Re: [Flightgear-devel] Helipad thresholds

[Florent R. <f.r...@fr...>]

Hi,

James Turner <ja...@fl...> wrote:

> I don’t *think* theshold.xml files add any new information to the mix,
> they were merely a way to override the base apt.data when we didn’t
> have support for custom apt.dat files in scenery.

I confirm this — except *.threshold.xml files may override runway
headings, but that would be a rather strange need[1].

Because I spent some time clearing this up due to the somewhat strange
lat/lon data in LIPX.threshold.xml, here is a comment regarding these
*.threshold.xml files (example from TerraSync's LFPG, possibly
outdated):

    <threshold>
      <lon>2.61060285</lon>
      <lat>48.99875734</lat>
      <rwy>26R</rwy>
      <hdg-deg>265.41</hdg-deg>
      <displ-m>577.0</displ-m>
      <stopw-m>0.0</stopw-m>
    </threshold>

AFAICT, and despite the <threshold> element name, the 'lat' and 'lon'
coords should indicate where the runway _end_ resides (i.e. where you
_start_ when taking off from 26R... it's called this way in the apt.dat
v1000 spec) — not the runway threshold. 'displ-m' is the distance from
that runway end to the corresponding threshold. So, changing displ-m has
no effect whatsoever on the startup position when using --runway=26R.

One thing I find strange, though, is that I can't use the built-in
launcher as in the attached screenshot in order to start above the
runway threshold: this puts me above the runway end. Maybe I use this
incorrectly?

Regards

[1] When apt.dat files are used, the forward and reciprocal headings
    are computed from the opposite runway ends pos_1 and pos_2 using
    SGGeodesy::inverse(pos_1, pos_2, heading_1, heading_2, length).

-- 
Florent