| Re: Point Cloud Isosurface [message #72061 is a reply to message #72060] |
Fri, 13 August 2010 07:58   |
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Karl[1]
Messages: 79
Registered: October 2005
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On Aug 12, 7:55 pm, tegus <tegusbillhar...@gmail.com> wrote:
> On Aug 12, 5:27 pm, Karl <karl.w.schu...@gmail.com> wrote:
>
>
>
>> On Aug 12, 2:42 pm, tegus <tegusbillhar...@gmail.com> wrote:
>
>>> Hello,
>>> I'm working with noisy 3D point cloud data approximated by:
>>> xyz_0=randomn(seed, 3, 1000) + 5.0
>>> xyz_1=randomn(seed, 3, 1000) + 10.0
>>> xyz_2=randomu(seed, 3, 10000) * 20.0
>>> xyz=[[xyz_0], [xyz_1], [xyz_2]]
>
>>> although the actual data sets are larger and far more complex ...
>
>>> My current method of reducing and rendering the data:
>>> - Create a 3D histogram (bin size = 1) using hist_nd from JDHU
>>> library:
>>> vol=hist_nd(xyz, 1.0)
>>> - Create isosurface (density threshold=10)
>>> isosurface, vol, 10, verts, conn
>>> - Create polygon object and display
>>> oPoly=obj_new('IDLgrPolygon', verts, polygons=conn)
>>> xobjview, oPoly
>
>>> This gives me the desired result which in this example is a polygon
>>> object which depicts two blobs approximating the measured positions.
>
>>> However, rendering and analysis of a more complex scene as a single,
>>> complex polygon becomes unwieldy (e.g., no dynamic culling, z
>>> clipping ...)
>>> My question is, how do I separate these two solid objects, represented
>>> by a single polygon (verts and conn), into two seperate polygon
>>> objects (verts1, conn1 and verts2, conn2)?
>
>>> Thanks,
>>> Bill
>
>> MESH_CLIP() ?
>
> Karl,
>
> To use MESH_CLIP I need to specify a clipping plane between the blobs,
> which becomes intractable for any real data set (on the order of
> millions of points and tens of thousands of blobs).
oh ok. The conn list is a vector where each polygon is represented by
"n", followed by n vertex indices. So you could extract the first
polygon (blob) by:
blob_conn1 = conn[0:conn[0]]
and then generate additional conn lists for each blob by looping
through the original list.
These lists refer to the original vertex list. You can leave it that
way and just reference the original vertex list from the grPolygon
objects. So you would use verts (the original vert list) and
blob_conn1 in a grPolygon object to represent the first blob.
If putting the entire vertex list in each polygon object is bad, as I
suspect it is, you can do additional work to pull the vertices
referenced by each conn list out of the original vert list and make a
new, smaller, vert list for each blob. Then you can delete the
original vertex list.
This will likely be a good path since there are likely no shared verts
between blobs.
You'll have to be careful when pulling the verts out since you'll have
to remap the conn indicies and pay attention to verts used more than
once, etc. But it can all be done pretty easily.
And all this assumes that each blob is represented by one polygon in
the original polygon object. If that is not the case, you'll have to
do some more work to find all the polys that belong to a blob.
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