%?HOMOGRAPHY2D?-?computes?2D?homography
%
%?Usage:???H?=?homography2d（x1?x2）
%??????????H?=?homography2d（x）
%
%?Arguments:
%??????????x1??-?3xN?set?of?homogeneous?points
%??????????x2??-?3xN?set?of?homogeneous?points?such?that?x1<->x2
%?????????
%???????????x??-?If?a?single?argument?is?supplied?it?is?assumed?that?it
%????????????????is?in?the?form?x?=?[x1;?x2]
%?Returns:
%??????????H?-?the?3x3?homography?such?that?x2?=?H*x1
%
%?This?code?follows?the?normalised?direct?linear?transformation?
%?algorithm?given?by?Hartley?and?Zisserman?“Multiple?View?Geometry?in
%?Computer?Vision“?p92.
%

%?Peter?Kovesi
%?School?of?Computer?Science?&?Software?Engineering
%?The?University?of?Western?Australia
%?pk?at?csse?uwa?edu?au
%?http://www.csse.uwa.edu.au/~pk
%
%?May?2003??-?Original?version.
%?Feb?2004??-?Single?argument?allowed?for?to?enable?use?with?RANSAC.
%?Feb?2005??-?SVD?changed?to?‘Economy‘?decomposition?（thanks?to?Paul?O‘Leary）

function?H?=?homography2d（varargin）
????
????[x1?x2]?=?checkargs（varargin（:））;

????%?Attempt?to?normalise?each?set?of?points?so?that?the?origin?
????%?is?at?centroid?and?mean?distance?from?origin?is?sqrt（2）.
????[x1?T1]?=?normalise2dpts（x1）;
????[x2?T2]?=?normalise2dpt