| Re: Point Cloud Isosurface [message #72060] |
Fri, 13 August 2010 10:15  |
tegus
Messages: 20
Registered: October 2008
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Junior Member |
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On Aug 13, 10:58 am, Karl <karl.w.schu...@gmail.com> wrote:
> 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.
Karl,
Thank you for your insight. This helps a great deal!!
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