[R] plotting over a raster image with control over location and orientation

[Greg Snow]

For base plotting functions (not grid) then you may be interested in
the updateusr function in the TeachingDemos package.  If you can find
the current coordinates of 2 points on the 1st plot (the background
image) that are not in the same horizontal or vertical line (use the
locator function if nothing else) and you know what you would like the
coordinates of the 2 points to be, then you just call updateusr with
the current coordinates and the desired coordinates and it resets them
for you so that you can add to the current plot with lines or other
low level functions.

On Fri, Aug 21, 2015 at 8:30 AM, ravi <rv15i at yahoo.se> wrote:
> Hi,I would like to get some help in plotting over an image. I have a png image over which I would like to have a plot. I would like to be able to control the location, area and orientation of the plot on the image.
> I have taken help from the following references :http://journal.r-project.org/archive/2011-1/RJournal_2011-1_Murrell.pdfhttp://stackoverflow.com/questions/12918367/in-r-how-to-plot-with-a-png-as-background
> In order to give a reproducible example, I set up my image with the help of some code from the the first reference above.
>
> #Setting up the initial example raster image
> x <- y <- seq(-4*pi, 4*pi, len=27)
> r <- sqrt(outer(x^2, y^2, "+"))
> z <- cos(r^2)*exp(-r/6)
> image <- (z - min(z))/diff(range(z))
> step <- diff(x)[1]
> xrange <- range(x) + c(-step/2, step/2)
> yrange <- range(y) + c(-step/2, step/2)
> plot(x, y, ann=FALSE,xlim=xrange, ylim=yrange,xaxs="i", yaxs="i")
> rasterImage(image,xrange[1], yrange[1],xrange[2], yrange[2],interpolate=FALSE)
>
> # the explanation of my problem starts here
> # First, I want to mark out a particular line
> lines(c(10,10.5),c(-10.5,10),col="red",lwd=2)
> #In my problem, I have to locate these points graphically from the image
> calpoints <- locator(n=2,type='p',pch=4,col='blue',lwd=2)
> # this gives the line corresponding to the x-axis for my overlay plot
> # I don't want the red line on my plot
> #the red line plotted earlier is just to show the example location
> newOrigin<-calpoints[1]
> xLimit<-calpoints[2]#xlimit marks the limit of the x-axis on the image# on this new line as the x-axis, I want to make a new plot# the y-axis should be perpendicular to the x-axis. I would like to be able to specify the width of coverage over the image#example
> xx<-1:10
> yy<-xx^2
> plot(xx,yy,xlim=range(xx),ylim=range(yy),col="blue",type="b",xlab="x",ylab="square of x")
> # I would prefer to have the image more transparent just under the x and y labels and axis labelsThanks, Ravi
>
>
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>
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> and provide commented, minimal, self-contained, reproducible code.



-- 
Gregory (Greg) L. Snow Ph.D.
538280 at gmail.com