you should be able to just pass the vector field in as the "start" parameter (or at least you can Extract the "positions" component of the grid and pass that in). You may want to investigate the Sample module for sampling your input field to get fewer (or more) points than just the grid vertices.
_________________________________ Donna L. Gresh, Ph.D. Visual Analysis Group IBM T.J. Watson Research Center (914) 784-5049 [EMAIL PROTECTED] "Frederick R. Phelan Jr." <[EMAIL PROTECTED]>@opendx.watson.ibm.com on 04/06/2001 10:47:15 AM Please respond to [email protected] Sent by: [EMAIL PROTECTED] To: [email protected] cc: Chris Pelkie <[EMAIL PROTECTED]> Subject: Re: [opendx-users] Streamlines 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] Frederick R. Phelan Jr., Ph.D. Multiphase Materials Group Polymers Division National Institute of Standards and Technology NIST, Bldg. 224/Rm. B108 100 Bureau Dr., STOP 8543 Gaithersburg, MD 20899-8543 301.975.6761 (VOX) 301.975.4932 (FAX) [EMAIL PROTECTED] http://www.nist.gov/frederick_phelan
