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st: Smoothing/Spline and momentum


From   Dan Weitzenfeld <dan.weitzenfeld@emsense.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Smoothing/Spline and momentum
Date   Tue, 3 Feb 2009 15:01:10 -0800

Hi Folks,

I have data consisting of X,Y coordinates of a moving object, sampled
at an unfortunately low sampling rate.  I'm therefore trying to
approximate location in the intervals between sampling points using
some combination of interpolation and smoothing or splining.
I have tried a bunch of methods (see below), but I'm having difficulty
meeting my two goals:
1) the interpolated trajectory should always go through the sampled
points (they are sampled without error, so I feel like I should hit
them)
2) the interpolated trajectory should look like a moving object with momentum
     a.  the trajectory should be somewhat smooth, what I would call
"sports car smooth"
     b.  velocity when entering a curve is taken into account  - a
faster entry means a later, deeper apex

So far, I have tried:
-spline-
-rcspline-
-lowess-
-smooth-

I am wondering if anyone has any tips or package recommendations for
solving this fun problem.
Best,
Dan
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