Viewing instructions

Since it is most likely that you will be changing the viewing parameters, they will be described here. Oplot is capable of producing views in either parallel or perspective projections. The math of these viewing transformations will not be explained here; instead, the user is referred to a standard Computer Graphics text such as Foley & Van Damm. The main thing to remember is that the viewing coordinate system is left handed. That is, if x is horizontal, and y is vertical on the plotting surface, then z is pointing away from you. Thus, the front of the viewing volume, has a lower z-value than the back of the viewing volume. In the default setting, (also used in O metafiles) the position of the observer is at (0,0,-1) and the look-at point is (0,0,0).

The following oplot commands affect the viewing of the objects.

window

[uwmin uwmax vwmin vwmax]. Specify the limits of the window in the plane of projection. The default size of the window is (0, 1, 0, 1).

viewport

[uvmin uvmax vvmin vvmax]. Where on the visible area to display the contents of the window. The limits of the viewport must be given in the range [0:1]. The default size of the viewport is (0, 1, 0, 1).

view_reference_point

[x y z]. Set the view reference point (the look-at point). The default value is (0,0,0).

view_point_normal

[x y z]. Set the view plane normal. Default is (0,0,-1).

up_direction

[x y z]. Set the view-up direction. Default is (0,1,0).

parallel

[x y z]. Define the projection to be parallel, and specify the direction of the projection. The default setting is (0,0,1) and the parallel projection mode is default.

perspective

[x y z]. Define the projection to be perspective, and specify the center-of-projection (the eye point). Default is (0,0,-1). The default projection mode is parallel.

depth_cue

[on / off]. Set depth cueing on. Same as using the -z option. Default is off.

slab

[front back]. Set the slab limits.

zthick

[front back]. Set the value of the linethickness at the front and back slab limits. Only has a visible effect if depth cueing is on. Default values are front = 4.0, back = 1.0 .

front_clipping

[on / off]. Set clipping at the front slab limit on or off. Default value is off.

back_clipping

[on / off]. Set clipping at the back slab limit on or off. Default value is off.

display

[object]. Add an object to the display list. ONLY displayed objects will be visible in the plot!