A Simple Method for Implicitizing Rational Curves and Surfaces
Résumé
This paper presents a simple method for converting rational parametric equations of curves and surfaces into implicit equations. The method proceeds by writing out the implicit polynomial $F$ of estimated degree with indeterminate coefficients $u_i$, substituting the rational expressions of the given parametric curve or surface into $F$ to yield a rational expression $g/h$ in the parameter $s$ (or $s$ and $t$), equating the coefficients of $g$ with respect to $s$ (and $t$) to 0 to generate a sparse, partially triangular system of linear equations in $u_i$ with constant coefficients, and finally solving the linear system for $u_i$. If a nontrivial solution is found, then an implicit polynomial is obtained; otherwise, one repeats the same process by increasing the degree of $F$. Our experiments show that this simple method is efficient. It performs particularly well in the presence of base points and may detect the dependency of parameters incidentally.