Give a Little, Zone Tolerances

February 28, 2019

The Problem

Comp pilots fly with different makes and models of vario and can expect some error when the instrument makes its distinctive sound that the flight has flown into the turnpoint cylinder, tagging the zone. A glance at the screen can confirm this as it switches to display the distance and track to the next turnpoint.

A Workaround

To compensate the pilots for these inaccuracies, the GAP rules have some give around turnpoints. Instruments have improved over the years and the tolerance in the rules is being tightened up. The tolerance was set at half a percent of the turnpoint radius but this is reducing to a tenth of a percent or 5m, whichever is the smaller.

Aside from the tracklogs, the extract-input command from flare-timing is able to extract all the inputs it needs from the competition *.fsdb except for the Earth model used and the amount of tolerance allowed around control zones. These are supplied as command line options:

> extract-input --help
...
Give when crossing zones:
--give-fraction=NUM  How much give as a fraction, eg. 0.5% = 0.005?
--give-distance=NUM  How much give in metres?
Earth math:
-p --pythagorus         Pythagorus' method on a plane
-h --haversines         Haversines on a sphere
-v --vincenty           Vincenty's method on an ellipsoid

Borderline, Border and Line

Some pilots are cutting it fine as can be seen in these screenshots following Tyler Borradaile around the course as he tags turnpoints BUMF and WELLIN with only one fix inside the radius with the added give and no fixes inside the turnpoint cylinder zone proper.

Task map zoomed to extents

Not visible yet at this zoom, the solid fill shows the extent of the zone proper while the border line traces the zone with added give.

Zoomed in tagging BUMF

This pilot is cutting it fine again at BUMF.

Give before zone

An exit cylinder has the give border line drawn inside of the fill. A pilot flying to the edge of an exit cylinder leaves the zone with added give before they leave the zone proper.

Zoomed in tagging WELLIN

At this zoom level, we can see that the filled area of the WELLIN cylinder is not flown through but the border line drawn around the turnpoint cylinder with added give is.