   boundary mesh of a volume
  I have a volume data set.  Basically, each voxel is a value from 0 to255.  I define 0 as empty space.  All nonzero voxels form part of thevolume object of interest.  I would like to create a triangular meshof the boundary of the object.Marching cubes seems ideal but with this volume data, it is not thecase that all voxels on the boundary have the same value; that is, theboundary is not an isosurface.I could probably modify marching cubes to work, but I am wondering ifthere is another algorithm for what I think is an easier case than themore general marching cubes.   
  Hi, I have already modified Marching Cubes to work in exactly the way you describe. If you are interested I have an Open Source (GPL) library you can use (it's not finished, but is perfectly usable). It has no dependancies and is pure C++. You can find out more here: http://www.thermite3d.org. You just need the 'PolyVox' library, not the whole 3D engine.Website is work in progress, in particular the info on building from source is very out of date. Let me know if you want more information.   