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Vision based technique for photorealistic 3D reconstruction of historical items Vladimir A. Knyaz, Sergey Yu. Zheltov State Research Institute for Aviation System (GosNIIAS) Victorenko str., 7, Moscow, 125319, RUSSIA tel: 7-095-157-9205, fax: 7-095-788-6894 E-Mail: knyaz@gosniias.msk.ru Abstract Virtual reality approach creates background for creating virtual museums, virtual sites of the past and virtual worlds of the past. To fulfill such a virtual environment with virtual historical items one has a need for an accurate and productive mean for generating adequate 3D models of historical objects. The paper presents photogrammetry system, which realized vision-based technique for photorealistic 3D reconstruction of historical items. As usual historical items are objects of complex form, which can not be reconstructed basing on single stereo pair. So the proposed technique of 3D reconstruction is based on object image acquisition in stripe structural light while object rotating around vertical axis. A set of cameras is used for whole surface reconstruction. The 3D coordinate calculating is performed in suggestions that the plane of projected structural light and the rotation axis of turntable are known. The system developed includes three CCD cameras, Pentium personal computer equipped with frame grabbers, structural light projector and PC-controlled turntable. Metric characteristics of reconstructed 3D models are obtained by special system calibration technique providing estimation of all important system geometry parameters. After system calibration the 3D-reconstruction process performed automatically including image acquisition in structural light at every angle position of turntable. For accurate texture generation a set of object images in shadow-free light is acquired. The photorealistic texture is generated as a set of orthophotos on appropriate 3D model fragment. The developed methods and algorithms are realized in original Windows 9X software. Introduction Virtual reality applications and Internet communication make it possible remote exploring of virtual 3D model instead of real objects. An appearance of virtual museums provides the possibility for remote tourism, sites seeing and also for remote study and exploration of historical artifacts. Also they demand for precise and automated system for generating 3D models of historical items like the system described in (Chikatsu, 1997). The requirements to virtual models for purposes of study and exploration are higher that for virtual tourism 3D models because explorer can has a need for measuring some geometric characteristics of object and for some additional visual information. So such a 3D model has to provide metric geometry characteristics and photorealistic texture for adequate interpretation. The aim of presented work is to develop an automated mean for metric textured 3D reconstruction for such complex spatial objects as historical artifacts. The method of 3D reconstruction is based on object image acquisition in stripe structural light while object rotating around vertical axis. Because of impossibility of viewing all surface points from single camera while object rotating, three cameras are used for image acquisition. This number is the minimum sensor quantity needed for whole surface reconstruction. The 3D coordinate calculating is performed in suggestions that the plane of projected structural light and the rotation axis of turntable are known. After system calibration this technique provides automated obtaining of all object 3D coordinates in single coordinate system and acquiring appropriate set of images for photorealistic texturing. System Outline Chosen 3D reconstruction approach determines the following system configuration (Fig. 1a.):
Three Panasonic WV-CP610 CCD video cameras output composite video signal of high resolution (about 450000 pixels) which is converted into three 768x576-pixel BMP images used for image processing and 3D measurements. Cameras are located so that left camera is used for reconstruction and texturing of right part of the object, right camera is used for reconstruction and texturing of left part of the object and the upper camera is used for reconstruction and texturing of the upper part of the object. Two frame grabbers provide simultaneous real-time image acquisition from three cameras. Also frame grabber supports real time image processing for stripe line recognition and its sub-pixel image coordinate measurement. PC-controlled turntable provides rotation of the object for the given angle. The minimum angle step is 0.2°, the accuracy of positioning is 1¢. Structured light projector produces object lighting in form of contrast line, the turntable rotation axis being approximately in the plane of light. To acquire shadow-free images for texture generation three lamps are located around the object. The switching between shadow-free and structured light is performed by program. The exterior view of 3D-reconstruction system is shown in the Fig. 1b. The developed software provides the complete technology of 3D-model reconstruction. It supports:
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