This paper describes a practical application of the spatial triangulation procedure in a digital photogrammetric system with images acquired by a non-metric camera. Image orientation and stereoscopic restitution were performed by means the Geosoft-GDS digital system with an aerial triangulation module which implements the DLT analytical approach necessary for non-metric images. For this purpose, a slide series of the Udine Castle front were taken by an Olympus reflex camera with an equivalent focal length of 90 mm and a shot distance of 65 m. 51 points on the building (not identified in advance) have been topographically surveyed with an sqm of about 3 mm, later divided into three groups (A, B and C) of 17 points each, so that 3 alternate independent samples of control points are made.
Three experiments were conducted by computing the simultaneous image orientation starting from every single group and from other 10 tie points. Therefore all 51 points were photogram¬metrically restituted and the obtained coordinates were compared to those obtained topographically, assumed as reference values. The obtained results show an interesting system accuracy, either in absolute sense (planimetric sqm of about 1 cm) or in relative one (by taking into account the range camera-object) in excellent agreement with the test theoretical accuracy.
