Rotor angle prediction in advance

[bjorgan]

Currently sends (AZ,EL) at the time the position of the satellite is (AZ,EL), which makes the antenna always lag behind (subject to TLE precision), with a bias depending on the update rate and the speed of the satellite (will probably not be more than something slightly below 1 degree).

One simple fix is to predict the angles for rotor control at an advance time. If the advance time is more than the time the rotator takes to rotate to this angle and the advance time is less than or equal to the time until the next position update, the position will be correct at least once during this period, and the mean difference between expected angle and actual angle is no longer biased.

Depending on relation between rate limit, satellite speed, rotor speed and the advance time difference, this might result in just stepping with the angle being correct only at exactly one point in time, but at least not biased stepping, as is done right now. Should investigate whether it is possible to enable more smooth operation, utilizing rotor precision and speed, and whether there is any point to it.