imgfeatures.h

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2018, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */

#ifndef IMGFEATURES_H
#define IMGFEATURES_H

//#include "cxcore.h"
// Universal include for all versions of OpenCV
#include <mrpt/otherlibs/do_opencv_includes.h>

#ifdef __cplusplus
extern "C" {
#endif

/** 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; /**< Oxford-type affine region parameter */
    double b; /**< Oxford-type affine region parameter */
    double c; /**< Oxford-type 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 category; /**< all-purpose feature category */
    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 */
};

/**
Reads image features from file.  The file should be formatted as from
the code provided by the Visual Geometry Group at Oxford or from the
code provided by David Lowe.


@param filename location of a file containing image features
@param type determines how features are input.  If \a type is FEATURE_OXFD,
    the input file is treated as if it is from the code provided by the VGG
    at Oxford: http://www.robots.ox.ac.uk:5000/~vgg/research/affine/index.html
    <BR><BR>
    If \a type is FEATURE_LOWE, the input file is treated as if it is from
    David Lowe's SIFT code: http://www.cs.ubc.ca/~lowe/keypoints
@param feat pointer to an array in which to store imported features

@return Returns the number of features imported from filename or -1 on error
*/
extern int import_features(char* filename, int type, struct feature** feat);

/**
Exports a feature set to a file formatted depending on the type of
features, as specified in the feature struct's type field.

@param filename name of file to which to export features
@param feat feature array
@param n number of features

@return Returns 0 on success or 1 on error
*/
extern int export_features(char* filename, struct feature* feat, int n);

/**
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);

#ifdef __cplusplus
}
#endif

#endif