[vtkusers] Sphere with scalar values

[David Doria]

On Sat, Jan 16, 2010 at 5:02 PM, David Doria <daviddoria+vtk at gmail.com> wrote:
> 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
>

Now that I'm having a conversation with myself... (sorry! haha)

If you come up with better methods for accessing points in a
structured grid (there should be an API similar to ImageData since the
topology is the same as imageData, no?), can you please let me know or
fix this example:

http://www.cmake.org/Wiki/VTK/Examples/StructuredGrid

Thanks,

David