[6489] in s-news-athena
modified image() function
daemon@ATHENA.MIT.EDU (Pierre Kleiber)
Wed Feb 22 18:10:42 1995
Date: Wed, 22 Feb 95 14:41:54 PST
From: pierre@pooh.UCSD.EDU (Pierre Kleiber)
To: s-news@utstat.toronto.edu
Cc: pierre@pooh.UCSD.EDU
Reply-To: pkleiber@UCSD.EDU
I think I posted an approximation of the following yesterday,
but it seems to have evaporated. Apologies for any duplicates:
Last week I asked S-news whether anyone might have implemented a
modification of image() such that it would color a specified
subarea (e.g. a polygon) within each cell of the image() plot.
In absence of any replies, I put together the following first
stab at it:
polyimage <- function(x, y, z, zlim=range(z), sax=c(0,0,1,1), say=c(0,1,1,0))
{
cscale <- .999*nrow(xgetrgb("polygons"))/(zlim[2]-zlim[1])
for(i in 1:(length(x)-1)) {
for(j in 1:(length(y)-1)) {
color <- floor((z[i,j]-zlim[1])*cscale)+1
xp <- x[i] + (x[i+1]- x[i])*sax
yp <- y[j] + (y[j+1]- y[j])*say
polygon(xp,yp,border=F,col=color)
}
}
}
This works, although it uses the polygon colors rather than the
image colors. There are several obvious improvements, well
within my capabilities, that, aside from the polygon feature,
would make it act more like image(). It's great problem, however,
is lack of speed, and I am stymied at doing anything about that.
I suppose the best strategy would be to modify the image() source code,
which I don't have access to. I'd like advice from any of the S
gurus out there as to whether it's feasible to get ahold of the
image() source code and conduct such a project, or whether I should
just beg the folks at StatSci or ATT in hopes that the modification
I'm seeking might appear in a new revision somewhere down the road.
Cheers,
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Pierre Kleiber, Ph.D., Fishery Scientist Email: pkleiber@ucsd.edu
National Marine Fisheries Service Tel: 619 546 7076
Box 271, La Jolla, CA 92037-1508 Fax: 619 546 7003
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