Re: [Flightgear-devel] Helipad thresholds

[James T. <ja...@fl...>]

> On 19 Jul 2023, at 13:17, Florent Rougon <f.r...@fr...> wrote:
> 
>> We could add a startup option which is ‘at the threshold’ but again my
>> understanding, received from other more-aviation-trained people than myself,
>> is that displaced thresholds are about landings; for takeoffs you can always
>> use the full paved area as we describe it. (Maybe there is some concept of a
>> ‘displaced start position’ but we don’t encode it anywhere right now)
> 
> Er, but in my screenshot, you can see that I was starting in-air, so
> that was sort-of-an-approach (using the ufo). So, I got the impression
> that the launcher “on approach” location lets one choose the distance
> from runway end rather than runway threshold, which is contrary to what
> is displayed next to the spin box. Maybe I am mistaken?

Oh good point. That should indeed be reflected in the in-air starts, both in the launcher pictorial diagram and actually when starting. This likely means some bug fixes in :

- AirportDigaram.cxx, around line 396 of update(), the on-runway point should be threshold() and not geod(), and the distance computation should be from the threshold, not ‘starting from 0’ which is the paved area

- positioninit.cxx, runwayStartPos() might need an inAir flag so the call to pointOnCenterline can be offset again by the displaced threshold for in-air starts.

All of this is for runways, not helipads of course :)

Kind regards,
James