More extensive results of postprocessing G12 raw data




There are two postprocessing steps. In the first one, the 8 individual static baselines were processed. The second step (adjustment) receives those results and gives us a best fit to the data.

When processing an individual baseline GeoGenius gives us three solutions. The first one is obtained using triple differences. It is quite noisy, but is quick to compute and doesn't have to solve ambiguities, serving as an starting point for more refined solutions.

Then a double difference solution is obtained, where the ambiguities are solved as real numbers, instead of integers. That is called a float double difference solution.

Finally, the software attemps to fix the integer ambiguities by basically exploring those integers close to the float ambiguity. If the set of integers that best explains the observations is significantly better than the second option, the ambiguities are considered fixed. In that case, that baseline is considered known to a few milimeters. Only in five cases (out of eight) the software could resolve the integer ambiguity.

The problem of a fixed solution is that if we choose the wrong set of integer ambiguities, the position would be wrong by an amount of one or several wavelengths (20 cm).

These were the adjusted baselines using each kind of solution:

Baseline Solution DX(mt) DY(mt) DZ(mt) SigmaDX(mm) SigmaDY(mm) SigmaDZ(mm)
MAD2-f1 Triple 4065.3656 34834.0132 -1984.1105 139.5 153.1 98.8
MAD2-f1 Double Float 4065.2902 34834.3575-1984.2004124.3149.081.4
MAD2-f1 Double Fixed 4064.9740 34834.3459 -1984.1345 469.4 167.0 384.6

You can see the complete results of the triple, double float, and double fixed solution in these adjustment reports generated by GeoGenius.

Some remarks:



In this setup we simulate a small network. Two GPS12 (in the same conditions as above) were placed 15 mt. apart. Data was logged simultaneously in two sessions (Jul 10-11). The other point of the network was the reference station MAD2. Now we had 3 simultaneous baselines: MAD2 to f1, MAD2 to f2, and f1 to f2.

After the previous experience we only considered floating solutions to the double difference equations. Here are the final adjusted results:

Baseline DX(mt) DY(mt) DZ(mt) SigmaDX(mm) SigmaDY(mm) SigmaDZ(mm)
MAD2-f1 4065.3498 34834.9477 -1983.8023 293.2 564.8 268.0
MAD2-f2 4075.7219 34843.0945 -1995.4062 292.8 564.1 267.6
f1-f2 -10.3722 -8.1468 11.6039 45.7 81.6 38.0

Again, the sigmas in the previous table correspond to a standard deviation (60% confidence level). The larger errors for the long baselines are the result of only having two sessions (instead of eight as before). You can have a look at the complete adjustment report generated by GeoGenius.

Ultima Modificación: Mon Apr 8 12:18:34 CEST 2002