Poly4Sin
Description
Vertical offset computed by a polynomial of degree 4 on the sine of the latitude:
f(x) = c4 * x^4 + c3 * x^3 + c2 * x^2 + c1 * x^1 + c0 Hout = Hin + scale * f(sin(latitude))
where Hin is the vertical coordinate value in the source datum, Hout is the vertical coordinate value in the target datum and scale is the scale factor from metres to vertical units.