Kevin Wampler wrote:
> Tom Austin wrote:
>>
>> Methods or programs to 'simplify' the resulting point cloud so that it 
>> still is a fair representation of the overall area, but has much fewer 
>> points ~300k.
>>
>> Methods or programs to create a single mesh of the resulting point 
>> cloud that can represent tunnels.
>>
> 
> 
> That's a nifty problem! I might have some ideas, but first I have a few 
> questions about it:
> 

It's actually pretty fun - if only I had lots of time to work on it!


> * I'm talking it that each scan was done from a different location, so 
> while each individual scan can be represents a `spherical' cloud of 
> points the union of the scans does not?
> 

Yes - exactly



> * I assume that the final goal is the mesh and that the first task is 
> just needed so that the resulting mesh is relatively small?  I ask 
> because if so then it might be reasonable to generate a large mesh and 
> then simplify it later, which would allow different algorithms.
> 

a possible final result is a mesh

I may use an AutoCAD 3D solid or just the simplified points themselves.

I am still interested in what may work on meshes as opposed to points as 
the final product may be a mesh.


> * In terms of simplifying the point cloud/mesh, what are the accuracy 
> requirements of the simplification with respect to the density of the 
> point cloud from the scans?  In other words, if the scans are very dense 
> but you don't actually need that sort of accuracy in the mesh/simplified 
> cloud then you can probably get away with simpler algorithms than if you 
> need really high resolution in some areas and can only get away with 
> discarding points which don't contribute anything useful to the 
> geometry.  For instance, would it be sufficient to simplify the point 
> cloud by simply discarding all points which are within, say 10cm, of 
> each other?
> 

That's some of what I've been thinking about - simplifying where 
possible, and providing some more detail where the *object* is more complex.

I would like to figure out a relatively simple method of simplifying the 
mesh so that the actual work involved is low - even if processing time 
is high.




> * Have you tried existing approaches for generating a mesh from a point 
> cloud?  If so, did they not work because you have too many points for 
> them to operate effectively?

Honestly, I have not worked with anything to make a 3D mesh out of a 
*unified* pointcloud of several scans.

I have made meshes out of 2D point clouds (terrain) made from several scans.

I have made 3D meshes with only 1 scan (somewhat easy).




I'll try to make some time tomorrow to post a video of what I have done 
in the past so that you can get a better idea.







Tom

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