The equations on this page use the following parameters which are specific to the particular projection that is being converted to or from. The correct values for different New Zealand projections can be found in the projections section.
|a||Semi-major axis of reference ellipsoid|
||Latitude of first standard parallel|
||Latitude of second standard parallel|
||Latitude of computation point|
|λ||Longitude of computation point|
|N||Northing of computation point|
|E||Easting of computation point|
The following equations are divided into three sections:
Several additional parameters need to be computed before transformations can be undertaken (e, n, F, ρ0). These parameters are constant for a projection.
m1 and m2 are obtained by evaluating m using ϕ1 and ϕ2,
t0, t1 and t2 are obtained by evaluating t using ϕ0, ϕ1, and ϕ2,
ρ0, is obtained by evaluating ρ using t0
The conversion of geographic coordinates (ϕ, λ) to projection coordinates ( N , E ) is achieved in several steps. First, determine t and ρ at the using the latitude of the computation point (ϕ) and the formulas above. Then evaluate θ at the longitude of the computation point (λ) using:
The projection northing ( N ) of the computation point is computed using:
Finally the projection easting ( E ) of the computation point is computed using:
The conversion of Lambert projection coordinates ( N , E ) to geographic coordinates ( f , l ) is achieved in several steps. First, determine N1, E1, ρ1, t1 and θ1 using the following formulas:
The latitude of the computation point needs to be computed iteratively. The first approximation is obtained from:
This initial estimate of ϕ is then substituted into:
This value of ϕ should be re-substituted into the above formula until successive values do not change. This is typically achieved after three iterations.
The longitude of the computation point (λ) is determined using: