#include <mrpt/otherlibs/do_opencv_includes.h>

Include dependency graph for xform.h:

Classes
struct	ransac_data
	holds feature data relevant to ransac More...

Macros
#define	RANSAC_ERR_TOL 3

#define	RANSAC_INLIER_FRAC_EST 0.25
	pessimistic estimate of fraction of inlers for RANSAC More...

#define	RANSAC_PROB_BAD_SUPP 0.10
	estimate of the probability that a correspondence supports a bad model More...

#define	feat_ransac_data(feat) ( (struct ransac_data*) (feat)->feature_data )

Typedefs
typedef CvMat (	ransac_xform_fn) (CvPoint2D64f pts, CvPoint2D64f mpts, int n)
	Prototype for transformation functions passed to ransac_xform(). More...

typedef double(*	ransac_err_fn) (CvPoint2D64f pt, CvPoint2D64f mpt, CvMat *M)
	Prototype for error functions passed to ransac_xform(). More...

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. More...

CvMat *	lsq_homog (CvPoint2D64f pts, CvPoint2D64f mpts, int n)
	Calculates a least-squares planar homography from point correspondeces. More...

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. More...

CvPoint2D64f	persp_xform_pt (CvPoint2D64f pt, CvMat *T)
	Performs a perspective transformation on a single point. More...

Macro Definition Documentation

◆ feat_ransac_data

#define feat_ransac_data ( feat ) ( (struct ransac_data*) (feat)->feature_data )

Definition at line 41 of file xform.h.

◆ RANSAC_ERR_TOL

#define RANSAC_ERR_TOL 3

Definition at line 32 of file xform.h.

◆ RANSAC_INLIER_FRAC_EST

#define RANSAC_INLIER_FRAC_EST 0.25

pessimistic estimate of fraction of inlers for RANSAC

Definition at line 35 of file xform.h.

◆ RANSAC_PROB_BAD_SUPP

#define RANSAC_PROB_BAD_SUPP 0.10

estimate of the probability that a correspondence supports a bad model

Definition at line 38 of file xform.h.

Typedef Documentation

◆ ransac_err_fn

typedef double(* ransac_err_fn) (CvPoint2D64f pt, CvPoint2D64f mpt, CvMat *M)

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.

Parameters

pt	a point
mpt	pt's correspondence
T	a transform

Returns: Should return a measure of error between mpt and pt after pt has been transformed by the transform T.

Definition at line 74 of file xform.h.

◆ ransac_xform_fn

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.

Parameters

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

Returns: Should return a transformation matrix that transforms each point in pts to the corresponding point in mpts or NULL on failure.

Definition at line 57 of file xform.h.

Function Documentation

◆ homog_xfer_err()

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 $x$ , it's correspondence $x'$ , and homography $H$ , computes $d(x', Hx)^2$ . Intended for use as a ransac_err_fn.

Parameters

pt	a point
mpt	pt's correspondence
H	a homography matrix

Returns: Returns the transfer error between pt and mpt given H

◆ lsq_homog()

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.

Parameters

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

Returns: Returns the $3 \times 3$ least-squares planar homography matrix that transforms points in pts to their corresponding points in mpts or NULL if fewer than 4 correspondences were provided

◆ persp_xform_pt()

CvPoint2D64f persp_xform_pt	(	CvPoint2D64f	pt,
		CvMat *	T
	)

Performs a perspective transformation on a single point.

That is, for a point $(x, y)$ and a $3 \times 3$ matrix $T$ this function returns the point $(u, v)$ , where

$[x' \ y' \ w']^T = T \times [x \ y \ 1]^T$ ,

and

$(u, v) = (x'/w', y'/w')$ .

Note that affine transforms are a subset of perspective transforms.

Parameters

pt	a 2D point
T	a perspective transformation matrix

Returns: Returns the point as above.

◆ ransac_xform()

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.

Parameters

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 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
n_in	if not NULL, output as the final number of inliers

Returns: Returns a transformation matrix computed using RANSAC or NULL on error or if an acceptable transform could not be computed.

Classes

Macros

Typedefs

Functions

Macro Definition Documentation

◆ feat_ransac_data

◆ RANSAC_ERR_TOL

◆ RANSAC_INLIER_FRAC_EST

◆ RANSAC_PROB_BAD_SUPP

Typedef Documentation

◆ ransac_err_fn

◆ ransac_xform_fn

Function Documentation

◆ homog_xfer_err()

◆ lsq_homog()

◆ persp_xform_pt()

◆ ransac_xform()