6,521 research outputs found
Automatic normal orientation in point clouds of building interiors
Orienting surface normals correctly and consistently is a fundamental problem
in geometry processing. Applications such as visualization, feature detection,
and geometry reconstruction often rely on the availability of correctly
oriented normals. Many existing approaches for automatic orientation of normals
on meshes or point clouds make severe assumptions on the input data or the
topology of the underlying object which are not applicable to real-world
measurements of urban scenes. In contrast, our approach is specifically
tailored to the challenging case of unstructured indoor point cloud scans of
multi-story, multi-room buildings. We evaluate the correctness and speed of our
approach on multiple real-world point cloud datasets
Parametric Surfaces for Augmented Architecture representation
Augmented Reality (AR) represents a growing communication channel, responding to the need to expand reality with additional information, offering easy and engaging access to digital data. AR for architectural representation allows a simple interaction with 3D models, facilitating spatial understanding of complex volumes and topological relationships between parts, overcoming some limitations related to Virtual Reality. In the last decade different developments in the pipeline process have seen a significant advancement in technological and algorithmic aspects, paying less attention to 3D modeling generation. For this, the article explores the construction of basic geometries for 3D model’s generation, highlighting the relationship between geometry and topology, basic for a consistent normal distribution. Moreover, a critical evaluation about corrective paths of existing 3D models is presented, analysing a complex architectural case study, the virtual model of Villa del Verginese, an emblematic example for topological emerged problems. The final aim of the paper is to refocus attention on 3D model construction, suggesting some "good practices" useful for preventing, minimizing or correcting topological problems, extending the accessibility of AR to people engaged in architectural representation
Construction of a VC1 interpolant over triangles via edge deletion
We present a construction of a visually smooth surface which interpolates to position values and normal vectors of randomly distributed points on a 3D object. The method is local and uses quartic triangular and bicubic quadrilateral patches without splits. It heavily relies on an edge deleting algorithm which, starting from a given triangulation, derives a suitable combination of three- and four sided patches
Role of Horizons in Semiclassical Gravity: Entropy and the Area Spectrum
In any space-time, it is possible to have a family of observers who have
access to only part of the space-time manifold, because of the existence of a
horizon. We demand that \emph{physical theories in a given coordinate system
must be formulated entirely in terms of variables that an observer using that
coordinate system can access}. In the coordinate frame in which these observers
are at rest, the horizon manifests itself as a (coordinate) singularity in the
metric tensor. Regularization of this singularity removes the inaccessible
region, and leads to the following consequences: (a) The non-trivial
topological structure for the effective manifold allows one to obtain the
standard results of quantum field theory in curved space-time. (b) In case of
gravity, this principle requires that the effect of the unobserved degrees of
freedom should reduce to a boundary contribution to the
gravitational action. When the boundary is a horizon,
reduces to a single, well-defined term proportional to the area of the horizon.
Using the form of this boundary term, it is possible to obtain the full
gravitational action in the semiclassical limit. (c) This boundary term must
have a quantized spectrum with uniform spacing, , in the semiclassical limit. This, in turn, yields the
following results for semiclassical gravity: (i) The area of any one-way
membrane is quantized. (ii) The information hidden by a one-way membrane
amounts to an entropy, which is always one-fourth of the area of the membrane
in the leading order. (iii) In static space-times, the action for gravity can
be given a purely thermodynamic interpretation and the Einstein equations have
a formal similarity to laws of thermodynamics.Comment: Extends and presents the results of hep-th/0305165 in a broader
context; clarifies some conceptual issues; 24 pages; revte
Mobility of bodies in contact. I. A 2nd-order mobility index formultiple-finger grasps
Using a configuration-space approach, the paper develops a 2nd-order mobility theory for rigid bodies in contact. A major component of this theory is a coordinate invariant 2nd-order mobility index for a body, B, in frictionless contact with finger bodies A1,...A k. The index is an integer that captures the inherent mobility of B in an equilibrium grasp due to second order, or surface curvature, effects. It differentiates between grasps which are deemed equivalent by classical 1st-order theories, but are physically different. We further show that 2nd-order effects can be used to lower the effective mobility of a grasped object, and discuss implications of this result for achieving new lower bounds on the number of contacting finger bodies needed to immobilize an object. Physical interpretation and stability analysis of 2nd-order effects are taken up in the companion pape
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