Skip to documentation
BRL-CAD
DocumentationAll documentsEnglish

PERSPECTIVE(nged)

NAME

perspective - get or set the view perspective angle

On this page

SYNOPSIS

perspective
perspective angle

DESCRIPTION

The perspective command gets or sets the perspective (field-of-view) angle for the current view.

  • No arguments: Returns the current value of gv_perspective as a floating-point number. A value of 0 (or any value ≤ SMALL_FASTF) indicates orthographic (parallel) projection.

  • One argument angle: Sets gv_perspective to the given value (in degrees). The behavior depends on the magnitude of the angle:

    • If angle > SMALL_FASTF (i.e. a positive, non-trivial value): A perspective projection matrix is constructed via persp_mat with aspect ratio 1.0, near clip at 0.01, and far clip at 1×1010. This matrix is stored in gv_pmat and the view is updated via bv_update.

    • If angle ≤ SMALL_FASTF (zero or negative): The perspective matrix gv_pmat is reset to the identity matrix, effectively switching to orthographic projection.

Typical useful perspective angles range from about 15° (narrow, telephoto-like) to 90° (wide, distorted). Values above 90° produce strongly distorted views. Setting the angle to 0 disables perspective entirely.

EXAMPLES

Example 1. Query the current perspective angle

mged> perspective

Returns the current perspective angle, e.g. 0 when orthographic projection is active.

Example 2. Enable a standard perspective view

mged> perspective 45

Sets the field of view to 45°. Objects farther from the viewer will appear smaller relative to nearby objects.

Example 3. Use a narrow telephoto-style perspective

mged> perspective 15

Sets a narrow 15° field of view, compressing depth and making distant objects appear proportionally larger.

Example 4. Disable perspective (return to orthographic)

mged> perspective 0

Resets gv_pmat to the identity matrix, switching the view back to orthographic (parallel) projection.

AUTHOR

BRL-CAD Team

BUG REPORTS

Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org