General Module Function
The streamline surface module is used to produce streamlines on any surface based on its slopes. Streamlines are 3D polylines representing the paths particles would travel based on the slopes of the input surface. The direction of travel of streamlines can be specified to be downhill or uphill for the slope case. A physics simulation option is also available which employs a full physics simulation including friction and gravity terms to compute streamlines on the surface.
Module Input Ports
Streamline surface has three input ports.
Data passed to the first port (the left port) must be a surface.
The second port accepts data specifying the starting location of the streamlines. This data is typically generated by the slice or isolines or place_glyph modules.
The last port is the z exaggeration factor. This input causes the stream path generation to be calculated in an unscaled system ensuring that velocities are not scaled and are accurate, then scales the position of the streamlines.
Module Output Ports
Streamline surface has two output ports. The leftmost output port creates a new unstructured polyline mesh representing the streamlines. The output also contains a nodal data component referencing the velocity component. The right output port can send either streamline polylines or renderable streamribbons to the viewer.
Module Control Panel
The control panel for streamline surface is shown in the figure above.
The Map Component radio button allows you to choose which computed data component to use for coloring the lines. Choices are Velocity, Time, Distance and Uncolored.
The Direction radio buttons allow the user to specify forward or backward streamlines. Forward streamlines start from the specified starting points and travel to the maximum velocity location. Backward streamlines travel from the specified starting points to the minimum or zero velocity location.
The Coloring Options radio buttons allow the user to specify Magnitude (normal) or Log10(Magnitude) representation of the velocity data for coloring purposes. When velocities span several orders of magnitude this is useful.
The Physics radio buttons allow the user to specify whether streamlines will be computed based on the slopes of the surface only or whether a full physics simulation including friction and gravity terms will be used to compute streamlines on the surface. When Gravity is selected Segments perCell and Order do not apply but additional parameters appear for the module. These are:
Integration Time Step is the time step for the numerical integration of the paths. For typical gravity units (like 32 feet per second-squared) this value is in seconds.
Gravity is the coefficient of gravity for your units. If your coordinate units are feet, the appropriate (default) value would be 32 feet per second-squared.
Viscosity Coefficient (v) is the friction term that depends on velocity.
Drag Coefficient (v2) is the friction term that depends on velocity-squared.
The panel when Gravity is selected is show below.
The Min Magnitude and Max Magnitude type-ins display the min/max velocities represented in the input field. Changing these values allows the user to reset the min-max values for coloring purposes. NOTE: once you change these values they will not automatically update.
The Z Scale type-in reflects the value of the z exaggeration port.
The Segment per Cell slider is used to set the number of integration steps to be used in each cell (i.e., the number of divisions of the cells) to calculate the streamline. The default is one and the range is 1 to 16.
The Max Segments Total slider is used to set the maximum allowable number of streamline segments that will be completed for each streamline. If the number of segments along a streamline exceeds the max number, the streamline is terminated at the end of the last (max) segment. The default is 15 and the range is 1 to 1000.
The Order slider is used to set the order of the integration. Higher order integration is more accurate, but executes much slower. The default is one and the range is 1 to 4.
The Min Velocity slider and type-in is used to specify the minimum velocity that will be considered in the integration. If the magnitude of the velocity field in a region is less than this minimum value, streamlines will end in that region (or will not be produced if the gradient at a starting point is less than the min). Setting this to a lower value will produce longer streamlines (and typically more). Higher values tend to produce less streamlines and shorter streamlines. If streamlines are not visible on the data set, setting this to a lower value may produce streamlines. The default value is 0.000001.
The Extinction Angle slider is used to specify the maximum allowable angle between successive line segments before integration (streamline generation) should be terminated. The default value is 130 degrees.
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