Functions for computing transforms from image feature correspondences. More...
#include <cxcore.h>
Data Structures | |
struct | ransac_data |
holds feature data relevant to ransac More... | |
Defines | |
#define | RANSAC_INLIER_FRAC_EST 0.25 |
pessimistic estimate of fraction of inlers for RANSAC | |
#define | RANSAC_PROB_BAD_SUPP 0.10 |
estimate of the probability that a correspondence supports a bad model | |
Typedefs | |
typedef CvMat *(* | ransac_xform_fn )(CvPoint2D64f *pts, CvPoint2D64f *mpts, int n) |
Prototype for transformation functions passed to ransac_xform(). | |
typedef double(* | ransac_err_fn )(CvPoint2D64f pt, CvPoint2D64f mpt, CvMat *T) |
Prototype for error functions passed to ransac_xform(). | |
Functions | |
CvMat * | ransac_xform (struct feature *features, int n, int mtype, ransac_xform_fn xform_fn, int m, double p_badxform, ransac_err_fn err_fn, double err_tol, struct feature ***inliers, int *n_in) |
Calculates a best-fit image transform from image feature correspondences using RANSAC. | |
CvMat * | dlt_homog (CvPoint2D64f *pts, CvPoint2D64f *mpts, int n) |
Calculates a planar homography from point correspondeces using the direct linear transform. | |
CvMat * | lsq_homog (CvPoint2D64f *pts, CvPoint2D64f *mpts, int n) |
Calculates a least-squares planar homography from point correspondeces. | |
double | homog_xfer_err (CvPoint2D64f pt, CvPoint2D64f mpt, CvMat *H) |
Calculates the transfer error between a point and its correspondence for a given homography, i.e. | |
CvPoint2D64f | persp_xform_pt (CvPoint2D64f pt, CvMat *T) |
Performs a perspective transformation on a single point. |
Functions for computing transforms from image feature correspondences.
Copyright (C) 2006-2010 Rob Hess <hess@eecs.oregonstate.edu>
typedef CvMat*(* ransac_xform_fn)(CvPoint2D64f *pts, CvPoint2D64f *mpts, int n) |
Prototype for transformation functions passed to ransac_xform().
Functions of this type should compute a transformation matrix given a set of point correspondences.
pts | array of points | |
mpts | array of corresponding points; each pts[i], i=0..n-1, corresponds to mpts[i] | |
n | number of points in both pts and mpts |
typedef double(* ransac_err_fn)(CvPoint2D64f pt, CvPoint2D64f mpt, CvMat *T) |
Prototype for error functions passed to ransac_xform().
For a given point, its correspondence, and a transform, functions of this type should compute a measure of error between the correspondence and the point after the point has been transformed by the transform.
pt | a point | |
mpt | pt's correspondence | |
T | a transform |
CvMat* ransac_xform | ( | struct feature * | features, | |
int | n, | |||
int | mtype, | |||
ransac_xform_fn | xform_fn, | |||
int | m, | |||
double | p_badxform, | |||
ransac_err_fn | err_fn, | |||
double | err_tol, | |||
struct feature *** | inliers, | |||
int * | n_in | |||
) |
Calculates a best-fit image transform from image feature correspondences using RANSAC.
For more information refer to:
Fischler, M. A. and Bolles, R. C. Random sample consensus: a paradigm for model fitting with applications to image analysis and automated cartography. Communications of the ACM, 24, 6 (1981), pp. 381--395.
features | an array of features; only features with a non-NULL match of type mtype are used in homography computation | |
n | number of features in feat | |
mtype | determines which of each feature's match fields to use for transform computation; should be one of FEATURE_FWD_MATCH, FEATURE_BCK_MATCH, or FEATURE_MDL_MATCH; if this is FEATURE_MDL_MATCH, correspondences are assumed to be between a feature's img_pt field and its match's mdl_pt field, otherwise correspondences are assumed to be between the the feature's img_pt field and its match's img_pt field | |
xform_fn | pointer to the function used to compute the desired transformation from feature correspondences | |
m | minimum number of correspondences necessary to instantiate the transform computed by xform_fn | |
p_badxform | desired probability that the final transformation returned by RANSAC is corrupted by outliers (i.e. the probability that no samples of all inliers were drawn) | |
err_fn | pointer to the function used to compute a measure of error between putative correspondences and for a given transform | |
err_tol | correspondences within this distance of each other are considered as inliers for a given transform | |
inliers | if not NULL, output as an array of pointers to the final set of inliers; memory for this array is allocated by this function and must be freed by the caller using free(*inliers) | |
n_in | if not NULL, output as the final number of inliers |
CvMat* dlt_homog | ( | CvPoint2D64f * | pts, | |
CvPoint2D64f * | mpts, | |||
int | n | |||
) |
Calculates a planar homography from point correspondeces using the direct linear transform.
Intended for use as a ransac_xform_fn.
pts | array of points | |
mpts | array of corresponding points; each pts[i], i=0..n-1, corresponds to mpts[i] | |
n | number of points in both pts and mpts; must be at least 4 |
CvMat* lsq_homog | ( | CvPoint2D64f * | pts, | |
CvPoint2D64f * | mpts, | |||
int | n | |||
) |
Calculates a least-squares planar homography from point correspondeces.
Intended for use as a ransac_xform_fn.
pts | array of points | |
mpts | array of corresponding points; each pts[i], i=0..n-1, corresponds to mpts[i] | |
n | number of points in both pts and mpts; must be at least 4 |
double homog_xfer_err | ( | CvPoint2D64f | pt, | |
CvPoint2D64f | mpt, | |||
CvMat * | H | |||
) |
Calculates the transfer error between a point and its correspondence for a given homography, i.e.
for a point , it's correspondence
, and homography
, computes
. Intended for use as a ransac_err_fn.
pt | a point | |
mpt | pt's correspondence | |
H | a homography matrix |
CvPoint2D64f persp_xform_pt | ( | CvPoint2D64f | pt, | |
CvMat * | T | |||
) |
Performs a perspective transformation on a single point.
That is, for a point and a
matrix
this function returns the point
, where
,
and
.
Note that affine transforms are a subset of perspective transforms.
pt | a 2D point | |
T | a perspective transformation matrix |