This page explains how to convert NZMG projection coordinates ( N , E ) to their NZGD1949 geographic equivalents and vice versa.
|a||Semi-major axis of reference ellipsoid|
|Latitude of computation point|
|Longitude of computation point|
|N||Northing of computation point|
|E||Easting of computation point|
The following equations are divided into three sections:
The conversion of NZGD1949 geographic coordinates (,) to NZMG projection coordinates ( N , E ) is achieved in several steps.
The conversion requires the latitude and longitude expressed in decimal degrees (north and east are positive). The constants are provided on the NZMG page and coefficients used in these formulae are listed below.
Calculate a complex polynomial function of the complex numberusing the formula:
Express the complex number z in terms of its real and imaginary parts and calculate the northing N and easting E from x and y as:
The conversion from NZMG to latitude and longitude involves an iterative approximation to reverse step 2 above. This starts with the easting E and northing N. The steps to calculate latitude and longitude are as follows. Note that the constants and coefficients used in these formulae are listed below. Derive the complex number z as the following steps.
Determine the complex number θ as a series of approximations θ0 , θ1 , θ2 and so on. The first approximation is:
Successive approximations are obtained by applying the formula:
Two iterations of this formula will give millimetre transformation accuracy.
Expressin terms of its real and imaginary partsand calculate the latitude and longitude as follows
|Coefficient||Real Part||Imaginary Part|