Structure to define a Camera View.
Camera up vector. It should be defined so that it is perpendicular to the vector created between the camera and target position. A non-perpendicular up vector results in a view which is tilting when it is activated in the Adobe PDF Reader.
This parameter is only applicable for orthographic cameras. It specifies the part of the scene that can be visualized and inversely acts as a zoom factor with the following relationship: [zoomfactor=1/2*view_size], with view_size as the smallest size of the viewable part in the X or Y direction.
Specifies that this view should be the default view (the view used when the 3D is activated). Only one view should be defined by default.