Re: [opendx-users] Streamlines

[Frederick R. Phelan Jr.]

Thanks for your reply ...

I know that streamlines should not look exactly like the glyphs per se, but what I meant was that the shape of the streamlines does not seem to correspond to the computed velocity field, and since the velocity field looks good, I conclude that I am screwing up the DX stuff!

I think the problem is that I am not specifying the "START" data component of the STREAMLINE module correctly. The default value for this is "center of object" and given that, the one streamline I see does make sense ... it starts at the center of the mesh, and terminates at the boundary.

Seems like I somehow need to give the STREAMLINE module the grid positions and I am not sure how to do that ... Anyone got an idea??? I tried specifying "positions", but that did not work.

Thanks,
Fred Phelan

At 08:01 AM 4/6/01 -0400, you wrote:
>>Can DX render streamlines from 2-D velocity data?
>>
>>I am passing the velocity data through the sequence:
>>
>>{velocity} -> STREAMLINE -> AUTOCOLOR -> IMAGE
>>
>>But I get a very strange rendering that looks nothing like the
>>glyphs of the velocity field.
>>
>>Also tried:
>>
>>{velocity} -> STREAMLINE -> AUTOCOLOR -> ISOSURFACE -> IMAGE
>>
>>But that gave an error!
>>
>>Thanks,
>>Fred Phelan
>
>
>Streamline purports to take n-vectors mapped in n-space. If you have
>2-d vectors on 2-d positions, it should work. If not, you can promote
>or demote data or positions with Mark, Compute, Unmark by adding a
>bogus (0 valued) 3rd dimension to data or chopping off a dimension
>from positions.
>
>Streamlines should not look like vector glyphs, that's what we have
>the vector glyph for! Streamlines look like lines generally speaking.
>However, you should be able to take the output of streamline as input
>to Glyph (maybe with a bit of munging, I can't remember). Use
>Print("rd") on Streamline's output to see if you have vector data
>mapped to positions. If so, make sure the vector data is the "data"
>(Mark if necessary), then Glyph should take it and you'll see the
>streamline as a set of glyphs pointing along the direction vector
>(presumably). You'll note that streamline output has a bunch of other
>handy stuff, like "time" which can be used cleverly. Hint: we Map
>streamlines to a discretized time line (Construct'ed) so Sequencer
>can clock out a nice animation of equal steps along a streamline.
>Exercise left to reader (or highly paid consultant, like, oh say, me).
>
>Naturally, your latter trick didn't work above since a streamline is
>a graphic object (not a data object per se), not likely to be a
>compatible input to the isosurface function.
>
>Chris Pelkie
>Vice President/Scientific Visualization Producer
>Conceptual Reality Presentations, Inc.
>30 West Meadow Drive
>Ithaca, NY 14850
>[EMAIL PROTECTED]

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Frederick R. Phelan Jr., Ph.D.
Multiphase Materials Group
Polymers Division
National Institute of Standards and Technology

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