[vtkusers] place arrows equally spaced along streamlines

Tue Mar 21 15:59:23 EDT 2017

It turns out that each direction for streamlines is in its own cell, so
vtkAppendArcLength works very nice. I'll move that to VTK.

Thanks Shawn!
Dan

On Mon, Mar 20, 2017 at 5:42 PM, Dan Lipsa <dan.lipsa at kitware.com> wrote:

> Shawn,
> I don't think this filter will work because you can interpolate in both
> directions from a seed which means that you'll have a jump between some
> points. Seems the easiest would be just to add an additional array in
> vtkStreamTracer.
>
> Dan
>
>
> On Mon, Mar 20, 2017 at 4:39 PM, Shawn Waldon <shawn.waldon at kitware.com>
> wrote:
>
>> Not VTK, but ParaView has a vtkAppendArcLength filter [1] that you can
>> use to append the distance along a polyline as a data array.  Then could
>> you use that to get your evenly spaced points?  It could be moved down into
>> VTK if someone needed it there.  I'm not sure how it handles multiple lines
>> in the input dataset though.
>>
>> Shawn
>>
>> [1]: http://www.paraview.org/ParaView/Doc/Nightly/www/cxx-doc/
>> classvtkAppendArcLength.html
>>
>> On Mon, Mar 20, 2017 at 4:22 PM, Andy Bauer <andy.bauer at kitware.com>
>> wrote:
>>
>>> For this you would have to normalize the vector after doing the
>>> interpolation instead of on the full velocity field.
>>>
>>> On Mon, Mar 20, 2017 at 4:13 PM, Andy Bauer <andy.bauer at kitware.com>
>>> wrote:
>>>
>>>> If exact math was done with integrating the streamlines you should get
>>>> the same result, regardless of the vector magnitude. Since we are
>>>> numerically integrating though it may be off a bit.
>>>>
>>>> On Mon, Mar 20, 2017 at 4:08 PM, Cory Quammen <cory.quammen at kitware.com
>>>> > wrote:
>>>>
>>>>> Dan,
>>>>>
>>>>> Actually, I think I'm wrong. I think you would get different
>>>>> streamline results by changing the vector magnitudes. You'll
>>>>> definitely get evenly spaced glyphs by normalizing, though :-) Too bad
>>>>> the streamlines will be wrong.
>>>>>
>>>>> I can't think of any other tricks using existing tools in VTK to do
>>>>> this - you would need a scalar field along the streamline giving the
>>>>> distance from seed point.
>>>>>
>>>>> Cory
>>>>>
>>>>> On Wed, Mar 15, 2017 at 9:20 PM, Dan Lipsa <dan.lipsa at kitware.com>
>>>>> wrote:
>>>>> > Thanks Cory!
>>>>> > This works very nice!
>>>>> >
>>>>> > Dan
>>>>> >
>>>>> >
>>>>> > On Wed, Mar 15, 2017 at 12:08 PM, Cory Quammen <
>>>>> cory.quammen at kitware.com>
>>>>> > wrote:
>>>>> >>
>>>>> >> Dan,
>>>>> >>
>>>>> >> Another way would be to normalize your vector field, run the stream
>>>>> >> tracer on it, and then contour by integration time. That should give
>>>>> >> you evenly spaced samples along the streamline when you run the
>>>>> >> contour filter on it.
>>>>> >>
>>>>> >> A quick test of this in ParaView looks like it should work. See
>>>>> >> attached images. The one with the normalized velocity field has even
>>>>> >> spacing, the one with the non-normalized velocity field does not.
>>>>> >>
>>>>> >> Cory
>>>>> >>
>>>>> >> On Wed, Mar 15, 2017 at 11:44 AM, Dan Lipsa <dan.lipsa at kitware.com>
>>>>> wrote:
>>>>> >> > Hi all,
>>>>> >> > I would like to place arrow glyphs equally spaced along
>>>>> streamlines. I
>>>>> >> > am
>>>>> >> > using vtkStreamTracer.
>>>>> >> > The only way I see to do this is to add an option to
>>>>> vtkStreamTracer to
>>>>> >> > compute the distance from the seed and add this as a point data
>>>>> to the
>>>>> >> > the
>>>>> >> > streamline. Than, I can use contour to get the points where I
>>>>> need to
>>>>> >> > place
>>>>> >> > the arrows.
>>>>> >> >
>>>>> >> > Is there any other simpler way? Do you have any suggestions with
>>>>> this?
>>>>> >> >
>>>>> >> > Thanks,
>>>>> >> > Dan
>>>>> >> >
>>>>> >> >
>>>>> >> > _______________________________________________
>>>>> >> > Powered by www.kitware.com
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>>>>> >> > Please keep messages on-topic and check the VTK FAQ at:
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>>>>> >>
>>>>> >>
>>>>> >>
>>>>> >> --
>>>>> >> Cory Quammen
>>>>> >> Staff R&D Engineer
>>>>> >> Kitware, Inc.
>>>>> >
>>>>> >
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Cory Quammen
>>>>> Staff R&D Engineer
>>>>> Kitware, Inc.
>>>>> _______________________________________________
>>>>> Powered by www.kitware.com
>>>>>
>>>>> Visit other Kitware open-source projects at
>>>>> http://www.kitware.com/opensource/opensource.html
>>>>>
>>>>> Please keep messages on-topic and check the VTK FAQ at:
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>>>>
>>>>
>>>
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>>
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