MATLAB Central Newsreader - Spline through non uniformly spaced points

Spline through non uniformly spaced points

David Doria — Wed, 07 May 2008 18:05:09 -0400

I want to do something like this:

a=axes;
set(a,'xlim',[-2 2]);
set(a,'ylim',[-2 2]);
[x y] = ginput;

%click a bunch of points

%draw a spline through the points
xx=-2:.01:2;
yy=spline(x, y, xx);

the problem seems to be that the points I have clicked are
not uniformly spaced (clearly) so i get the following:
"The data sites should be distinct."

I've used meshgrid before, but it seems to be more for
plotting 3d functions.. i'm not sure how to "snap" these
coordinates to a grid without giving them some kind of "z"
value.

Any suggestions?

Thanks,

Dave

Re: Spline through non uniformly spaced points

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) — Wed, 07 May 2008 18:13:41 -0400

In article <fvsr0k$n1h$1@fred.mathworks.com>,
David Doria <daviddoria@gmail.com> wrote:
>I want to do something like this:

>a=axes;
>set(a,'xlim',[-2 2]);
>set(a,'ylim',[-2 2]);
>[x y] = ginput;

>%click a bunch of points

>%draw a spline through the points
>xx=-2:.01:2;
>yy=spline(x, y, xx);

>the problem seems to be that the points I have clicked are
>not uniformly spaced (clearly) so i get the following:
>"The data sites should be distinct."

Not having the points uniformly spaced does not cause that problem.
What -would- cause that problem is clicking the same location twice,
such as if you were to close a curve. The message is telling you
that all of the point pairs must be unique.
--
"And that's the way it is." -- Walter Cronkite

Re: Spline through non uniformly spaced points

David Doria — Wed, 07 May 2008 18:45:06 -0400

ah ok , great - I don't think I had clicked exactly in the
same point, I think two points just had the same X
coordinate - is this indeed the reason for that error?