Thanks for your reply. The objects I'm using are: Pick -> Extract -> Compute -> Select -> Streamline
All the data I'm using are 2-D, but I still can get the streamline. If I input the starting point directly in the configure control, then it works correctly. Pick returns a 3-D vector, we can't get the correct 2-D vector from this 3-D vector, is that right? Thanks. yuzhong > > Compute does convert a 3-vector [a.x, a.y, a.z] to 2-vector with an > expression like: > [a.x, a.y] > > but it isn't accurate to say it extracts the vector. More precisely that > implies to me that you extract a vector object (array) out of the field > component in which the vector is embedded (the Pick structure). In fact, > Compute does not do this. To put it another way, if the field had a data > component with 100 3-vectors, and you passed it through the above Compute > you'd get out a field with a data component that had 100 2-vectors. > > If you read the help carefully for Streamline, it accepts a bare list > (array) of vectors, including a single vector, or a geometric field. That > means that it would use the "positions", not the "data" of the supplied > field. > > Try simply entering (typing directly into the configuration dialog box) a > 2-vector value as the "starting point" for Streamline, giving it a known > good start value for your vector field and check that that works. Remember > that this must be a single vector or list of vectors, not a field of > vectors. Furthermore, the vector field you are trying to make a streamline > through must have the same dimensionality as the space in which it is > embedded. > > If you have a field of vectors that you want to be starting points, use > Extract to get the vector component out of the field. This is an "array" > that can be piped to Streamline start. Optionally, use Select(array, index) > where array is the thing you just Extracted, and index is a 0-based index > into that array (only 1D). This should return a single vector which can be > piped to Streamline start. > > If that doesn't work, check to see that the Streamline settings haven't > been changed in some way that cause the streamline to terminate immediately > (or shoot out of the domain immediately). > > Chris Pelkie > Vice President/Scientific Visualization Producer > Conceptual Reality Presentations, Inc. > 30 West Meadow Drive > Ithaca, NY 14850 > [EMAIL PROTECTED] > (607) 257-8335 or (607) 254-8794 > >
