Showing papers on "Perspective (geometry) published in 1988"

An Error Analysis For Surface Orientation From Vanishing Points

Abstract: There are many cases in which perspective information can be used to derive three-dimensional spatial information about objects from their two-dimensional images. There are established algorithms for estimating the direction of lines and the orientation of surfaces based on their projections onto the image plane. Given two parallel lines on a plane, their projections onto the viewing plane intersect at a vanishing point, which provides a constraint on the orientation of the plane. Two such independent constraints define a vanishing line, and thereby determine the orientation of the plane uniquely. In order to effectively recover surface orientations via lines extracted from the image, it is necessary to put bounds on the errors while applying these constraints. Our approach involves representing line directions and surface normal vectors as points on a Gaussian sphere and computing the error bounds as regions on the sphere. Multiple constraints are combined by intersecting the corresponding regions. The starting point for computing the error bounds is an estimate of the accuracy of the lines which are extracted from the image. A mathematical analysis of the imaging geometry is used to propagate these errors to vanishing points, vanishing lines, and surface orientations. In addition, constraints based on a priori knowledge can be introduced to improve the accuracy. Some experimental results are presented to illustrate this.

Photographs of flat impressions and their projective symmetry

Abstract: Evidence photographs of two-dimensional impressions, taken without aligning the camera focal plane parallel to the plane of the impression, should not be rejected because they suffer from perspective deformation. A consideration of projective symmetry offers a possible solution to the problem of identification with such photographs of questioned and control impressions which requires no knowledge of the exact size and shape of the original impressions.

Camera, especially CCD-camera, for the recognition of an object, the surveying of an object or the like

Abstract: The invention relates to a CCD-camera, in which the sensor is mounted so as to be pivotable about a transverse axis running parallel to the central plane of the lens, so that the image plane can always be adjusted in such a way that the object plane, lens plane and image plane intersect, as a result of which a CCD-camera can be realised in which distortions of perspective may be compensated.

A Modular Network Perspective Model vs. Vectorial Models

Abstract: The author presents a model of projective perspective named Modular Network and analyzes how it differs from vectorial methods, primarily in regard to its geometric conception based on tri-dimensional models. He discusses the principles of modular scale as well as the characteristics of the plane onto which the image is projected in perspective and the importance of taking the focal distance into account so as to control the projection according to a determined aperture of the visual field. The usage of the author's modular scale, whose design is based on the determination of the scale of depth, is shown in a graphical perspective.