Tim:
The following is probably just an historical curiosity but might be a
useful stimulant to someone.
Formation tops in one of the Arabian Gulf hydrocarbon bearing salt
domes are close to pure ellipsoidal surfaces. In early 1969 I wrote a
Fortran 4 program that solved the quadric equations using 3D
formation tops from just nine wells using a solution for simultaneous
equations. Input UTM coords then gave predicted tops anywhere else
on the structure, as confirmed by actual drilling results.
It worked well but perhaps fortunately, my life took other directions.
Regards
Malcolm
On 7 Jul 2009, at 5:58PM, Tim Wynn wrote:
> Malcolm, Deepak,
> 5 points are the minimum required to uniquely define an ellipse (see
> http link below)
>
> A few years ago I tested various ellipse fitting algorithms
> (written up
> in JSG somewhere). The 3 point analytical method I tested (DePaor
> 1988)
> is the least accurate with large axial ratios and the most susceptible
> to noise in the data. However, it is simple and fast and will work
> fine
> with good quality data and low axial ratios (<6).
>
> Regards
>
> Tim Wynn
>
>
> http://users.cs.cf.ac.uk/Paul.Rosin/resources/papers/ellipse3.pdf
>
> DePaor, D.G., 1988. Strain determination from three known stretches-an
> exact solution. Journal of Structural Geology 10, 639-642
>
>
>
>
> -----Original Message-----
> From: Tectonics & structural geology discussion list
> [mailto:[log in to unmask]] On Behalf Of Malcolm McClure
> Sent: 07 July 2009 16:43
> To: [log in to unmask]
> Subject: Re: Free Data Graphing, Animation, and Analysis Software
>
> Deepak:
> ACD systems Canvas 9.0.4 has a 3 point circle fitting option. 3
> points may not be enough to define an unique ellipse.
> Regards
> Malcolm.
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