Computing the cable tensions from the sag surveys.

oct 2020
general steps to compute tension
Details of how it was done
Where the code is located


      Each telescope cable hangs between two connection points in a catenary curve.  The  sag  of the cable comes  from  the  cable weight and gravity. As the tension in the cable increases, the sag gets smaller.  By fitting a catenary to the cable curve we can compute the tension in the cable.

The general steps  to compute the tension from the sag surveys

Details of how the tension was computed

Collecting  the data

     The leica p50 laser scanner is used to collect the data. It scans an area that includes the cables. We typically collect between 5 and 90 million points for each set of cables scanned.
After the collecting the data some leica software is get the 3d points into a .las file that can  be read  by the processing programs. These leica programs run on windows.

Idl software.

    Idl routines have been written to input the .las files and compute the tensions. The major processing steps are:

Inputting the data

Localizing the cables:

    Most of this code is trying to exclude points that don't belong to the cable. findcables() tries to select points around the cables and reducing the # of points to a manageable number (typically going from 64e6 to around 2e5 points. preproccable() then does a more in depth attempt at selecting the points for each cable.

Fitting a catenary and computing the tension.

Where the code is located