all points on a 3D object are at the same distance from the camera without significant errors in the projection (compared to the full perspective model). Equation assuming focal length . Diagram To determine which screen x-coordinate corresponds to a point at multiply the point coordinates by: where is the screen x coordinate is the model x coordinate is the focal length—the axial distance from the camera center to the image plane is the subject distance. Because the camera is in 3D, the same works for the screen y-coordinate, substituting y for x in the above diagram and equation. You can use that to do clipping techniques, replacing the variables with values of the point that's are out of the FOV-angle and the point inside Camera Matrix. This technique, also known as "Inverse Camera", is a Perspective Projection Calculus with known values to calculate the last point on visible angle, projecting from the invisible point, after all needed transformations finished. See also 3D computer graphics Camera matrix Computer graphics Cross section (geometry) Cross-sectional view Curvilinear perspective Cutaway drawing Descriptive geometry Engineering drawing Exploded-view drawing Homogeneous coordinates Homography Map projection (including Cylindrical projection) Multiview projection Perspective (graphical) Plan (drawing) Technical drawing Tesseract Texture mapping Transform, clipping, and lighting Video card Viewing frustum Virtual globe References Further reading External links Creating 3D Environments from Digital Photographs 3D computer graphics 3D imaging Display devices Euclidean solid geometry Functions and mappings Graphical projections Linear algebra Projective geometry