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Subject: Re: Downsampling with fixed intervals
Date: Mon, 10 Nov 2008 16:09:02 +0000 (UTC)
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Did you get some code to do this Wolfgang? I am trying to do something fairly similar so would be interested in seeing how you did it if so. 


"Wolfgang Schwanghart" <schwanghart@googlemail.com> wrote in message <gbdbse$kh9$1@fred.mathworks.com>...
> Thanks for your reply, John. I think, I'll try it your way. I just wanted to be sure that something like this is not already available and I'd waste time on something others could do better.
> 
> Best regards,
> Wolfgang
> 
> > 
> > No, you will not find anything that does this
> > explicitly, although one could write it without
> > too severe mental anguish.
> > 
> > Assume that you have a curve defined by a
> > sequence of points in the (x,y) plane. The
> > curve may be piecewise linear, or it may be
> > a parametric spline, defined in terms of a
> > piecewise linear arclength along the curve.
> > 
> > Start at the beginning of the curve. Find the
> > (first) intersection of your curve and a circle
> > with center at the start point. Step along
> > said curve, solving a sequence of root
> > finding problems along the way.
> > 
> > You might use the intersections tool, written
> > by Doug Schwarz and on the file exchange.
> > It will require you to define the initial curve
> > as a piecewise linear one, and then to
> > approximate your circle using a piecewise
> > linear, polygonal approximation to a circle.
> > But doing so will then be a very fast way to
> > solve your problem.
> > 
> > The only issue that you must deal with,
> > regardless of how you choose to solve the
> > problem, is if the coastline is so tightly
> > convoluted that these convolutions are
> > smaller than the length of your ruler. But
> > in that case, it just means that your ruler
> > is way too long for this problem.
> > 
> > HTH,
> > John