[vtkusers] Sphere with scalar values

[David Doria]

On Sat, Jan 16, 2010 at 3:14 PM, David Doria <daviddoria+vtk at gmail.com> wrote:
> On Sat, Jan 16, 2010 at 1:33 PM, David Doria <daviddoria+vtk at gmail.com> wrote:
>> On Sat, Jan 16, 2010 at 12:04 PM, KS Jothybasu <jothybasu at gmail.com> wrote:
>>> Hi David,
>>>
>>> What you said is true, finding  the points  inside the sphere and setting
>>> its scalar value.
>>>
>>> But, my problem is that, I need to move the sphere to multiple positions and
>>> do some calculations with the sphere scalar values and the scalar values of
>>> the vtkimagedata. If I can set the scalars to the sphere directly,I don't
>>> need to recompute those scalars for each and every position of sphere.
>>>
>>> Did you get it? I can give you some more explanation if you wish.
>>>
>>> Shall I create the sphere from scratch, as a vtkVolume/vtkPolydata, if so ,
>>> any examples...
>>>
>>>
>>> Thanks
>>>
>>> Jothy
>>>
>>> On Sat, Jan 16, 2010 at 4:52 PM, David Doria <daviddoria+vtk at gmail.com>
>>> wrote:
>>>>
>>>> On Sat, Jan 16, 2010 at 11:49 AM, KS Jothybasu <jothybasu at gmail.com>
>>>> wrote:
>>>> > vtkPSphereSource means "sphere source that supports pieces " as the vtk
>>>> > doc
>>>> > says.
>>>> >
>>>> > I don't understand what supporting pieces means.
>>>> >
>>>> > Regarding my sphere object.
>>>> >
>>>> > I need to create a sphere object, let's say 5 cm radius. Indise that I
>>>> > want
>>>> > to set scalar values as we set for vtkImageData with
>>>> > SetScalarComponentFromFloat(x,y,z,0,HU).
>>>> >
>>>> > Thanks
>>>> >
>>>> > Jothy
>>>> >
>>>> >
>>>> >
>>>> > On Sat, Jan 16, 2010 at 4:37 PM, David Doria <daviddoria+vtk at gmail.com>
>>>> > wrote:
>>>> >>
>>>> >> On Sat, Jan 16, 2010 at 10:30 AM, KS Jothybasu <jothybasu at gmail.com>
>>>> >> wrote:
>>>> >> > Hi,
>>>> >> >
>>>> >> > I am trying to create a sphere object comprising of voxels and
>>>> >> > setting
>>>> >> > the
>>>> >> > scalar values. But I am yet a find a proper method to do this.
>>>> >> >
>>>> >> > Could any of you please give me a hint?
>>>> >> >
>>>> >> > Should I create sphere object with polydata?
>>>> >> >
>>>> >> > What's the difference between vtkSphereSource and vtkPSphereSource
>>>> >> >
>>>> >> > Thanks
>>>> >> >
>>>> >> > Jothy
>>>> >> >
>>>> >>
>>>> >> If I understand correctly, vtkP* means it is a parallel version of the
>>>> >> vtk* filter. I don't think it has any relevance to your question.
>>>> >>
>>>> >> I guess I don't follow what you mean by "a sphere object comprising of
>>>> >> voxels". Can you elaborate or give an example?
>>>> >>
>>>> >> Thanks,
>>>> >>
>>>> >> David
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>>>> >
>>>>
>>>> Please keep the discussion on the mailing list.
>>>>
>>>> I agree that "supporting pieces" is not very clear. What I believe it
>>>> means is that the memory that comprises the object is split into
>>>> "pieces" which reside on multiple computers (hence, the parallel
>>>> version of the object).
>>>>
>>>> Why don't you just create an ImageData and for each point in the
>>>> ImageData test if it is inside your sphere. If it is, then set it's
>>>> scalar value.
>>>>
>>>> Will that work?
>>>>
>>>> Thanks,
>>>>
>>>> David
>>
>> Again, please keep the discussion on the mailing list.
>>
>> Can't you just apply the transformation that you would have applied to
>> the sphere to the ImageData instead to position the scalars in your
>> scene?
>>
>> Thanks,
>>
>> David
>>
>
> Ok, so I take back what I said. An ImageData is always axis-aligned
> with the global coordinate system. Same with a RectilinearGrid. Looks
> like you'd need to use a StructuredGrid and specify the points as they
> would be implicitly in an ImageData. THEN you can apply a general
> transform to them.
>
> Let me know if that works.
>
> Thanks,
>
> David
>

By the way, I think you'd want to use this to check if the points on
your grid are inside the sphere:

http://www.cmake.org/Wiki/Check_if_a_point_is_inside_an_object

Thanks,

David