Leica GPS1200 Series Technical Reference Manual page 927

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Requirements to deter-

mine a transformation

Determine Coordinate System - General

Transformation Characteristic

Disadvantage

With one common control point, it is still possible to calculate a Classic 3D transformation,

as long as the rotations and the scale parameter are fixed. Such a transformation fits

perfectly in the vicinity of the common control point, but is degraded by the distance from that

point, because neither the orientation of the local reference frame nor any scale factor within

the local datum can be taken into account.

To determine a transformation it is necessary to have common control points whose posi-

tions are known in both WGS 1984 coordinates and local coordinates. The more points that

are common between datums the more accurately the transformation parameters can be

The first step of a Twostep transformation avoids

any distortions due to the fact that the preliminary

grid coordinates are built on a different ellipsoid

than the local points. The second step ensures

that the influence of the scale factor of the map

projection is equally taken into account before the

final 2D transformation is computed.

The local ellipsoid must be known.

The map projection must be known.

A pre-transformation must be known. A null trans-

formation can be used.

In order to obtain accurate ellipsoidal heights, the

geoid separation at the measured points must be

known. This may be determined from a geoid

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