DG Kernel (ActiveX) Documentation

See also: Concepts Of 3D Graphics, View Points
Viewing Volume is the part 3D space which is currently displayed in the 3D View. Viewing Volume is a rectangular 3D box, four sides of which are orthogonal to the plane of the screen and extensions of which intersect plane of the screen at the screen edges.
This box is tapered to form a frustum in case of perspective projection. Dimensions of the Viewing Volume are expressed relative to the Eye Frame.

Reducing the Viewing Volume to contain only a particular object of the model is equivalent to zooming in on the object. Everything else will be cut off. Expanding the Viewing Volume allow to display more on the screen, which is some sort of zoom out. All Viewing transformations like Zoom, Pan Rotate, including ones performed programmatically, result in manipulations on size, position and orientation of Viewing Volume. For example, Pan (Translation) of the scene with the mouse results in shifting the viewing volume in direction opposite to the mouse movement.
Experiment with Birds Eye view to see the above elements in action: Start any sample. Click on the DGK window. Press v,b. Try rotate/pan/zoom in the main window of the sample and observe how it affects the elements of the scene.

Programmatically dimensions of the Viewing Volume can be accessed and manipulated via IView_DG.Get/SetViewingVolume(). To manipulate its orientation its is needed to manipulate IFrame_DG of the Eye Frame obtained via IView_DG.GetEyeFrame().

Dimensions of the Viewing Volume in z direction (depth coordinate) are always finite. If model falls out of the z extents of the Viewing Volume it will appear clipped at furthest (dMin) or nearest (dMax) side of the Viewing Volume. Z dimensions are important for rotations as it determines location of center of the rotation, which coincides with center of Viewing Volume.