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.