EUROGRAPHICS ’99 / P. Brunet and R. Scopigno (Guest Editors) Volume 18 (1999), Number 3 Creating Architectural Models from Images David Liebowitz, Antonio Criminisi and Andrew Zisserman Visual Geometry Group, Department of Engineering Science, University of Oxford, Oxford, UK {dl,criminis,az}@robots.ox.ac.uk Abstract We present methods for creating 3D graphical models of scenes from a limited numbers of images, i.e. one or two, in situations where no scene co-ordinate measurements are available. The methods employ constraints available from geometric relationships that are common in architectural scenes — such as parallelism and orthogonality — together with constraints available from the camera. In particular, by using the circular points of a plane simple, linear algorithms are given for computing plane rectification, plane orientation and camera calibration from a single image. Examples of image based 3D modelling are given for both single images and image pairs. 1. Introduction The task of reconstructing objects such as buildings from photographs is receiving increased attention in the effort to create models of valuable architectural sites. We are address- ing here the key case where it is not possible to make mea- surements of features of a scene to allow reconstruction — for example cases where buildings are destroyed and only archive images are available. In the absence of direct mea- surement we wish to exploit geometric characteristics such as the parallelism and orthogonality of lines and planes. Such relationships are plentiful in manmade structures, and often provide sufficient information to produce realistic re- constructions. The techniques presented here are aimed at metric recon- struction; correct representation of angles and length ratios, but not of absolute scale. This level of reconstruction is pre- cisely that required for a graphical 3D model where the ab- solute pose (rotation and translation) and scale are not neces- sary for visualization. Computation of global scale provides no theoretical difficulty, but requires knowledge of a single length measurement in the scene. Part of the novelty of the work lies in the direct applica- tion of ideas from projective geometry 21 , such as the circular points. It will be seen that this allows simple linear equa- tions to be formulated, and avoids the non-linear constraints which typically arise in these types of applications when the orthogonality properties of rotation matrices are used. It also enables constraints from the scene and camera to be com- bined effortlessly when computing reconstructions, allowing the efficient use of all the available information. We present methods to: metric rectify individual planes, compute relative perpendicular distances from partially rec- tified planes, calibrate cameras and reconstruct piecewise planar objects from a single view. We also present a method of metric rectifying 3D reconstructions from two views. These techniques allow architectural models to be built and rendered from single images in a similar manner to the photogrammetric techniques of Debevec et al. 7 . However, in the Debevec system multiple images are necessary, scene measurements are required to position the cameras, and the camera internal calibration must be known. These are not needed here. We use several vanishing points for scene mod- elling from single images, and are therefore extending the work of Horry et al. 15 , where a single vanishing point is used. The single view techniques are complementary to re- construction methods applicable to multiple images, such as an image sequence acquired by a video camera when walk- ing around a building 1 24 26 . In section 2 we begin with a description of planar rec- tification from single view scene constraints. Section 3 de- scribes 3D modelling when one plane is partially rectified. This is followed by methods of camera calibration, in sec- tion 4. Calibration is relevant in its own right and also as an aid to the single view reconstruction of structures such as buildings, which is detailed in section 5. We briefly dis- cuss metric reconstruction from two views using vanishing c The Eurographics Association and Blackwell Publishers 1999. Published by Blackwell Publishers, 108 Cowley Road, Oxford OX4 1JF, UK and 350 Main Street, Malden, MA 02148, USA.