Start Line Maths

Goodmorning,

I'm trying to use the lowest calculation overhead to figure out distance and time remaining to a start line, with saved end points a and b.

What i know is present position which coild be anywhere on 1 side of the start line, including off the ends, current speed and track

Distance to either of the end points, and also the track of the actual start line and distance of the start line

What i thought of doing was displaying the vmg at a tangent to the start line ( pythagorus) unless distance to furthest point is greater than distance of start line, in which case its vmg direcyly to the nearest start point..... thoughts?

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dpawlyk over 5 years ago

Calculate the distance from the position to both ends of the start line and to the point on the orthogonal line from the position the start line. Pick the smallest of the three distances.

Travis.ConnectIQ over 5 years ago

https://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line

Nick over 5 years ago

Ok , I managed to get all of it done in about 80 lines of code.

I ended up using a " rule" if you are further away from either start line ends, than what the length of the start line ( kind of outside it and heading towards an end, then It would use distance and time remaining to the nearest end.

If you were in the middle somewhere ( less than a start line length from both ends ), i calculated the distance Tangental to the start line ( nearest point, measured the current tangental velocity component towards it and also calculated the required tangental velocity component as a cue so you can compare required with actual.

took me all day ! but finally it's working in the Sim.

thanks for the advice - now to see what disaster awaits porting it over to the watch, :)

9256409 over 5 years ago in reply to Travis.ConnectIQ

That appears to define the distance from a point to an infinitely long line.

This might be more useful: https://stackoverflow.com/questions/849211/shortest-distance-between-a-point-and-a-line-segment

Nick over 5 years ago in reply to 9256409

That one is pretty much what I did but without the end bits. To complicate the matter I had to correct the maths based on which hemisphere and East vs West longitude also. But tested on the watch and it works great so far.. Time to release the new version of my App!.