Bloss spiral

An approximation to the clothoid spiral where the transition angle θ:

• θ = l^3/(R*L^2) – l^4/(2*R*L^3)

where l is the current length along the spiral, R is the radius at the end of the spiral, and L is the total length of the spiral.

This gives:

• X = L – L^3/(43.8261*R^2) + L^5/(3696.63*R^4)
• Y = (3*L^2)/(20*R) – L^4/(363.175*R^3)

where Y is the total offset from the tangent , X is the total distance along the tangent, R is the radius at the end of the spiral, and L is the total length of the spiral.