[vtkusers] Combining three velocity components
Dominik Szczerba
dominik at itis.ethz.ch
Mon Aug 3 10:27:31 EDT 2009
x y z are coordinates, I dont see how you can say velocity = x + y + z.
Adam Wiktor wrote:
> Yes, that's the formula for it, but what I can't figure out is the
> actual code for the calculator. After doing the ImageAppendComponents, I
> need to find a way for the calculator to do that operation on all three
> variables. Right now, it isn't recognizing the y and z components. How
> do I pass those two variables to the calculator so that it will
> recognize all three?
>
> This is what I have right now, but as I said, it only accepts the 'x'
> component and gives me an "invalid array name" error for the other two.
>
> 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()
>
> Thanks,
>
> Adam
>
> On Fri, Jul 31, 2009 at 4:53 PM, Dominik Szczerba <dominik at itis.ethz.ch
> <mailto:dominik at itis.ethz.ch>> wrote:
>
> u*iHat+v*jHat+w*kHat
>
> Adam Wiktor wrote:
>
> 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 <mailto:wes.turner at kitware.com>
> <mailto:wes.turner at kitware.com <mailto: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 <mailto:awiktor at emory.edu>
> <mailto:awiktor at emory.edu <mailto: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 <mailto:wes.turner at kitware.com>
> <mailto:wes.turner at kitware.com <mailto: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 <mailto:awiktor at emory.edu>
> <mailto:awiktor at emory.edu <mailto: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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>
> Visit other Kitware open-source projects at
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> http://www.vtk.org/Wiki/VTK_FAQ
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