  Semialgebraic splines are bivariate splines over meshes whose edges are arcs
of algebraic curves. They were first considered by Wang, Chui, and Stiller. We
compute the dimension of the space of semialgebraic splines in two extreme
cases. If the polynomials defining the edges span a three-dimensional space of
polynomials, then we compute the dimensions from the dimensions for a
corresponding rectilinear mesh. If the mesh is sufficiently generic, we give a
formula for the dimension of the spline space valid in large degree and bound
how large the degree must be for the formula to hold. We also study the
dimension of the spline space in examples which do not satisfy either extreme.
The results are derived using commutative and homological algebra.
