[R] Creating "Envelope" around a plot

[WRAY NICHOLAS]

Hi  I am plotting various strands of information, and I want to create an
"envelope" around each line, so that the locus of the envelope is the boundary
points no more than a fixed maximum distance from the plotted line, a bit like
drawing a larger rectangle with paralle sides and curved compass corners around
a smaller rectangle.  Obviously I can work out how to do this in code
(eventually) but I suspect it would take me a while and i was wondering whether
there was some R function which I don't know about which creates sets of of
points at a given maximal distance

the lines are simple vectors, ie like this noddy example

veca<-c(4,3,6,5,7,3,2,3,3,6,8,7)
plot(veca,type="l",lwd=2)

then I want to plot the locus of the boundary of all points no more than (say) 1
unit from the line  I imagine that one would have to provide a larger set of
interpolated points between the actual points of veca, but I can do that no
problem

I'd be grateful if anyone out there in the R-ethervoid has any ideas

Thanks, Nick Wray
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