Hi Gianluca, 
 I think the issue might be that the normal, being the average of the cell 
normals around the point, is not reflecting the actual orientation of the 
surface with the needed accuracy.
Unfortunately at the present stage the script does only output the distance to 
the closest surface point, not to the node. You would have to work in VTK 
directly to achieve this, in 
a rather easy way, though. Specifically, take a look at the vtkPointLocator 
class, it does what you need.

The "right" way of doing what you need is probably to compute cell normals 
(vmtksurafcenormals -cellnormals 1), locate the closest cell (or the closest 
cells) and dot the point-cell distance with the cell normal.

Just  my 2 cents


Luca


On Feb 13, 2012, at 5:53 PM, gianluca de santis wrote:

> Dear Luca,
> 
> I am using the vmtksurfacedistance to check whether a point is inside or 
> outside a closed manifold surface. 
> Points inside and points outside are generally correct but sometimes I get a 
> wrong sign.
> By looking at the wrong points it seems that a wrong sign is assigned when 
> the closest surface point (on the distancevectorsarray) 
> is too close to a surface node or a surface edge.
> 1) The distancevectorsarray is correct. So, is it possible that during the 
> DOT product, the normal is not well defined if the point is too close 
> to a node or an edge?
> 2) Is it possible to force vmtksurfacedistance to return the 
> distancevectorsarray with the closest surface nodes (cartesian distance) 
> instead of closest surface points? In this way, one could calculate the dot 
> product outside vmtksurfacedistance.
> 
> Kind regards
> Gianluca 
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