Vis5D Documentation
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# Wind Trajectories

Wind trajectories trace the motion of air through the 3-D volume much line smoke trails in a wind tunnel. To enter trajectory mode select the TRAJECTORY radio button on the control panel. A pop-up window will appear near the bottom of the screen and a 3-D cursor will appear inside the 3-D view box. This 3-D cursor is used to specify where a new wind trajectory should be made. The STEP button on the main control panel is also important because it is used to select the time step at which to create the trajectory.

Wind trajectories are dealt with in sets. Currently, eight sets are available. Each set is represented in the trajectory window with a button labeled Set1, Set2, ..., Set8. Each set can be individually displayed, colored, or deleted. As you create new trajectories you may want to group them in sets corresponding to location, time, etc.

The first step in creating a trajectory is to select a position with the 3- D cursor. Use the right mouse button to drag the 3-D cursor around inside the 3- D box. The 3-D cursor will move in 2-D in a plane parallel to the plane of projection. That is, the cursor will stay at a constant distance of depth. By alternately rotating the view box with the left mouse button and placing the cursor with the right mouse button, the 3-D cursor can be placed anywhere inside the view box. The TOP, SOUTH, and WEST buttons as explained in section 6.2 can also be useful when making trajectories.

Second you should select a time step with the STEP button on the control panel. When the trajectory is made, it will be traced forward from the current time step to the last time step and will be traced backward through time to the first time step.

Finally, to make a trajectory at the current cursor location and current time step, press the middle mouse button when pointing inside the 3-D window. The trajectory will appear as a line segment. By turning on the ANIMATE button, you can observe how the trajectory travels through time and space. Typically, you will repeat the process of positioning the 3-D cursor and clicking the middle mouse button to create a set of trajectories.

Interesting results can be seen by making a trajectory when the ANIMATE button is turned on: a trajectory will be created for every time step instead of just one. This will show you the path of every air parcel which passes through a single point in space.

Here is a summary of the various trajectory functions:

1. To position the 3-D cursor, use a combination of rotating the view box with the left mouse button and dragging the 3-D cursor with the right mouse button.

2. Use the STEP button or ANIMATE option to select a time step.

3. Press the middle mouse button to create a trajectory at the current cursor location and time step.

4. To toggle the display of a trajectory set on or off, click on the set button with the left mouse button.

5. Select the current trajectory set by clicking on the set button with the middle mouse button.

6. A trajectory set may be deleted with the 'Delete Set' button in the trajectories window. You will asked to verify your decision.

7. You can delete the last trajectory made by clicking on the 'Delete Last' button in the trajectories window.

Wind trajectories can be depicted in two ways: as line segments or as ribbons. You can select ribbons by clicking on the RIBBON button in the trajectory window. Toggling the RIBBON button will not effect trajectories you have already made; it only controls how new trajectories will be displayed.

The trajectory window also contains two type-in widgets labeled STEP and LENGTH. The STEP value is used to control the step size used in the trajectory tracing algorithm. The LENGTH value is used to control the length of trajectories. 1.0 is the default value for each. Each acts as a multiplier. If you want the trajectory tracer to integrate in steps 1/2 the default size, enter a step value of 0.5. If you want trajectories to be twice as long as the default length, enter a length value of 2.0

The color of trajectories is controlled in the same way as for isosurfaces. That is, a trajectory set may either be mono-colored or colored according to another physical variable. Click on the trajectory set button with the right mouse button to bring up its color window. See section 6.5.1 for details on using the color window.

When viewing color-mapped trajectores be aware that the color of a trajectory is time dependent. Only the head of the trajectory is colored according to the value of another variable for the current time step. The tail of the trajectory is colored according to the color of the other variable when the head was at that location.

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