Mark,
Correction and clarification on my previous response:
By small angles, I meant small angle DIFFERENCES -- the series expansions work
best for small angles. The sine expansion to 3 terms is good within 1% up to
pi/2, as is the cosine expansion to 4 terms (the first term is always 1, so
it's equivalent to sine to 3 terms). Then you find yourself doing if-then
ladders for the four quadrants, i.e. sin(pi/2 < x < pi) = sin(pi - x), sin(pi
< x < 2pi) = - sin(x - pi), and so on. I haven't thought about how do to this
in fop, so this may or may not help.
-dd
"David S. Dixon" wrote:
> Mark,
>
> Well, you could do what most implementations of sine and cosine would do,
> series expansion:
>
> sin(x) = x - x^3/3! + x^5/5! - x^7/7! ...
>
> cos(x) = 1 - x^2/2! + x^4/4! - x^6/6! ...
>
> I haven't tried it, but if you avoid small angles (not a bad idea with pie
> charts, anyway) the expansion shouldn't have to include more than three
> terms, I suspect.
>
> -dd
>
> Mark wrote:
>
> > Hi folks,
> >
> > sorry for this slightly off topic post but i was hoping someone could
> > help me.
> >
> > I thought i should be able to produce a very simple xml schema for
> > generating pie charts. the idea was that I could use XSLT to transform
> > from the pie-chart schema to SVG (and then to import the SVG into FOP).
> >
> > It would be preferable to express the size of the pie chart segments as
> > percentages, but the SVG Path object requires coordinates on the
> > circumferance of a circle.
> >
> > The problem is that there don't seem to be any functions in XSLT or
> > XPath that let me find the sin() or cosine() of an angle. Am I missing
> > something? I thought I could possibly use a transform but I can't seem
> > to perform a transform in the middle of a Path.
> >
> > I finally decided that maybe if I created a table of degree-to-sin/cos
> > mappings I could somehow use the document() function to import this into
> > the stylesheet and use an index to search it (ergh) but that doesn't
> > seem to work either.
> >
> > There's little point in having a pie-chart schema if you have to do the
> > calculations yourself anyway.
> >
> > So if anyone has any suggestions .. ? I'd certainly be pleased to share
> > a pie-chart-XSLT transform if I can get it going.
> >
> > As an aside, does anyone know why SVG paths are so (IMHO) brain dead? I
> > can't believe that the elements in a path aren't XML elements, it seems
> > very strange. (Generating the paths in XSLT is going to be a bit
> > painful, even if I can get the sin() of an angle. I dont really see how
> > "M300,200 h-150 a150,150 0 1,0 150,-150 z" qualifies as XML).
> >
> > Cheers
> > Mark
> >
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