Menu: Vies results->Stream lines
Toolbar: 
With this option you can display a stream line, or in fluid dynamics, a particle tracing, in a vector field. After choosing a vector result, using the default analysis and step selected, the program asks you for a point from which to start plotting the stream line. This point can be given in several ways:
The best way to choose initial points for the stream lines is to cut the mesh through the place where the user wants the stream lines, and then select the nodes of this cut.
- Clicking on the screen: The point will be the intersection between the line orthogonal to the screen and the plane parallel to the screen and containing the center of rotation.
- Joining a node: The selected node will be used as a start point.
- Selecting nodes: Here several nodes can be selected to start with.
- Along line: With this option you can define a segment along which several start points will be chosen. The number of points will also be asked for, including the ends of the segment. In the case of just one start point, this will be the center of the segment.
- In a quad: Here you can enter four lines that define a quadrilateral area which will be used to create a N x M matrix of points. These points will be the start for the stream lines. When giving N x M, N lies on the first and third line, and M on the second and fourth. So, points (0, 0..N), (M, 0..N), (0..M, 0) and (0..M, N) will lie on the lines. But in case of N=1 or M=1, this will be the center of the line, and if N = 1 and M = 1, this will be the center of the Quad.
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When creating a stream line, the user can tell GiD to create a stream line 2D constraint, by selecting this option of the right mouse button contextual menu. Then the stream line algorithm will discard the z coordinate of the meshes and of the vector field.
When viewing Stream Lines, labels can be drawn to show the times at the start and end points of the stream line.
Stream lines can also be deleted and their color changed (green by default).
Stream lines are supported for results defined over nodes.
The there are complex vectors, the user can select between the real part ( field) of the complex vector and the imaginary part ( field).
Go to Preferences --> Postprocess --> Stream lines to set and manage stream lines options, like the colours colors used, style which with they are drawn, etc. (see Stream lines)