imgfeatures.h

/**@file
   Functions and structures for dealing with image features
   
   @author Rob Hess
   @version 1.0.0-20060607
*/

#ifndef IMGFEATURES_H
#define IMGFEATURES_H

#include "cxcore.h"

/** FEATURE_OXFD <BR> FEATURE_LOWE */
enum feature_type
  {
    FEATURE_OXFD,
    FEATURE_LOWE,
  };

/** FEATURE_FWD_MATCH <BR> FEATURE_BCK_MATCH <BR> FEATURE_MDL_MATCH */
enum feature_match_type
  {
    FEATURE_FWD_MATCH,
    FEATURE_BCK_MATCH,
    FEATURE_MDL_MATCH,
  };


/* colors in which to display different feature types */
#define FEATURE_OXFD_COLOR CV_RGB(255,255,0)
#define FEATURE_LOWE_COLOR CV_RGB(255,0,255)

/** max feature descriptor length */
#define FEATURE_MAX_D 128


/**
   Structure to represent an affine invariant image feature.  The fields
   x, y, a, b, c represent the affine region around the feature:

   a(x-u)(x-u) + 2b(x-u)(y-v) + c(y-v)(y-v) = 1
*/
struct feature
{
  double x;                      /**< x coord */
  double y;                      /**< y coord */
  double a;                      /**< affine region parameter */
  double b;                      /**< affine region parameter */
  double c;                      /**< affine region parameter */
  double scl;                    /**< scale of a Lowe-style feature */
  double ori;                    /**< orientation of a Lowe-style feature */
  int d;                         /**< descriptor length */
  double descr[FEATURE_MAX_D];   /**< descriptor */
  int type;                      /**< feature type, OXFD or LOWE */
  int class;                     /**< all-purpose feature class */
  struct feature* fwd_match;     /**< matching feature from forward image */
  struct feature* bck_match;     /**< matching feature from backmward image */
  struct feature* mdl_match;     /**< matching feature from model */
  CvPoint2D64f img_pt;           /**< location in image */
  CvPoint2D64f mdl_pt;           /**< location in model */
  void* feature_data;            /**< user-definable data */
};

/**
   Displays a set of features on an image

   @param img image on which to display features
   @param feat array of Oxford-type features
   @param n number of features
*/
extern void draw_features( IplImage* img, struct feature* feat, int n );


/**
   Calculates the squared Euclidian distance between two feature descriptors.
   
   @param f1 first feature
   @param f2 second feature

   @return Returns the squared Euclidian distance between the descriptors of
     \a f1 and \a f2.
*/
extern double descr_dist_sq( struct feature* f1, struct feature* f2 );


#endif