clipPolyline

CLIPPOLYLINE Clip an open polyline with a rectangular box.

   POLY2 = clipPolyline(POLY, BOX);
   POLY is N-by-2 array of vertex coordinates.
   BOX has the form: [XMIN XMAX YMIN YMAX].
   Returns the set of polylines created by the intersection of the
   polyline POLY and the bounding box BOX. The result is a cell array with
   as many cells as the number of curve clips.


   Example
     circle = [5 5 6];
     poly = circleToPolygon(circle, 200);
     box = [0 10 0 10];
     res = clipPolyline(poly, box);
     figure;
     hold on; axis equal; axis([-2 12 -2 12]);
     drawCircle(circle, 'b:')
     drawBox(box, 'k')
     drawPolyline(res, 'linewidth', 2, 'color', 'b')
 
   See also:
     polygons2d, boxes2d, clipPolygon, clipEdge

0001 function res = clipPolyline(poly, box)
0002 %CLIPPOLYLINE Clip an open polyline with a rectangular box.
0003 %
0004 %   POLY2 = clipPolyline(POLY, BOX);
0005 %   POLY is N-by-2 array of vertex coordinates.
0006 %   BOX has the form: [XMIN XMAX YMIN YMAX].
0007 %   Returns the set of polylines created by the intersection of the
0008 %   polyline POLY and the bounding box BOX. The result is a cell array with
0009 %   as many cells as the number of curve clips.
0010 %
0011 %
0012 %   Example
0013 %     circle = [5 5 6];
0014 %     poly = circleToPolygon(circle, 200);
0015 %     box = [0 10 0 10];
0016 %     res = clipPolyline(poly, box);
0017 %     figure;
0018 %     hold on; axis equal; axis([-2 12 -2 12]);
0019 %     drawCircle(circle, 'b:')
0020 %     drawBox(box, 'k')
0021 %     drawPolyline(res, 'linewidth', 2, 'color', 'b')
0022 %
0023 %   See also:
0024 %     polygons2d, boxes2d, clipPolygon, clipEdge
0025 %
0026 
0027 % ---------
0028 % author : David Legland
0029 % created the 14/05/2005.
0030 % Copyright 2010 INRA - Cepia Software Platform.
0031 
0032 %   HISTORY
0033 %   2007/09/14 fix doc
0034 
0035 % check case of polylines stored in cell array
0036 if iscell(poly)
0037     res = cell(1, length(poly));
0038     for i = 1:length(poly)
0039         res{i} = clipPolyline(poly{i}, box);
0040     end
0041     return;
0042 end
0043 
0044 % check case of empty polylines
0045 N = size(poly, 1);
0046 if N == 0
0047     res = cell(0, 0);
0048     return
0049 end
0050 
0051 % create edges array of polyline
0052 edges = [poly(1:N-1, :) poly(2:N, :)];
0053 
0054 % clip edges
0055 edges = clipEdge(edges, box);
0056 
0057 % select non empty edges, and get their vertices
0058 % find clipped edges within box
0059 inds = sum(abs(edges), 2) > 1e-14;
0060 
0061 % find list of adjacent edges within box
0062 dinds = diff(inds);
0063 inds0 = find(dinds == 1) + 1;
0064 if inds(1) == 1
0065     inds0 = [1 inds0];
0066 end
0067 inds1 = find(dinds == -1);
0068 if inds(end) == 1
0069     inds1 = [inds1 N-1];
0070 end
0071 
0072 nClips = length(inds0);
0073 res = cell(1, nClips);
0074 for iClip = 1:nClips
0075     range = inds0(iClip):inds1(iClip);
0076     poly2 = [edges(range, 1:2) ; edges(range(end), 3:4)];
0077     res{iClip} = poly2;
0078 end