We provide two C-routines to calculate the projection P of a point W on an ellipse aligned with the principal axes. The projection P is the point of the ellipse that is closest to W. The result is calculated with the precision of the machine.
/// set the floating point precision here:
typedef double real;
/// calculate (pX, pY), the projection of (wX, wY) on the ellipse of axes radX, radY
void projectEllipse(real* pX, real* pY,
real wX, real wY,
real radX, real radY);
/// calculate p, the projection of a 3D point w on the ellipse of axes given in rad[]
void projectEllipsoid(real p[3],
const real w[3],
const real rad[3]);