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Thread Subject:
curve interpolation by parabolic blending

Subject: curve interpolation by parabolic blending

From: enprush@gmail.com

Date: 22 Jun, 2013 12:06:41

Message: 1 of 3

I'm given a set of 25 points(x,y values). I need to curve fit these points using a parabolic blending. I'm not sure how to go about it. I read that we need to take 3 points at a time to ensure a unique parabola is obtained.
I need to:
take first 3 points(1,2,3) and fit a parabola to it.
take the next 3 points (2,3,4) and do the same.
This goes on till i reach my final point. The overlapping portions of any two parabolas is linearly blend using a cubic curve.

So, this looks more like a polyfit of third order except between point 1 and 2. Am i right in continuing on with a ployfit of order 3?

Thanks

Subject: curve interpolation by parabolic blending

From: dpb

Date: 22 Jun, 2013 23:08:16

Message: 2 of 3

On 6/22/2013 7:06 AM, enprush@gmail.com wrote:
> I'm given a set of 25 points(x,y values). I need to curve fit these
> points using a parabolic blending. I'm not sure how to go about it. I
> read that we need to take 3 points at a time to ensure a unique parabola
> is obtained.
> I need to:
> take first 3 points(1,2,3) and fit a parabola to it.
> take the next 3 points (2,3,4) and do the same.
> This goes on till i reach my final point. The overlapping portions
> of any two parabolas is linearly blend using a cubic curve.
>
> So, this looks more like a polyfit of third order except between
> point 1 and 2. Am i right in continuing on with a ployfit of order 3?

Well, you can certainly find the coefficients of the quadratic at each
set of three points w/ polyfit and use polyval to evaluate it over the
range.

I don't know the details of how the blending is supposed to work so
can't suggest much on that point w/o having some reference to work from.
  A quick google turned up several references but none that weren't more
reading that had time to delve into...

--

Subject: curve interpolation by parabolic blending

From: Bruno Luong

Date: 23 Jun, 2013 07:38:07

Message: 3 of 3

enprush@gmail.com wrote in message <45c219c0-e021-4fa3-96d2-8c7b8b249c69@googlegroups.com>...

>
> So, this looks more like a polyfit of third order except between point 1 and 2. Am i right in continuing on with a ployfit of order 3?

No, order 2.

Bruno

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