Syntax is: pcl_compute_hull input.pcd output.vtk [optional_arguments]
Compute the convex or concave hull of a point cloud. For more information, use: pcl_compute_hull -h
where the optional arguments are:
-alpha X = the alpha value for the ConcaveHull (Alpha Shapes) algorithm. If alpha is not specified, the tool will run the ConvexHull method (default: 0.150000