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## Setting the streamline source

The Streamline plot's source type determines the geometry of its seed points, which are the points from which streamlines are calculated. Five different source types: Point, Line, Plane, Sphere, and Box are available in the Source type menu on the Streamline source tab of the Streamline plot attributes window. You can select a new source type by selecting one of the source types in the Source type menu. Once a new source type is selected, the area immediately below the Source type menu, known as the Source type area, changes to reflect the source type that was selected. For example, if a Box source type was selected, the Source type area changes to show the text fields used to specify coordinates for the box.

For Point source types, the Source type area displays a single text field into which you can type a 3D point to specify the location of the point.

Figure 39

When the source type is set to Line (see figure), the Source type area displays two text fields that allow you to enter 3D points for the start end and locations of the source line. The Streamline plot creates a number of points, specified by the point density, along the length of the source line. More seed points can be added along the length the source line by increasing the point density, which you can do by typing a larger number into the Point density text field or by clicking on its up arrow. The endpoints of the source line can also be modified using VisIt's interactive Line tool. First make sure that the Streamline plot is selected in the Main Window's Plot list and then enable the Line tool using the visualization window's toolbar or its popup menu. When the Line tool is enabled, moving its endpoints supplies the Streamline plot with new endpoints for its source line and the plot calculates new streamlines.

Figure 40

When the source type is set to Plane (see figure), the Source type area displays four text fields that allow you to enter a plane equation for the source plane. To move the source plane, you type a new 3D point into the Origin text field. To change the orientation of the source plane, you type a new 3D vector, the plane normal, into the Normal text field. The plane normal is a vector that is perpendicular to the source plane. Together with the plane origin, this is all that is necessary to specify a plane in 3D. However, more information is needed to specify the bounds of the source plane. For this purpose, the Streamline plot attributes window provides the Up axis and Radius text fields. Imagine a square, centered at the plane source origin, that lying in the same plane as the plane source. The distance to one of the square's corners is the plane radius. The plane radius determines the size of the plane source and it can be changed by typing a new value into the Radius text field. The up axis is a vector lying in the plane that determines which way is up for the square. You can change the up axis by typing a new 3D vector into the Up Axis text field. The Streamline plot creates a grid of evenly spaced seed points in the square defined by the source plane and source plane radius. The grid has a number of points equal to the point density plus one in both dimensions. The plane source can be modified using the controls in the Streamline plot attributes window or by using VisIt's interactive Plane tool. When a Streamline plot is selected the Plot list, moving the plane tool changes the source plane and the plot calculates new streamlines.

Figure 41

When the source type is set to Sphere (see figure), the Source type area displays two text fields that allow you to enter a sphere origin and radius to specify the source sphere. To move the source sphere, type a new 3D point into the Origin text field. To change the radius of the sphere, you type a new radius value into the Radius text field. The Streamline plot creates a number of seed points on the surface of the sphere and ,again, the number of points is a function of the point density. The sphere source can be modified using the controls in the window or by using VisIt's interactive sphere tool. When a Streamline plot is selected in the Plot list, moving the sphere tool changes the source sphere and the plot calculates new streamlines.

Figure 42

When the source type is set to Box (see figure), the Source type area displays three text fields that allow you to enter the minimum and maximum values for the x,y,z dimensions that are used to specify the box source. You can enter new minimum or maximum values by typing in the X Extents, Y Extents, or Z Extents text fields. The Streamline plot creates a 3D grid of evenly spaced seed points in the source box. The grid has a number of points equal to the point density plus one in all three dimensions. The box source can be modified using the window's controls or by using VisIt's interactive Box tool. When a Streamline plot is selected in the Plot list, moving the box tool changes the source box and calculates new streamlines.