Jim Wilson writes:
>
>Norman Vine <[EMAIL PROTECTED]> said:
>
>> Perhaps tie'ing it to the current waypoint makes sense ...... hmmm
>>
>
>Yes, but I'd probably want to wait until I was within a few
>kilometers of the "current" waypoint before switching.
or perhaps when the 'current waypoint' is closer then the
the 'current tower location'
>That would do the trick. We'd need that anyway if we wanted to do an
>approximate model of a GPS some day.
I don't understand what you mean by model a GPS
Are you are using 'GPS' to mean a 'muti-function' GPS receiver ?
If so most of the pieces are already in place.
still need a 'cross-track error' though
< untested pseudo code, off the top of my head >
using normallized geocentic representation
i.e. direction cosine form using geocentric latitude
sgdSubVec3( dir, track_start, track_end )
// simgear function
sgdClosestPointToLine( closest_pt, current_pt, track_start, dir )
// can probably skip this next step for 'short enough' tracks
sgdNormalizeVec3(closest_pt)
sgdScaleVec3(closest_pt,sea_level_radius)
sgdScaleVec3(current_pt, sea_level_radius)
sgdSubVec3(error_vec, closest_pt, current_pt)
// this should be close enough for our purposes
crosstrack_error_dist = sgdScalarProductVec3(error_vec)
Norman
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