Leica GPS1200 Series Technical Reference Manual page 925

Determine Coordinate System - General
Transformation Characteristic
Twostep Principle
Positions and
heights
Use
Requirements
Description
Combines the advantages of the Onestep and the
Classic 3D transformation. It allows treating position
and height separately, but is not restricted to smaller
areas. Procedure:
1. The WGS 1984 coordinates of the common
control points are shifted closely to the local
datum using a given Classic 3D pre-transforma-
tion. This is typically a rough transformation valid
for the country of the local datum.
2. The coordinates are projected onto a preliminary
grid, but this time using the true map projection
of the local points.
3. A 2D transformation is applied, exactly as with
the Onestep transformation.
The position and height transformations are sepa-
rated.
When measurements are to be forced to tie in with
local existing control in areas larger than 10 x 10 km.
• The position is known in WGS 1984 and in the
local system for at least one point. Four points or
more are recommended in order to obtain higher
redundancy.
• Parameters of the local ellipsoid.
• Parameters of the local map projection.
GPS1200 925