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## Setting the 3D view

Figure 34

Setting the 3D view using controls in the View Window's 3D view tab (see figure) demands an understanding of 3D views. A 3D view is essentially a location in space (view normal) looking at another location in space (focus) with a cone of vision (view angle). There are also clipping planes that lie along the view normal that clip the near and far objects from the view. figure depicts the various components of a 3D view.

To set the 3D view, first decide on where you want to look from. Type a vector value into the View normal text field. Next, type the vector valued location of what you want to look at into the Focus text field. The Up axis vector is simply a vector that determines which way is up. A good default value for the up axis is 0 1 0. VisIt will often calculate a better value to use for the up axis so it is not too important to figure out the right value. The View Angle determines how wide the field of view is. The view angle is specified in degrees and a value around 30 is usually sufficient. Near clipping and Far clipping are values along the view normal that determine where the near and far clipping planes are to be placed. It is not easy to know that good values for these are so you will have to experiment Parallel scale acts as a zoom factor and larger values zoom the camera towards the focus. The Perspective check box applies to 3D visualizations and it causes a more realistic view to be used where objects that are farther away are drawn smaller than closer objects of the same size. VisIt uses a perspective view for 3D visualizations by default.

VisIt supports stereo rendering, during which VisIt draws the image in the visualization window twice with the camera eye positioned in slightly different locations to mimic the differences in images seen by your left eye and your right eye. With the right stereo goggles, the image that you see appears to hover in 3D space within your monitor since the effect of the stereo image adds much more depth to the visualization. You can set the angle that VisIt uses to separate the cameras used to draw the images by typing a new angle into the Eye angle text field or by using the Eye angle slider.