Clever Geek Handbook

R with color gradient

Below is a 3D curve using the R persp3d function and specifying colors.

library(rgl)

y = seq(-5,25,by=0.1)
x = seq(5,20,by=0.2)

NAs <- rep(NA, length(x)*length(y))
z <- matrix(NAs, length(x), byrow = T)
for(i in seq(1,length(x))) {
    for(j in seq(1,length(y))) {
        val = x[i] * y[j]
        z[i,j] = val
        if(z[i,j] < 0.02) {
            z[i,j] = NA
        }

    }
}

col <- rainbow(length(x))[rank(x)]

open3d()
persp3d(x,y,z,color=col,xlim=c(5,20),ylim=c(5,10),axes=T,box=F,xlab="X Axis",ylab="Y Axis",zlab="Z Axis")

And it creates this image:

enter image description here

In the current version, for a value of x 15, the color is blue, regardless of the value of z. But I would like the high z-values ​​to be dark blue, while the low z-values ​​to be blue, if that makes sense. How can I do something like this so that the color not only distinguishes the x values ​​but also the z values?

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2 answers


To do this, you have to play with HSV colors rather than RGB. It's easier for me.

See my example code below.

library(rgl)

y = seq(-5,25,by=0.1)
x = seq(5,20,by=0.2)

NAs <- rep(NA, length(x)*length(y))
z <- matrix(NAs, length(x), byrow = T)
for(i in seq(1,length(x))) {
  for(j in seq(1,length(y))) {
    val = x[i] * y[j]
    z[i,j] = val
    if(z[i,j] < 0.02) {
      z[i,j] = NA
    }

  }
}

Create a unique color for each x value.

col <- rainbow(length(x))[rank(x)]


Create a grid of colors by repeating col

length(y)

times

col2 <- matrix(rep(col,length(y)), length(x))
for(k in 1:nrow(z)) {

  row <- z[k,]
  rowCol <- col2[k,]  
  rowRGB <- col2rgb(rowCol) #convert hex colors to RGB values
  rowHSV <- rgb2hsv(rowRGB) #convert RGB values to HSV values

  row[is.na(row)] <- 0
  v <- scale(row,center=min(row), scale=max(row)-min(row)) # scale z values to 0-1

  rowHSV['s',] <- v #update s or v values by our scaled values above
  # rowHSV['v',] <- v  # try changing either saturation or value i.e. either s or v

  newRowCol <- hsv(rowHSV['h',], rowHSV['s',], rowHSV['v', ]) #convert back to hex color codes
  col2[k,] <- newRowCol #Replace back in original color grid
}

open3d()
persp3d(x,y,z,color=col2,xlim=c(5,20),ylim=c(5,10),axes=T,box=F,xlab="X Axis",ylab="Y Axis",zlab="Z Axis")

This should lead to the following. You can play around scaling the saturation or color value to get the desired "lightness" or "dark" hues.

enter image description here

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All you had to change was this one line:



library(rgl)

y = seq(-5,25,by=0.1)
x = seq(5,20,by=0.2)

NAs <- rep(NA, length(x)*length(y))
z <- matrix(NAs, length(x), byrow = T)
for(i in seq(1,length(x))) {
    for(j in seq(1,length(y))) {
        val = x[i] * y[j]
        z[i,j] = val
        if(z[i,j] < 0.02) {
            z[i,j] = NA
        }
    }
}

col <- rainbow(length(z))[rank(z)] # This line changed

open3d()
persp3d(x,y,z,color=col,xlim=c(5,20),ylim=c(5,10),axes=T,box=F,xlab="X Axis",ylab="Y Axis",zlab="Z Axis")
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