convex_hull - convex hull of a set of points in the plane

Calling Sequence

[nhull,ind] = convex_hull(xy)

Parameters

• xy : 2 x n real matrix
• nhull : integer
• ind : integer row vector

Description

convex_hull finds the convex hull of a given set of n points in the plane. xy is the 2 x n matrix of the (x,y) coordinates of the given points. convex_hull returns in nhull the number of the points of the boundary of the convex hull and in ind the row vector (of size nhull) giving the indices in xy of the points of the boundary. The order in ind corresponds to consecutive points on the boundary.

Examples

ta=[27 27 3 12 11 12 27 26 26 25 25 24 23 23 21 22 21 20 19 18 18];
ta=[ta  16 15 15 14 12 9 10 6 9 17 8 17 10 20 11 23 23 12 18 28]; 
he=[ 1  2 2  4  5 11 13  1 25 22 24 22 22 19 13 13 14 16 16  9 16];
he=[he  10 10 11 12  2 6  5 5 7  8 7  9  6 11  4 18 13  3 28 17];
g=make_graph('foo',0,28,ta,he);
xx=[46 120 207 286 366 453 543 544 473 387 300 206 136 250 346 408];
g('node_x')=[xx 527 443 306 326 196 139 264  55  58  46 118 513];
yy=[36  34  37  40  38  40  35 102 102  98  93  96 167 172 101 179];
g('node_y')=[yy 198 252 183 148 172 256 259 258 167 109 104 253];
show_graph(g);
xy=[g('node_x');g('node_y')];
[nhull,ind] = convex_hull(xy)
show_nodes(ind);