MATLAB Function Reference

convhull

Convex hull

Syntax

• K = convhull(x,y)
  [K,a] = convhull(x,y)
  

Description

K = convhull(x,y) returns indices into the x and y vectors of the points on the convex hull.

[K,a] = convhull(x,y) also returns the area of the convex hull.

Visualization

Use plot to plot the output of convhull.

Examples

• xx = -1:.05:1; yy = abs(sqrt(xx));
  [x,y] = pol2cart(xx,yy);
  k = convhull(x,y);
  plot(x(k),y(k),'r-',x,y,'b+')
  
  
  

Algorithm

convhull is based on Qhull [2]. It uses the Qhull joggle option ('QJ'). For information about qhull, see http://www.geom.umn.edu/software/qhull/. For copyright information, see http://www.geom.umn.edu/software/download/COPYING.html.

See Also

convhulln, delaunay, plot, polyarea, voronoi

Reference

[1]  Barber, C. B., D.P. Dobkin, and H.T. Huhdanpaa, "The Quickhull Algorithm for Convex Hulls," ACM Transactions on Mathematical Software, Vol. 22, No. 4, Dec. 1996, p. 469-483. Available in HTML format at http://www.acm.org/ pubs/citations/journals/toms/1996-22-4/p469-barber/ and in PostScript format at ftp://geom.umn.edu/pub/software/qhull-96.ps.

[2]  National Science and Technology Research Center for Computation and Visualization of Geometric Structures (The Geometry Center), University of Minnesota. 1993.

conv2

convhulln