R help - Jun 2008 - contour plot - line passing through z values

Dear all,
there is much in these forums about adding a line to a
contour/filled.contour plot, but I haven't found hints for the following. I
apologize in advance if I just missed the right one.

I'm having a standard filled.contour plot to which I want to add a line
passing through some specific z-values at some specific x, without knowing
the y coordinates. There should be a way of getting these coordinates
(within the accuracy defined by nlevels in the initial filled.contour) but
I'm not sure how to do that, particularly as filled.contour does not return
any values.

If anyone's got any idea...please help.

Many thanks
Jehol
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On 6/19/2008 12:51 PM, Jehol wrote:
> Dear all,
> there is much in these forums about adding a line to a
> contour/filled.contour plot, but I haven't found hints for the
following. I
> apologize in advance if I just missed the right one.
> 
> I'm having a standard filled.contour plot to which I want to add a line
> passing through some specific z-values at some specific x, without knowing
> the y coordinates. There should be a way of getting these coordinates
> (within the accuracy defined by nlevels in the initial filled.contour) but
> I'm not sure how to do that, particularly as filled.contour does not
return
> any values.
> 
> If anyone's got any idea...please help.
The contourLines function will return x and y values corresponding to a 
contour.  You could search that result for a segment that crosses the x 
value of interest.

Duncan Murdoch