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Subject: Re: [office] chart:interpolation

On Wed, 2011-11-02 at 15:36 -0600, Andreas J. Guelzow wrote:
> On Wed, 2011-11-02 at 14:43 -0600, Andreas J. Guelzow wrote:
> > On Wed, 2011-11-02 at 14:19 -0600, Patrick Durusau wrote:
> > > 2) Are these all that we want to add? If there are others and we think 
> > > there is user demand for them, let's add them now if possible. So we 
> > > don't have to return to this attribute.
> > 
> > I am planning to provide further definition (Those provided by
> > libgoffice, ie. the ones are available in Gnumeric.) It would be good to
> > have somebody from some other implementations to see what they are
> > really doing.
> > 
> > Adding these 4, may also flush out further suggestions in the first
> > public review of these changes. 
> Sorry, I confused interpolations with trend lines. At this time I am not
> planning to suggest to add further interpolations.

I wasn't as confused as I thought. A small bug in the current
development version of Gnumeric hid some of the interpolation methods
implemented there.

So I will be proposing a few more methods:

 * Cubic spline interpolation with parabolic limits.
 * Cubic spline interpolation with cubic limits.
 * Cubic spline interpolation with fixed derivatives at both ends.

Rather than adding more attribute values to the chart:interpolation
attribute, I believe it would be cleaner (and more in the spirit of the
already existing chart:spline-* attribute) to use secondary attributes
chart:spline-limits, chart:spline-limits-start, chart:spline-limits-end
that would modify the cubic-spline interpolation already provided in ODF

Gnumeric also provides:
* Closed Bezier cubic spline interpolation.
Since this is not really a proper "interpolation" method, I am not sure
this would be appropriately added here unless other implementations
provided a similarly closed interpolation.

Andreas J. Guelzow, PhD, FTICA
Concordia University College of Alberta

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