2 distincts stations in one adjustement

by Micha ⌂, Bad Vilbel, Monday, November 23, 2020, 15:57 (62 days ago) @ Antoine Chabert

Hello Antoine,

Thanks, we analyse that you differentiate "stations" and "new points" in 2 distincts groups in "new points" ?
Is it a good practice ? does it change something in the adjustment ? Should we insert it in our project ?

No, such separation has no effect on the results. However, I'm not part of your project, so I have to re-organise the project to get a better impression. It was just for me. Sorry for confusion.

All the direction are calculated between the CD, with always the same formula. We oriented it from the north. An excel file is attached where the calculation is available.
But I am not sure to understand why you disabled these observations. Why did you do this ? Indeed, the project had a particular geometry; with strains between the CD points : in directions sets ; zenith angles & slope distance.

Whereas a direction is a un-orientated observation, a direction angle is defined between a station and two target points. For that reason, a single direction makes not sens because it only contributes to the unknown orientation. However, if really all directions between the CD points are derived within the same datum, you can enable the group. In this case, all directions contribute to the same unknown orientation redundantly. As already mention, I was not sure about this fact and, therefore, disabled such pseudo-observations.

Theorically, we can not disactivate once parameters : directions sets and you can not always adjust the network.
But in practice, we can adjust the network... How does it work ? Where the strains in directions sets are usefull ? They seems to be useless...

Are you referring to the unknown orientation? This parameter describes the discrepancies of the north-direction of your frame and the zero-direction of the total-station (angle-encoder). See above, a direction is not an (direction) angle. A direction of 100 gon (90 °) does not imply that the target point is located in the east.

"I would also suggest to use some kind of trimmed coordinates to avoid numerical instabilities, i.e., reducing all X/Y/Z coordinates to their average values. "
You mean that we should do a preprocessing : approximation values (CTRL+M) ? before do the command "adjust network" ?

No, just averaging the coordinates in Excel, for instance, and reduce each coordinate by the mean. Currently, the network extent is about 500 m x 500 m. If, for example, the origin is set to 0/0, the maximal coordinate becomes 500/500. Small coordinate values will increase the numerical stability because of the 64 bit limit of double values.

Yes we know this low quality of our networks but in case of AMTS monitoring, we did not find a solution to make redundancy.

Okay, it was just a note, but if you keep it in mind - no problem.

regards
Micha

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applied-geodesy.org - OpenSource Least-Squares Adjustment Software for Geodetic Sciences


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