Classic 3D

The classic 3D transformation approach creates transformation parameters using a rigorous classic 3D method.

Basically, the method works by taking the cartesian coordinates of the GNSS measured points (WGS84 ellipsoid) and comparing them with the cartesian coordinates of the local coordinates. Shifts, rotations and a scale factor are calculated, to transform from one system to another.

The classic 3D transformation approach allows you to determine a maximum of seven transformation parameters (three shifts, three rotations, and one scale factor). However you can select the parameters to be determined.

The classic 3D transformation allows the choice of two different transformation models: Bursa-Wolf or Molodensky-Badekas.

For the classic 3D transformation method, we recommend that you have at least three points for which the coordinates are known in the local system and in WGS84. It is possible to compute transformation parameters using only three common points but using four produces more redundancy and allows for residuals to be calculated.

The advantage:

The advantage:

The advantages of this method of calculating transformation parameters, are that it maintains the accuracy of the GNSS measurements and may be used over virtually any area as long as the local coordinates (including height) are accurate.

The disadvantage:

The disadvantage:

The disadvantage is, that if local grid coordinates are desired, the local ellipsoid and map projections must be known. In addition, if the local coordinates are not themselves accurate, any new points measured using GNSS, may not fit into this existing local system once transformed.
In order to obtain accurate ellipsoidal heights, the geoid separation at the measured points must be known. This may be determined from a geoid model, but many countries do not have access to an accurate local geoid model. See also Geoid Models.

Other transformation approaches:

Other transformation approaches:

Onestep

Twostep

Quick Ground