[vtkusers] Combining three velocity components

[Adam Wiktor]

Wes,

The problem is that I need the overall velocity as a single vector, not the
components. I think I still need the calculator to sum the three components
to give the velocity. How would I do that?

Thanks,

Adam

On Fri, Jul 31, 2009 at 3:58 PM, Wes Turner <wes.turner at kitware.com> wrote:

> If you are just trying to get an image with three components corresponding
> to the x, y, and z, then that is what you should have as the output of the
> append filter.  The data at that point is not stored in separate x, y, and z
> vectors, but is instead a single multicomponent image.  You should have no
> need of the image calculator at that point.
> - Wes
>
>
> On Fri, Jul 31, 2009 at 3:24 PM, Adam Wiktor <awiktor at emory.edu> wrote:
>
>> Yes, I tried both that and AppendFilter, but I'm still having problems. I
>> may not be using the append correctly, but the calculator is only
>> recognizing one of the three components, and I get this error message (it's
>> the same for both ImageAppendComponents and AppendFilter):
>>
>> ERROR: In /home/awiktor/Desktop/VTK/Graphics/vtkArrayCalculator.cxx, line
>> 338
>> vtkArrayCalculator (0x763d70): Invalid array name: y
>>
>> I get the same message except with "Invalid array name: z" if I remove all
>> references to y, so I think this means that the calculator isn't seeing the
>> 'y' and 'z' variables.
>>
>> Here's the part of the code that isn't working:
>>
>> append=vtk.vtkImageAppendComponents()
>> append.AddInput(xcalc.GetOutput())
>> append.AddInput(ycalc.GetOutput())
>> append.AddInput(zcalc.GetOutput())
>> append.Update()
>>
>> velcalc = vtk.vtkArrayCalculator()
>> velcalc.SetInput(append.GetOutput())
>> velcalc.AddVectorArrayName("x", 0, 1, 2)
>> velcalc.AddVectorArrayName("y", 0, 1, 2)
>> velcalc.AddVectorArrayName("z", 0, 1, 2)
>> velcalc.SetResultArrayName("Velocity")
>> velcalc.SetFunction("x+y+z")
>> velcalc.Update()
>>
>> Any idea what the problem is?
>>
>> Thanks,
>>
>> Adam
>>
>>
>> On Fri, Jul 31, 2009 at 12:54 PM, Wes Turner <wes.turner at kitware.com>wrote:
>>
>>> Did you try ImageAppendComponents?
>>> http://www.vtk.org/doc/nightly/html/classvtkImageAppendComponents.html
>>>
>>>  <http://www.vtk.org/doc/nightly/html/classvtkImageAppendComponents.html>-
>>> Wes
>>>
>>> On Fri, Jul 31, 2009 at 12:16 PM, Adam Wiktor <awiktor at emory.edu> wrote:
>>>
>>>> Hi All,
>>>>
>>>> I am fairly new to VTK, so please bear with me. I'm trying to visualize
>>>> blood flow in the aorta from MRI scans. The velocity data is stored in three
>>>> separate vti images, for the x-, y- and z- components. Each image has a
>>>> scalar variable 'DICOMImage' which is the speed in that direction. I need to
>>>> combine the components into the overall velocity, which I will then import
>>>> into paraview to add streamlines and other things.
>>>>
>>>> My original thought was to use the vtkArrayCalculator to multiply each
>>>> image by the unit vector (for the x component, for example, it would be
>>>> DICOMImage*iHat). I would then need to combine these vectors into the
>>>> velocity with another calculator, just doing x+y+z. I might be able to
>>>> simplify this by just using one calculator that did x*iHat + y*jHat +
>>>> z*kHat, but I don't know how to change the variable names from DICOMImage to
>>>> x, y, and z so that the calculator can distinguish between them.
>>>>
>>>> First of all, I'd like to know if there's an easier way of doing this.
>>>>
>>>> If there isn't a more straight-forward way, then the main thing I need
>>>> to figure out is how to get the final calculator to use the three different
>>>> inputs. What would be the best way to do that?
>>>>
>>>> Thanks for any help you can give!
>>>>
>>>> - Adam
>>>> _______________________________________________
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>>>>
>>>
>>>
>>> --
>>> Wesley D. Turner, Ph.D.
>>> Kitware, Inc.
>>> R&D Engineer
>>> 28 Corporate Drive
>>> Clifton Park, NY 12065-8662
>>> Phone: 518-371-3971 x120
>>>
>>
>>
>
>
> --
> Wesley D. Turner, Ph.D.
> Kitware, Inc.
> R&D Engineer
> 28 Corporate Drive
> Clifton Park, NY 12065-8662
> Phone: 518-371-3971 x120
>
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