
Biconic surface
The biconic surface is an asymmetric surface that has indpendent curvature and conic constant in each of the x and y directions. The sag of the biconic surface is given by the following equation

In the x-direction (y=0) the sag is a conic with curvature cx and conic constant kx. In the y-direction (x=0) the sag is a conic with curvature cy and conic constant ky.
The y curvature and conic constant are specified on the surface table of the surface data editor. The x curvature and conic constant are specified on the parameters table.
Parameters
- Rx
- Radius of curvature in the x direction, equal to 1/cx
- kx
- Conic constant in the x direction
By setting one of the curvature parameters to zero, a cylindrical surface results.
The shape of a conic is given by the following table:
k>0 | ε>1 | oblate ellipse |
k=0 | ε=1 | circle |
-1<k<0 | 0<ε<1 | prolate ellipse |
k =-1 | ε=0 | parabola |
k<-1 | ε<0 | hyperbola |