>I used a Pick to draw 2-D stream line, but it didn't work. Pick returns 3-D >point (x, y, z), and my 2-D stream line only requires (x, y). I used Compute >to extract only (x, y), but it still didn't work. What's the problem? >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
