Creating a Streamline plot
- Open up the example.silo database (the location will be wherever you started VisIt).
- Make a Streamline plot of the variable grad
- Draw Plots
You should see a single streamline, drawn as a line.
- Bring up the plot attributes for the Streamline plot and go to the "Appearance" tab.
- Change the "Draw as" value from "Lines" to "Tubes".
- Check the "Show seeds"
- Press the "Apply" button.
You should see the same streamline drawn as a tube, with the seed point displayed as a sphere.
You can assign colors to the points along the streamline in various ways.
- In the "Appearance" tab, change the "Data Value" to Arc length, and press "Apply". Each point in the streamline is colored by the length from the seed point.
- Change the "Data Value" to Variable.
- In the variable pull down, select "hardyglobal".
- Press the Apply button.
Now each point in the streamline is colored by the value of the variable at that position.
Seed point options
Go back to the "Streamlines" tab in the plot attributes window. The default seed is a single point at the location (0,0,0).
- Change the location to -3 4 1.
- Press the "Apply" button.
VisIt offers several different options for seed point generation.
- Change the "Source type" to Line.
- Set the Start to -5 0 0 and the End to 5 0 0
- Set "Samples along line" to 5.
- Press the "Apply" button. VisIt will uniformly sample 5 points along the definition of the line.
- Check the "Random" box.
- Set the "Number of Samples" to 5.
- Press the "Apply" button. VisIt will randomly sample 5 points along the definition of the line.
- Set the "Seed" to 8329, and press the "Apply" button. A different set of 5 random points will be sampled along the line.
Experiment with the other "Source type" options. The "Point List" option allows arbitrary points to be used as seeds, including reading a list of points from a text file. Each line must contain a single 3D point, with comma or whitespace between coordinates.
Seed points and Tools
The VisIt tools can be used to define the seed points within a streamline plot.
- Create a streamline plot using a line source.
- Select the streamline plot in the gui.
- Activate the line tool in the viewer window.
- Drag the hot spots on the line tool to update the definition of the line source.
VisIt provides three different techniques to perform numerical integration. The default method is Dormand-Prince, which is a Runge-Kutta based technique. The Adams-Bashforth multi-step technique is also available, as is the M3D-C1 (a technique specific to the M3D fusion code) method. In this section, we will focus on the Dormand-Prince integrator. The Dormand-Prince uses an adaptive step, which can be controlled with the "Maximum step length" attributed in the integration section. The relative and absolute tolerance attributes control the error at each integration step.