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Subject: Re: [office] chart:interpolation
On Mon, 2011-11-07 at 13:36 -0700, Patrick Durusau wrote: > Andreas, > > On 11/03/2011 04:36 PM, Andreas J. Guelzow wrote: > > <snip> > > > I wasn't as confused as I thought. > > That's always a comfort. ;-) > > > 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 > > 1.2. > > To confirm before you enter them in JIRA: > > chart:spline-limits > > chart:spline-limits-start > > chart:spline-limits-end > > Valuetype = ? Until the proposal is finished, I don't think I am sure which value types will be the most appropriate. chart:spline-limits-start/end are probably going to be expressions that shall evaluate to a number. chart-spline-limits will be some kind of enumeration. > > What do we have to reference in current 20:26? (I know it is probably > obvious but we should not simply say: apply to 20:26 as appropriate.) In 20.26 this would not affect the text for the step functions but it will change the limit handling in the cubic splines. > > On prose for these attributes, let's avoid: > > > 20.51 If the chart:spline-resolution attribute has value 1 this > > is identical to the chart:interpolation attribute value none. > > That is really awkward and I am not altogether sure it is necessary. I am not sure why that sentence is preceded by "20.51" (that's the section describing "chart:spline-resolution".) The purpose of that sentence is intended to provide a definition for b-spline (and cubic-spline) in the case of the resolution 1. Of course one could omit that sentence since in the case resolution == 1 the described method yields the same result as using method none. > Unless we mean to bind the value of chart:spline-resolution to > chart:interpolation? That is if chart:spline-resolution > 1 then > chart:interpolation *cannot* have the value of none? > > > 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. > > > > Other implementers? Anyone? My comment wasn't quite correct. The description of the cubic-spline method reflects the implementation in LibreOffice/OpenOffice: If the first and last data point are the same then a closed cubic spline is created otherwise an open one. In Gnumeric one would need to specify whether one wants a closed or open cubic spline, there is no automatic guessing of whether a closed or open spline is used. (Note that an "open" spline with the first and last data point the same simply has a corner at that point. This is something that may be expected by a user and provides a continuous behaviour as the last and first data point approach each other.) So I will make a proposal that allows both behaviours to be specified. Andreas -- Andreas J. Guelzow, PhD, FTICA Concordia University College of Alberta
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