[metapost] Re: tangent
Honza Prachar
pracj3am at mbox.troja.mff.cuni.cz
Mon Jan 17 23:54:23 CET 2005
On Mon, 17 Jan 2005, Boguslaw Jackowski wrote:
> This foretells troubles:
>
> 1. The solution need not to be unique; but this problem can be (iteratively
> or recursively ;) overcome.
> 2. What about singular points, such as the point 1/2 of p, where
> p=(0,0) .. controls (1,1) and (0,1) .. (1,0) ? You should rather
> accept the path going through z and such a peak, although the
> path direction is singular there, namely: (0,0).
>
> HP> I found solution using loop to determine right point, where tangent
> HP> and curve have same direction. But I do not believe it is the
> HP> simpliest solution.
>
> Could you present your solution?
z is in origin, curve is concave (see picture)


 * * *
 * *
 * *
 * *
 *
path curve;
pair a;
numeric intersect, dir, t, delta;
delta:=0.1;
t:=length curve;
forever:
a := point t of curve;
a  (intersect,0) = whatever * (direction t of curve);
exitif (intersect<0);
t := t  delta;
intersect := whatever;
endfor
draw origin  (1.5[origin,a]);

`Honza` Prachar
More information about the metapost
mailing list