GTRA Transformation of GPS-data from WGS84 into the control point system
Columns | format | contents/explanation |
|---|---|---|
1-4 | A4 | GTRA (format free) |
| 7I1 | Transformation key with 7 digits. Every digit is either Zero or One. Exactly 7 digits have to be indicated. |
| 3F | X0, Y0, Z0: Shift components of the transformation |
| 3F | Φ, Ω, Κ: Rotational angles in gon of the transformation |
| F | S: Scale factor of the transformation |
It is supposed, that the GPS-coordinates had already been transformed from the geocentric WGS84-system into the coordinate system, where the control points are also defined. Nevertheless the transformation might be only an approximation, as the geoid transformation parameters might be not known exactly for these reference points, e.g. due to geo-undulations. For this reason BINGO allows to determine new transformation parameters simultaneously in the bundle block adjustment. Then there can only remain small rotations and shifts.
The transformation key with 7 digits decides which transformation parameters are introduced as unknowns or as fix values. 1110001 means e.g. that the three coordinate shifts X0, Y0, Z0 and the scale S are unknowns in the adjustment. Contrarily Φ, Ω and Κ are fix values. The indication of values for the transformation parameters is optional. For missing values zero will be used instead (respectively one for the scale).
For very small networks or for single strips, the parameters Φ and Ω should not be introduced as unknowns, as they cannot be estimated in this case.
This transformation is not intended for use together with shift and drift parameters; in such cases it should only be used with extreme caution.