Projection
When three-dimensional graphics are displayed on a flat computer screen or printed on paper, they must be projected onto the viewing plane. A projection is a way of converting positions in 3D space into locations in the 2D viewing plane. IDL supports two types of projections—parallel and perspective—for each view.
Parallel Projections
A parallel projection projects objects in 3D space onto the 2D viewing plane along parallel rays. The figure below shows a parallel projection; note that two objects that are the same size but at different locations still appear to be the same size when projected onto the viewplane.
View objects use a parallel projection by default. To explicitly set a view object to use a parallel projection, set the PROJECTION keyword to the IDLgrView::Init method equal to 1 (or use the SetProperty method to set the projection for an exiting view object):
Perspective Projections
A perspective projection projects objects in 3D space onto the 2D viewing plane along rays that converge at the eye position. The figure below shows a perspective projection; note that objects that are farther from the eye appear smaller when projected onto the viewplane.
Set the PROJECTION keyword to the IDLgrView::Init method equal to 2 (or use the SetProperty method to set the projection for an exiting view object) to use a perspective projection:
