Search results for "Geometry"
showing 10 items of 4487 documents
A numerical simulation scheme for the albedo of city street canyons
1985
A numerical scheme is described for the calculation of effective albedo values of long city street canyons. The method is based on a generalization of the radiation model for inclined surfaces recently presented by Bruhl and Zdunkowski (1983). Calculated albedo values are compared with Aida's (1982) experimentally determined results. It is found that experiment and theory are in reasonable and in some cases in excellent agreement. Additional results obtained by varying the geometry of the street canyon as well as the surface reflectivities are shown to demonstrate the versatility of the calculation scheme.
The solvent-excluding surface as a descriptor of ionic channels: Gramicidin-A
1998
Abstract We have set out a methodology for checking the performance of the methods used to compute the Solvent-Excluding Surface. The method consists of computing the area of the Solvent-Excluding Surface of a model of channel, with a fixed pore size, for several values of the solvent radius. The graphical representation of the value of the area versus the radius of the solvent sphere shows a sharp change just at the radius of the pore. With this model we may analyze the ability of each method to describe small changes of the surface. We made the study with GEPOL93, older versions of GEPOL and MSDOT. The study is applied to a natural protein channel, as is Gramicidin-A, showing that this ty…
GEPOL: An improved description of molecular surfaces II. Computing the molecular area and volume
1991
The algorithm used by the program GEPOL for a finer description of molecular surface (for a fast calculation of molecular area and volume and for an efficient selection of sampling points) is presented in detail. Different types of surfaces such as van der Waals and Richard's molecular surfaces can be computed. As we described in the first article (J.L. Pascual-Ahuir and E. Silla, J. Comp. Chem., 11, 1047(1990)), GEPOL begins by building a set of spherical surfaces which fill the space which is not solvent accessible. In this second article, a triangular tessellation approach to select the parts of these spherical surfaces which form the molecular surface is described. By using a data coded…
Geometric contacts of surfaces immersed in Rn, n⩾5
2009
Abstract We study the extrinsic geometry of surfaces immersed in R n , n ⩾ 5 , by analyzing their contacts with different standard geometrical models, such as hyperplanes and hyperspheres. We investigate the relation between different types of contact and the properties of the curvature ellipses at each point. In particular, we focalize our attention on the hyperspheres having contacts of corank two with the surface. This leads in a natural way to the concept of umbilical focus and umbilic curvature.
Bézier surfaces of minimal area
2002
There are minimal surfaces admitting a Bezier form. We study the properties that the associated net of control points must satisfy. We show that in the bicubical case all minimal surfaces are, up to an affine transformation, pieces of the Enneper's surface.
Two View Line-Based Motion and Structure Estimation for Planar Scenes
2012
We present an algorithm for reconstruction of piece-wise planar scenes from only two views and based on minimum line correspondences. We first recover camera rotation by matching vanishing points based on the methods already exist in the literature and then recover the camera translation by searching among a family of hypothesized planes passing through one line. Unlike algorithms based on line segments, the presented algorithm does not require an overlap between two line segments or more that one line correspon- dence across more than two views to recover the translation and achieves the goal by exploiting photometric constraints of the surface around the line. Experimental results on real…
From A Medial Surface To A Mesh
2012
Medial surfaces are well-known and interesting surface skeletons. As such, they can describe the topology and the geometry of a 3D closed object. The link between an object and its medial surface is also intuitively understood by people. We want to exploit such skeletons to use them in applications like shape creation and shape deformation. For this purpose, we need to define medial surfaces as Shape Representation Models (SRMs). One of the very first task of a SRM is to offer a visualization of the shape it describes. However, achieving this with a medial surface remains a challenging problem. In this paper, we propose a method to build a mesh that approximates an object only described by …
Geometric Properties of the 3D Spine Curve
2003
Through a 3D reconstruction of the human back surface using structured light techniques, we study the properties of spine curve by means of a set of parameters related to measures commonly applied in medicine. In this way, descriptors for measuring the abnormalities in the projections of the front and sagittal planes can be computed. We build the spine curve in 3D and analyse the behaviour of the Frenet frame when along the curve the deformation processes in idiophatic scoliosis appear.
Registration of moving surfaces by means of one-shot laser projection
2005
The acquisition of three-dimensional models of a given surface is a very interesting subject in computer vision. Most of techniques are based on the use of laser range finders coupled to a mechanical system that scans the surface. These techniques lacks of accuracy in the presence of vibrations or non-controlled surface motion because of the misalignments between the acquired images. In this paper, we propose a new one-shot pattern which benefits from the use of registration techniques to recover a whole surface in the presence of non-controlled motion.
Curvilinear constraints for free form deformations on subdivision surfaces
2010
This paper presents a method to deform a subdivision surface with curvilinear constraints. It combines an intuitive free form deformation with a Loop subdivision algorithm. The main advantage of this method of deformation is that it uses only vertices of an object and satisfies the geometrical constraints provided by the user. It permits us to control the final shape of the deformed object, defining the range (i.e. the impact) of the deformation before applying it. The deformation takes into account the Loop properties to follow the subdivision scheme, allowing the user to fix some curvilinear constraints at the subdivision level he works on and to render the final object at the level he wa…