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From: Nina Hinchy on 10 Mar 2010 11:58
Hi,

I'm trying to create a spline from a set of points which form a closed contour and calculate the tangents and normals to the curve at its break points. I've got some code which does most of the work, but I don't understand where its failing.

My code just comprises of a few lines, please have a look:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

spline = cscvn(I1_coords);
break_coords = fnval(spline, spline.breaks);
xPts = break_coords(1,:);
yPts= break_coords(2,:);

pts = fnval(spline, xPts);
tangent = fnval(fnder(spline), xPts);

quiver(pts(1,:), pts(2,:), tangent(1,:), tangent(2,:));

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

The output looks like this:

http://www.freeimagehosting.net/image.php?511fccf2ec.png

If anyone could tell me why only some of the tangent vectors have been drawn and also why 'tangent =fnval(fnder(spline), xPts);' returns two values (I don't understand how this represents the tangent slope) I would really appreciate it.

Thanks for your help,
N.
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