www.pudn.com > geometric.rar > within.m, change:2004-08-13,size:3950b


function result=within(xpt,ypt,xpoly,ypoly) 
 
% result = within(xpt,ypt,xpoly,ypoly) 
% 
% function returns 1 if (xpt,ypt) is inside the polygon described by 
% xpoly and ypoly and 0 otherwise 
% 
%  xpt = x coordinates of the test points. May be a scalar, vector or matrix. 
%  ypt = y coordinates of the test pts 
%  xpoly = vector of the x coordinates of the polygon vertices 
%          The last vertex is tested against the first and is discarded 
%          if it is identical 
% ypoly =  vector of the y coordinates of the polygon vertices 
% 
% result =  vector of boolean values the same size as xpt(:). Points inside 
%           the polygon may be addressed as xpt(result) and ypt(result) while 
%           those outside are xpt(~result) and ypt(~result) 
% 
%  Transcribed from FORTAN by G.F. Margrave, October 1993 
%  FORTRAN written by T.N. Bishop, May 1989 
%  Algorithm after B.J. Larkin, Computer & Geosciences, Vol 14, pp1-14, 1988 
%  Original algorithm due to K.R. Anderson, Mathematical Geology, Vol 8, no 1, 
%  1976, pp 105-106 
% 
% NOTE: It is illegal for you to use this software for a purpose other 
% than non-profit education or research UNLESS you are employed by a CREWES 
% Project sponsor. By using this software, you are agreeing to the terms 
% detailed in this software's Matlab source file. 
  
% BEGIN TERMS OF USE LICENSE 
% 
% This SOFTWARE is maintained by the CREWES Project at the Department 
% of Geology and Geophysics of the University of Calgary, Calgary, 
% Alberta, Canada.  The copyright and ownership is jointly held by  
% its author (identified above) and the CREWES Project.  The CREWES  
% project may be contacted via email at:  crewesinfo@crewes.org 
%  
% The term 'SOFTWARE' refers to the Matlab source code, translations to 
% any other computer language, or object code 
% 
% Terms of use of this SOFTWARE 
% 
% 1) Use of this SOFTWARE by any for-profit commercial organization is 
%    expressly forbidden unless said organization is a CREWES Project 
%    Sponsor. 
% 
% 2) A CREWES Project sponsor may use this SOFTWARE under the terms of the  
%    CREWES Project Sponsorship agreement. 
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%    use this SOFTWARE subject to the following terms and conditions: 
%    - this SOFTWARE is for teaching or research purposes only. 
%    - this SOFTWARE may be distributed to other students or researchers  
%      provided that these license terms are included. 
%    - reselling the SOFTWARE, or including it or any portion of it, in any 
%      software that will be resold is expressly forbidden. 
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% END TERMS OF USE LICENSE 
 
 
	[m,n]=size(xpoly); 
	if( m~= 1) xpoly = xpoly'; end % make sure we have row vectors 
	[m,n]=size(ypoly); 
	if( m~= 1) ypoly = ypoly'; end % make sure we have row vectors 
 
% determine the number of vertices 
 
	nvert = length(xpoly); 
	if( nvert ~= length(ypoly) ) 
		error( 'xpoly and ypoly must be the same length' ); 
	end 
 
% check for last pt == first pt 
	if( (xpoly(1)==xpoly(nvert))&(ypoly(1)==ypoly(nvert))) 
		xpoly = xpoly(1:nvert-1); 
		ypoly = ypoly(1:nvert-1); 
		nvert=nvert-1; 
	end  
 
	if( nvert < 3 ) 
		error( 'polygon must have more than 2 vertices'); 
	end 
 
	 
% count number of polygon sides to the right of the point 
 
	xprev = [xpoly(nvert) xpoly(1:nvert-1)]; 
	yprev = [ypoly(nvert) ypoly(1:nvert-1)]; 
 
	xpt=xpt(:);ypt=ypt(:); 
	result=zeros(size(xpt)); % guilty until proven innocent 
	 
	for n=1:length(result) 
 
	for k=1:nvert 
		test1 = ypt(n) > yprev(k); 
		test2 = ypt(n) <= ypoly(k); 
		if( test1 == test2 ) 
			grad = (xpoly(k)-xprev(k))/(ypoly(k)-yprev(k)); 
			xint = xprev(k) - grad*yprev(k); 
			xcut = grad*ypt(n)+xint; 
			if( xpt(n) < xcut ) result(n) = ~result(n); end 
		end 
	end 
 
	end