Rick,

I see a couple errors in my code ... you will need to attach the MASS
package for the eqscplot() function and that function's first arguments
should be any coordinates, I use (1, 1)

library(jpeg)
library(MASS)
# download image from internet for use in example
# http://www.tootsie.com/wallpaper/wp_concord2_1344x1008.jpg
img <- readJPEG("c:/temp/wp_concord2_1344x1008.jpg")
# define location of two yellow gumballs, could use locator() to get these
coordinates
px.x <- c(172, 576)
px.y <- c(433, 657)
# set up plot
par(xaxs="i", yaxs="i")
eqscplot(1, 1, type="n", xlim=c(0, 1334), ylim=c(0, 1008))
# add image
rasterImage(img, 0, 0, 1334, 1008)
# add line connecting two yellow gumballs
lines(px.x, px.y, lwd=5, col="yellow")

Jean



On Mon, Oct 28, 2013 at 4:12 AM, Rick Turner <rickturner@btconnect.com>wrote:

> I forgot to mention that I get an error from your code - the 'lines()'
> command fails with the error 'object px.x not found'.  I am not sure why
> (yet) but need to dig into it... sigh.
>
> Rick
>
>

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