Оригинальный текст - Английский - In the case of an orthographic parallel...

In the case of an orthographic parallel projection, the view volume is al-ready a rectangular parallelepiped. As we have seen in Section 12-3,obliquepro-jechon view volumes are converted to a rectangular parallelepiped by the shear- ing operation, and perspective view volumes are converted, in general, with a combination shear-scale transformation.