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OFF-THE-SHELF CLOSE-RANGE PHOTOGRAMMETRIC SOFTWARE FOR CULTURAL HERITAGE DOCUMENTATION AT STONEHENGE

This paper is a summary of a student internship with English Heritage's Photogrammetric Unit. During this placement affordable solutions for heritage close-range photogrammetric measurement were examined. Topcon's Image Surveying Station PI-3000 photogrammetric software was used on a project to record carvings found on one of the stones at Stonehenge. Analysis of this carving (and others) is essential in order to understand Stonehenge's history as well as to help to conserve its condition. An original survey of this carving was carried out in 1967 (Atkinson, 1968) providing context against which this survey using PI-3000 could be compared to in the future. In preparation for this work a comparison of camera calibration techniques (using PI-3000 and PhotoModeler) was carried out. Creating a 3D model using the photogrammetric method based on a bundle adjustment requires knowledge of camera calibration parameters. Photogrammetric camera calibration parameters allow for the recovery of the central perspective bundle. They can be determined during a self calibration process if using appropriate software. It was decided to assess the camera calibration provided by PI-3000. Therefore, to test the software, a Canon IXUS 900Ti was calibrated using PI-3000 and PhotoModeler. The paper presents the results of these calibrations and compares the two software packages. PI-3000 was then used to document a single carving found on inner face of the 53 rd stone of Stonehenge. The outcome could be compared with the survey performed in 1967. Around ten images were collected with a calibrated Cannon A640 camera. Scale was introduced to the scene using a ruler laid against the stone. PI-3000 was then used to produce a meshed surface of the carving. Results will be presented. The paper concludes that off-the-shelf photogrammetric equipment and software could be utilized in commercial projects to provide heritage recording. However, principles of close range photogrammetry still needed to be understood in order to produce high quality results.