On Jun 21, 3:24 am, Wox <s...@nomail.com> wrote:
> On Sat, 18 Jun 2011 11:34:42 -0700 (PDT), Junum <junshi...@gmail.com>
> wrote:
>
>> Thanks Karl.
>> I wanted know whether IDLanROI::ContainsPoints can be applied to 3D
>> case.
>
> I'd guess the answer is no. You should implement this yourself (as
> Karl suggested) or you could do something like below. I'm not sure
> whether this is the best way, but it seems to work.
>
> ; Generate vertices
> v=TetrahedronVertices(r=10,phideg=-20)
>
> ; Connectivity list: [n,i[0],...,i[n-1],n,j[0],...,j[n-1],...]
> ; n: number of vertices for each face
> ; i[0],...,i[n-1]: vertices for face 1, ordered so that the normal
> ; points outwards (right-hand rule)
> ; j[0],...,j[n-1]: vertices for face 2, ordered so that the normal
> ; points outwards (right-hand rule)
> conn=[3,0,3,1, 3,0,1,2, 3,0,2,3, 3,1,3,2]
>
> ; Remark: if the number of vertices > 4 then you could generate
> ; the list like this:
> ;Qhull, v, tr, /delaunay
> ;conn=tetra_surface(v, tr)
>
> ; Point
> p=[0,0,0.]
>
> ; Volume of the polyhedron
> volume=tetra_volume(v,conn)
>
> ; Expanded polyhedron (including your point)
> ; vertices and connectivity list
> v2=[[v],[p]]
> Qhull, v2, tr, /delaunay
> conn2=tetra_surface(v2, tr)
>
> ; Volume of the expanded polyhedron
> volumeexp=tetra_volume(v2,conn2)
>
> ; If the "expanded volume" is larger, the point lies outside
> if volumeexp gt volume then print,'Exterior' else print,'Interior'
>> I wanted know whether IDLanROI::ContainsPoints can be applied to 3D
>> case.
>
> I'd guess the answer is no.
Right. Although not explicitly stated, I think that most of the anROI
support is for 2D ROI's even though you can specify points in 3D
space. The ROI's were intended for image analysis, I think. I
understand that ROI's can be 1D and 3D as well, but I think that the
algorithms in anROI are intended for 2D. Note that there are methods
to compute such things as area and perimeter, but not volume and
surface area. I also recall that some of the anROI algorithms will go
ahead and try to do things like compute areas for non-planar ROI's
even though the result may be questionable. Other algorithms might
actually go ahead and do a planarity check and throw an error if the
data wasn't planar.
The expanding polyhedron approach is clever! I like it.
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
![Karl[1] is currently offline](theme/default/images/xoffline.png.pagespeed.ic.XRkd1fkXye.png "Karl[1] is currently offline")
