[vtkusers] Plane polydata intersection

Mon Jun 24 10:20:15 EDT 2013

Hi Cory,

Thank you for your reply.

However, you said I have to compute distance from each point to my plane, then use vtkContourFilter.
But I think it would be really heavy computation to compute distance from each point to the plane every time I move the plane, isn't it ?

I would like to be able to display the intersection while the plane is moving. If I have a polydata like a bone or a skull or something like that, it would be really long to compute this distance, isn't it ?

Thank you.
-Laurent

On Jun 24, 2013, at 10:04 AM, Cory Quammen <cquammen at cs.unc.edu> wrote:

> On Sun, Jun 23, 2013 at 12:41 PM, Laurent Chauvin
> <lchauvin at bwh.harvard.edu> wrote:
>> Hi Cory,
>> 
>> Thank you very much for your reply.
>> However, I'm not sure to understand what you mean.
>> Should I create a new polydata with all points at the same z coordinates ?
> 
> Laurent,
> 
> You don't need to create a new polydata. Instead, you can add a new
> vtkDataArray (likely a vtkFloatArray or vtkDataArray in this case) to
> the point data of whatever polydata you already have by using
> vtkPolyData::GetPointData()->AddArray(...).
> 
> For axis-aligned planes, this new array could simply contain the x, y,
> or z coordinate of each of the points in your vtkPolyData. If you want
> an intersection of your poly data with a plane spanning x and y, you
> would add a point data array storing all the z values. You can then
> use the vtkContourFilter to get the polydata consisting of line
> segments that represents the intersection of your polydata with the
> plane at a given z value by specifying that z value as the isolevel
> for the contour filter. You have to make sure you tell the
> vtkContourFilter to use your new coordinate array.
> 
> For an quick example of this concept, I've attached a simple ParaView
> statefile showing how you can do this for a cylinder polydata. In this
> example, I've specified my plane as spanning the x and y coordinates
> with z value 0.2. In ParaView, I've used the Calculator to compute the
> array consisting of the z coordinates of each point in the cylinder.
> Forgive me if you don't have ParaView installed, we use it all the
> time when prototyping visualizations.
> 
>> Does this work with some oblique planes ( not parallel to x,y, or z axis ) ?
> 
> For the general case of an arbitrary plane, you would want to compute
> the distance from each point your desired plan instead of creating a
> new array containing the x, y, or z coordinates of each point. Then
> you would set the vtkContourFilter isolevel to 0. The point plane
> calculation is pretty simple:
> http://mathworld.wolfram.com/Point-PlaneDistance.html
> 
> Does that make sense?
> 
>> Thank you.
>> -Laurent
>> 
>> 
>> On Sun, Jun 23, 2013 at 12:31 PM, Cory Quammen <cquammen at cs.unc.edu> wrote:
>>> 
>>> Laurent,
>>> 
>>> For this special case of computing the intersection between a polydata
>>> and a plane, you can use a little trick. First, you can compute a new
>>> point data set for your polydata with,say, the z coordinates of each
>>> point in the polydata. Then, to get the intersection with an xy plane,
>>> you then use the vtkContourFilter operating on this coordinate point
>>> data and specify the z value that corresponds to your plane. The
>>> result should be equivalent to the intersection of the polydata with
>>> that plane.
>>> 
>>> It should be relatively fast to compute the contour, so you can
>>> probably do this interactively.
>>> 
>>> Hope that helps,
>>> Cory
>>> 
>>> On Sat, Jun 22, 2013 at 2:46 PM, Laurent Chauvin
>>> <lchauvin at bwh.harvard.edu> wrote:
>>>> Hello,
>>>> 
>>>> I'm working on Slicer, and I was trying to find a nice way to display
>>>> intersection between polydata and a plane.
>>>> I read we could use a vtkCutter, but the thing is, I would like to do
>>>> this
>>>> interactively. I want to be able to move the plane, and update the
>>>> intersection while moving the plane.
>>>> I'm not sure using vtkCutter for this purpose would work. I think
>>>> vtkCutter
>>>> will take some times to execute, then moving the plane will be slow.
>>>> 
>>>> I know this question has been asked before, but I would like if there
>>>> were
>>>> some update since then. New widgets or object that I could use for that
>>>> ?
>>>> 
>>>> I was thinking using vtkImageReslice, get polydata of the plane and
>>>> compute
>>>> the intersection between the 2 polydata, but I think it would also be to
>>>> computing intensive to be able to do it smoothly with an interactive
>>>> plane.
>>>> 
>>>> Thank you.
>>>> -Laurent
>>>> 
>>>> 
>>>> 
>>>> 
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>>> 
>>> 
>>> 
>>> --
>>> Cory Quammen
>>> Research Associate
>>> Department of Computer Science
>>> The University of North Carolina at Chapel Hill
>> 
>> 
>> 
>> 
>> --
>> Laurent Chauvin, MS
>> Surgical Navigation and Robotics Laboratory, Radiology
>> Brigham And Women's Hospital, Harvard Medical School
>> http://wiki.ncigt.org/index.php/User:Lchauvin
> 
> 
> 
> --
> Cory Quammen
> Research Associate
> Department of Computer Science
> The University of North Carolina at Chapel Hill
> <PlaneIntersectionExample.pvsm>

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