Definition

The unique point common to the plane of a PHOTOGRAPH, its PRINCIPAL PLANE, and the plane of an assumed truly VERTICAL PHOTOGRAPH taken from the same CAMERA STATION and having an equal PRINCIPAL DISTAN­CE. The point of intersection on a PHOTOGRAPH of the true PRINCIPAL LINE and the ISOMETRIC PARALLEL. The point on a PHOTOGRAPH intersected by the bisector of the angle between the PLUMB LINE and the photo­graph perpendicular. The isocentre is significant because it is the centre of radiation for DISPLACE­MENTS of IMAGES caused by TILT.