[linux-dvb] USALS Algorithm

Philip Prindeville philipp_subx at redfish-solutions.com
Thu Sep 8 19:19:31 CEST 2005


Hey Andrew,

Did you have a look at:

http://www.arachnoid.com/satfinder/

-Philip

Andrew Hakman wrote:

>Has anyone else noticed that the USALS algorithms being used in both
>the vdr-rotor plugin and MythTV aren't accurate for moderate distances
>away from south (or north)? Has anyone else tried to get the real
>algorithm from STAB? I've e-mailed them a few times and they seem
>reluctant to release the algorithm - they have a good system, but it's
>pretty f'in useless without the correct algorithm. What exactly are
>they trying to protect?
>
>I haven't worked out all the trig in the formula being used in vdr or
>myth, but it generates almost identical numbers (the differences are
>in the thousandths of degrees which is irrelevant anyways) to a much
>simpler algorithm I found being used in the DiseqcU plugin for ProgDVB
>which uses very simple trig, the diamater of the earth, and the height
>of the satellites to calculate the rotation angle. The further away
>from south (or north) you calculate the angle for, the more you have
>to re-correct back towards south (or north). I haven't put a lot of
>thought into it, but a first guess at the problem I think could have
>to do with the angle present at the motor shaft. If anyone else has
>also noticed this and put some thought into what might be wrong, I'd
>sure like to get this figured out.
>
>As an example, for the furthest east satellite I can see just above
>the horizon, DiseqcU and the algorithm used in vdr-rotor and myth
>gives an angle of  75.46 degrees, whereas a real USALS receiver
>configured with the same reference location and same satellite
>location gives a motor angle of 70.4 (which considering how much
>further west I have to go from 75.46 to actually get that satellite is
>probably correct).
>
>Andrew Hakman
>
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