# comp.graphics.algorithms

## Subject: Re: Fast search of closest point on a fix 3D polyline

Dave,

You showed me a good example.

So lets say that:
- the polyline represents the centerline of a path that your car should
follow
- the input point is a point of the car or in front of the car (not too
far)

In this scenario, situations like the one you described are not likely
to happen (I think).
Of course I need to have a robust solution meaning that in certain
unlucky cases (don't know what they are now) I HAVE to do safe search
without taking into account the position of the previous input point.

Thanks

Jonni

Dave Eberly ha scritto:

> "Jonni" wrote in message
>
> > I guess that somehow I can do that taking into account that the
> > position of the input point does not change
> > too much between 2 searches and so the closest point of a new search is
> > likely to be close to the one of the previous search.
>
> Without any knowledge of specific properties of your
> polyline, the closeness of two input points does not
> is a circle (for simplicity of the argument) with center
> (0,0) and radius 1. The first input point is (e,0) for
> a small positive e. The closest point is (1,0). The
> second input point is (-e,0) but the closest point is
> now (-1,0), so searching near (1,0) will not quickly
> find the closest point.
>
> --
> Dave Eberly
> http://www.geometrictools.com