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rscatter-plotraster

Adding a line to a scatter plot in R

I have a scatter plot of two raster images. What I need is to create a triangle around the scatter plot. So far what I have it 

minveg <- quantile(veg, 0.01, na.rm=TRUE)
mintemp <- quantile(temps, 0.01, na.rm=TRUE)
plot(veg, temps, xlab='veg', ylab='temp')
abline(h=mintemp, v=minveg)

This give me the following image

enter image description here

What I need is a third line that goes along the scatter plot and completes the triangle with the other two lines. I'm sure I could add an equation just looking at it and fit my best idea but I have to do this for hundreds of images and was looking for a more automated way to do it. Any suggestions are helpful. Thanks!

Solution

  • You can use quantile regression for this.

     library(quantreg)

 # example data
 set.seed(0)
 x = rnorm(1000)
 y = rnorm(1000) - x


 minx <- quantile(x, 0.01, na.rm=TRUE)
 miny <- quantile(y, 0.01, na.rm=TRUE)
 plot(x,y, xlim=c(-6,6), ylim=c(-6,6))
 abline(h=minx, v=miny, col='red') 
 abline(rq(y ~ x, tau=.99), col='blue')