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1 function [is,S] = isintpl(x1,y1,x2,y2)
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2 % ISINTPL Check for intersection of polygons.
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3 % [IS,S] = ISINTPL(X1,Y1,X2,Y2) Accepts coordinates
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4 % X1,Y1 and X2, Y2 of two polygons. Returns scalar
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5 % IS equal to 1 if these polygons intersect each other
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6 % and 0 if they do not.
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7 % Also returns Boolean matrix S of the size length(X1)
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8 % by length(X2) so that {ij} element of which is 1 if
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9 % line segments i to i+1 of the first polygon and
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10 % j to j+1 of the second polygon intersect each other,
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11 % 0 if they don't and .5 if they "touch" each other.
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12
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13 % Copyright (c) 1995 by Kirill K. Pankratov,
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14 % kirill@plume.mit.edu.
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15 % 06/20/95, 08/25/95
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16
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17
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18 % Handle input ...................................
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19 if nargin==0, help isintpl, return, end
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20 if nargin<4
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21 error(' Not enough input arguments ')
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22 end
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23
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24 % Make column vectors and check sizes ............
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25 x1 = x1(:); y1 = y1(:);
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26 x2 = x2(:); y2 = y2(:);
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27 l1 = length(x1);
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28 l2 = length(x2);
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29 if length(y1)~=l1 | length(y2)~=l2
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30 error('(X1,Y1) and (X2,Y2) must pair-wise have the same length.')
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31 end
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32
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33 % Quick exit if empty
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34 if l1<1 | l2<1, is = []; S = []; return, end
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35
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36 % Check if their ranges are intersecting .........
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37 lim1 = [min(x1) max(x1)]';
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38 lim2 = [min(x2) max(x2)]';
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39 isx = interval(lim1,lim2); % X-ranges
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40 lim1 = [min(y1) max(y1)]';
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41 lim2 = [min(y2) max(y2)]';
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42 isy = interval(lim1,lim2); % Y-ranges
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43 is = isx & isy;
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44 S = zeros(l2,l1);
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45
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46 if ~is, return, end % Early exit if disparate limits
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47
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48 % Indexing .......................................
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49 [i11,i12] = meshgrid(1:l1,1:l2);
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50 [i21,i22] = meshgrid([2:l1 1],[2:l2 1]);
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51 i11 = i11(:); i12 = i12(:);
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52 i21 = i21(:); i22 = i22(:);
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53
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54 % Calculate matrix of intersections ..............
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55 S(:) = iscross([x1(i11) x1(i21)]',[y1(i11) y1(i21)]',...
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56 [x2(i12) x2(i22)]',[y2(i12) y2(i22)]')';
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57
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58 S = S';
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59 is = any(any(S));
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60
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