[Numpy-discussion] Creating parallel curves

Charles R Harris charlesr.harris@gmail....
Sun Feb 12 14:37:03 CST 2012


On Sun, Feb 12, 2012 at 1:26 PM, Andrea Gavana <andrea.gavana@gmail.com>wrote:

> Charles,
>
> On 12 February 2012 21:00, Charles R Harris wrote:
> >
> >
> > On Fri, Feb 10, 2012 at 9:38 AM, Andrea Gavana <andrea.gavana@gmail.com>
> > wrote:
> >>
> >> Hi All,
> >>
> >>    my apologies for my deep ignorance about math stuff; I guess I
> >> should be able to find this out but I keep getting impossible results.
> >>
> >> Basically I have a set of x, y data (around 1,000 elements each) and I
> >> want to create 2 parallel "curves" (offset curves) to the original
> >> one; "parallel" means curves which are displaced from the base curve
> >> by a constant offset, either positive or negative, in the direction of
> >> the curve's normal. Something like this:
> >>
> >
> > Note that curves produced in this way aren't actually 'parallel' and can
> > even cross themselves.
>
> I know, my definition of "parallel" was probably not orthodox enough.
> What I am looking for is to generate 2 curves that look "graphically
> parallel enough" to the original one, and not "parallel" in the true
> mathematical sense.
>
>
You could try setting a point and 'contracting' the curve towards the
point. A point a infinity would give the usual parallel curves. There are
probably a lot of perspective like transformations that would do something
similar.

Chuck
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