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## Streamline Plot

Figure 37

Figure 38

The Streamline plot (example shown in figure) shows the behavior of particles in a vector field. The Streamline plot calculates the value of the vector field at seed locations, which are produced by point sources, and integrates through the vector field to create a streamline. Streamlines can be displayed as a line, a tube, or as a ribbon if you also want to show the vorticity of the vector field. Once a set of streamlines is produced, vortices, etc present in the vector field are apparent in the visualization. The Streamline plot is special among VisIt's plots in that it can be modified using VisIt's interactive tools. For instance, if the Streamline plot is set to use a Plane source for its seed points, moving VisIt's Plane tool will move the plane that the Streamline plot uses forcing VisIt to recalculate the plot's streamlines using the new plane. For more information on interactive tools, see the Interactive Tools chapter.

VisIt's Streamline plot must be initialized more completely before you click the Draw button to generate the plot. First of all, you must take special care to set the step length, which is the maximum length that will be integrated through the vector field for each step. The step length should be set to a value approximating the average width of the cells in the mesh to ensure that the streamlines are as accurate as possible. After choosing a suitable step length, be sure to specify a maximum number of steps. The maximum number of steps is the number of integrations that will be performed for each streamline. In a vector field that is free of attractors, a larger number for maximum steps will generate longer streamlines.