1,857 research outputs found
Constrained modification of the cubic trigonometric BĆ©zier curve with two shape parameters
A new type of cubic trigonometric BĆ©zier curve has been introduced in
[1]. This trigonometric curve has two global shape parameters Ī» and Āµ. We
give a lower boundary to the shape parameters where the curve has lost the
variation diminishing property. In this paper the relationship of the two shape
parameters and their geometric eļ¬ect on the curve is discussed. These shape
parameters are independent and we prove that their geometric eļ¬ect on the
curve is linear. Because of the independence constrained modiļ¬cation is not
unequivocal and it raises a number of problems which are also studied. These
issues are generalized for surfaces with four shape parameters. We show that
the geometric eļ¬ect of the shape parameters on the surface is parabolic.
Keywords: trigonometric curve, spline curve, constrained modiļ¬catio
A survey of partial differential equations in geometric design
YesComputer aided geometric design is an area
where the improvement of surface generation techniques
is an everlasting demand since faster and more accurate
geometric models are required. Traditional methods
for generating surfaces were initially mainly based
upon interpolation algorithms. Recently, partial differential
equations (PDE) were introduced as a valuable
tool for geometric modelling since they offer a number
of features from which these areas can benefit. This work
summarises the uses given to PDE surfaces as a surface
generation technique togethe
High-order adaptive methods for computing invariant manifolds of maps
The author presents efficient and accurate numerical methods for computing invariant manifolds of maps which arise in the study of dynamical systems. In order to decrease the number of points needed to compute a given curve/surface, he proposes using higher-order interpolation/approximation techniques from geometric modeling. He uses BĀ“ezier curves/triangles, fundamental objects in curve/surface design, to create adaptive methods. The methods are based on tolerance conditions derived from properties of BĀ“ezier curves/triangles. The author develops and tests the methods for an ordinary parametric curve; then he adapts these methods to invariant manifolds of planar maps. Next, he develops and tests the method for parametric surfaces and then he adapts this method to invariant manifolds of three-dimensional maps
Subdivision surface fitting to a dense mesh using ridges and umbilics
Fitting a sparse surface to approximate vast dense data is of interest for many applications: reverse engineering, recognition and compression, etc. The present work provides an approach to fit a Loop subdivision surface to a dense triangular mesh of arbitrary topology, whilst preserving and aligning the original features. The natural ridge-joined connectivity of umbilics and ridge-crossings is used as the connectivity of the control mesh for subdivision, so that the edges follow salient features on the surface. Furthermore, the chosen features and connectivity characterise the overall shape of the original mesh, since ridges capture extreme principal curvatures and ridges start and end at umbilics. A metric of Hausdorff distance including curvature vectors is proposed and implemented in a distance transform algorithm to construct the connectivity. Ridge-colour matching is introduced as a criterion for edge flipping to improve feature alignment. Several examples are provided to demonstrate the feature-preserving capability of the proposed approach
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