[metapost] (no subject)

[Laurence Finston]

On Mon, 17 Jan 2005, Honza Prachar wrote:

>
> Do you have any idea how to do a tangent to path p from point z.
>

You'll have to be more specific.  For example, a `path' can
represent a straight line segment, in which case the problem
reduces to determining whether `z' lies on that line.  It could
also represent an `ellipse', so if `z' is located at one of the
corners of the surrounding rectangle, it lies on two tangents
to the `path'.  I believe you can use `directiontimes' to
determine the direction in which a `path' is
travelling at a given "time", but I don't have my _METAFONTbook_
handy, so I can't look this up.  Since MF's `paths' are Bezier curves,
and the latter can approximate a very wide range of curves, you could
potentially have a very large number of tangents.  This sounds
like a job for Larry Siebenmann and Boguslaw Jackowski!

Laurence Finston
http:/www.gnu.org/software/3dldf/LDF.html