Homography Matrix

44 Ansichten (letzte 30 Tage)
Tejas Kulkarni
Tejas Kulkarni am 15 Jan. 2012
Bearbeitet: Matt J am 26 Apr. 2022
Can somebody please help me in understanding how to calculate an homography matrix in matlab.
  1 Kommentar
Lalit Patil
Lalit Patil am 22 Jan. 2013
I am finding homography matrix in another way and it is 3*3
So, i want to know that in image where to apply or what to do of this homography matrix.?
Why we are finding this matrix..?

Melden Sie sich an, um zu kommentieren.

Antworten (2)

David Young
David Young am 15 Jan. 2012
You don't say what you are starting from. If you have a set of matched input and output points, one possible method is given here. A simple implementation is below.
function v = homography_solve(pin, pout)
% HOMOGRAPHY_SOLVE finds a homography from point pairs
% V = HOMOGRAPHY_SOLVE(PIN, POUT) takes a 2xN matrix of input vectors and
% a 2xN matrix of output vectors, and returns the homogeneous
% transformation matrix that maps the inputs to the outputs, to some
% approximation if there is noise.
%
% This uses the SVD method of
% http://www.robots.ox.ac.uk/%7Evgg/presentations/bmvc97/criminispaper/node3.html
% David Young, University of Sussex, February 2008
if ~isequal(size(pin), size(pout))
error('Points matrices different sizes');
end
if size(pin, 1) ~= 2
error('Points matrices must have two rows');
end
n = size(pin, 2);
if n < 4
error('Need at least 4 matching points');
end
% Solve equations using SVD
x = pout(1, :); y = pout(2,:); X = pin(1,:); Y = pin(2,:);
rows0 = zeros(3, n);
rowsXY = -[X; Y; ones(1,n)];
hx = [rowsXY; rows0; x.*X; x.*Y; x];
hy = [rows0; rowsXY; y.*X; y.*Y; y];
h = [hx hy];
if n == 4
[U, ~, ~] = svd(h);
else
[U, ~, ~] = svd(h, 'econ');
end
v = (reshape(U(:,9), 3, 3)).';
end
If your initial data is in some other form, such as camera position parameters relative to the plane, please say.
EDIT - added:
To apply the resulting matrix to a set of points, you can use the following function.
function y = homography_transform(x, v)
% HOMOGRAPHY_TRANSFORM applies homographic transform to vectors
% Y = HOMOGRAPHY_TRANSFORM(X, V) takes a 2xN matrix, each column of which
% gives the position of a point in a plane. It returns a 2xN matrix whose
% columns are the input vectors transformed according to the homography
% V, represented as a 3x3 homogeneous matrix.
q = v * [x; ones(1, size(x,2))];
p = q(3,:);
y = [q(1,:)./p; q(2,:)./p];
end
  13 Kommentare
Wei Han
Wei Han am 25 Mär. 2022
Bearbeitet: Wei Han am 25 Mär. 2022
Hi, I just want to thank for your code, it's really helped me!
Sahana Srivathsa
Sahana Srivathsa am 25 Apr. 2022
This is very helpful. I think equation for q needs to be slightly altered.
q = v * [x; y; ones(1, size(x,2))];

Melden Sie sich an, um zu kommentieren.


Matt J
Matt J am 25 Apr. 2022
Bearbeitet: Matt J am 25 Apr. 2022
  1 Kommentar
Matt J
Matt J am 26 Apr. 2022
Bearbeitet: Matt J am 26 Apr. 2022
You shouldn't be extracting the matrix. You should be using tform.transformPointsForward().

Melden Sie sich an, um zu kommentieren.

Kategorien

Mehr zu Sparse Matrices finden Sie in Help Center und File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by