Hi Everyone
We are working on a project and the goal is to find a curve's function. While working on Nurbs, I figured out that we can define it with Control points, weight and Knots. OK! So the question pops up! Is there any mathematical equation for Nurbs?? I Put the points, weights and knots in the equation and get the curve? Afterall Nurbs modeling is based on mathematics so perhaps we can have its equation for research.
I found this paper related to my question
https://www.cs.ubc.ca/~heidrich/Papers/CHAMONIX.96.pdf
Fitting Uncertain Data with NURBS
Fitting of uncertain data, that is, tting of data points
that are subject to some error, has important applications for example
in statistics and for the evaluation of results from physical experiments.
Fitting in these problem domains is usually achieved with polynomial
approximation, which involves the minimization of an error at discrete
data points. Norms typically used for this minimization include the l1, l2
and l1 norms, which are chosen depending on the problem domain and
the expected type of error on the data points.
In this paper we describe how the l1 and l1 norms can be applied
to integral and rational B-spline tting as a linear programming problem.
This allows for the use of B-splines and NURBS for the tting of uncertain
data.
Fitting Uncertain Data with NURBS
David Rutten
Sort of, nurbs curves are polynomial piece-wise curves. So (as I understand) the shape of the span between two knots is governed by three polynomial equations {f(t)=x, f(t)=y, f(t)=z}, where t is the curve parameter.
The exact formulation of the functions depends on the control-points positions, the weights and the degree.
Sep 24, 2015
Parametric House
Thanks David
So there is a parametric equation for each span!? Unfortunately, I'm looking for a single equation for a specific arch so I guess going for Nurbs is not a good choice. Perhaps Genetic programming is the best solutionĀ for finding the equation.
Sep 24, 2015