parsing a long string into chunks

I have input data of the form
<coordinates>x1,y1 x2,y2 x3,y3</coordinates>
e.g.
<coordinates>10,10 10,20 20,20</coordinates>
There can be any number of space-delimited substrings.  At present this is
parsed using substring-before and substring-after with a recursive template,
to generate a sequence of elements <Point X="10" Y="10"/> etc.
Unfortunately this can sometimes be slow for long lists (by which I mean
5000 or so x,y pairs).  In addition I have to divide up the resultant list
of elements into chunks (to avoid exceeding a limit on the number of points
in a line), although this can easily be done on a second pass (it's then a
similar problem to splitting up for a table with a given number of columns).

i.e. I want

<coordinates>x1,x2 ...

to become someething like (ignoring attributes for simplicity!)

<Polyline>
<Point><Point><Point><Point>
</Polyline>
<Polyline>
<Point><Point><Point><Point>
</Polyline>

Can anyone think of a better way, especially a way of splitting up without
the need for a second pass?  What I'd really like is a trivial way to make
xsl treat the string as a node list split at whitespace, but I suspect that
that isn't possible!

Tim


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