* Typical use is to allocate an INTERP2 struct and assign the
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* spt[] array with the ordered sample locations in x & y. (The
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* actual orientation of the axes is not important so long as
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* the application is consistent.) During interpolation, either
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* interp2_weights() is called to obtain a normalized weighting
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* vector for all the samples, or interp2_topsamp() is called to
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* get the most important N samples for the specified location.
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* The weights (and indexes in the case of interp2_topsamp)
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* are then used as coefficients for corresponding sample values
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* in a vector sum together that interpolates the function at that
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* location. Between the initial allocation call and the first
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* weight evaluation, the dmin member may be adjusted to
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* the distance under which samples will start to merge. If this
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* parameter is later changed, interp2_analyze() should be called
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* to recompute the interpolant.
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* The smf member sets the smoothing factor for interpolation.
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* The default setting of NI2DSMF produces near-optimal
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* interpolation when well-separated sample values are known
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* precisely. If a greater degree of mixing is desired, this
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* paremter may be increased and it will affect the next call
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* to interp2_weights() or interp2_topsamp().
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**************************************************************/
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#ifdef __cplusplus
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}
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#endif
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#endif /* !_RAD_INTERP2D_H_ */
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