EPSG:1070

Note: These formulas have been transcribed from EPSG Guidance Note #7-2. Users are encouraged to use that document rather than the text which follows as reference because limitations in the transcription will be avoided.

The NTv2_Vel grid contains point velocities resolved into north, east, and up components.

First the three velocities at a point are interpolated within the NTv2_Vel grid using bi-linear interpolation within the source and target CRS.

Then ellipsoidal coordinates of a point at coordinate epoch t1 may be calculated at any other coordinate epoch t2 from:

[Lat(t2)] = [Lat(t1)] + (t2-t1) * [V_lat]
[Lon(t2)] = [Lon(t1)] + (t2-t1) * [V_lon]
[h(t2)] = [h(t1)] + (t2-t1) * [V_up]

where V describes the velocities of the ellipsoidal coordinates. These are given as a rate in linear units (metres per year) resolved into north, east and up components VN, VE and Vh. The north and east components are converted into latitude and longitude components by:
	V_lat = VN / (rho+h)
	V_lon = VE / [(nu+h) cos(lat)] 
where 
	rho is radius of curvature of the CRS's ellipsoid in the plane of the meridian at latitude lat 
	rho = a(1 – e^2)/(1 – e^2sin^2(lat))^3/2
	nu is radius of curvature of the ellipsoid perpendicular to the meridian at latitude lat 
	nu = a /(1 – e^2sin^2(lat))^1/2