将等高线图限制为不同图的凸包

Question

I have a contour plot in R. I would like to only show the region of this plot that lies inside the convex hull of a set of data-points from a different plot. All the region outside of this area should be blank (white).

A reproducible example:

Here's the plot that produces the convex hull:

ExampleValues <- matrix(sample(1:30), ncol = 2)
plot(ExampleValues)
hpts <- chull(ExampleValues)
hpts <- c(hpts, hpts[1])
lines(ExampleValues[hpts, ])

Here's a different plot showing some contours (here using the package ' plotly '):

ContourPlotData <- data.frame(X = sample(1:50), Y = sample(1:50), Z = sample(1:100))
plot_ly(x = ContourPlotData$X, y = ContourPlotData$Y, z = ContourPlotData$Z, type = "contour")

Now, I want to show only the part of the contour plot that is within the values specified by the convex hull from the first plot, and set all of the rest of the contour plot to be white. I would be very grateful if anyone has any advice as to how to do this.

Answer 1

A possibile solution in based on shapes inside layout . See here for details.
An SVG path for the convex hull and the plot area must be defined. The sintax is defined here .

set.seed(1)
df1 <- matrix(sample(15:46), ncol = 2)
hpts <- chull(df1)
hpts <- c(hpts, hpts[1])
df2 <- volcano

####
# Build the SVG path used in 'shapes'
####
nc <- ncol(df2)
nr <- nrow(df2)

# Plot area
xbox <- c(1, 1, nc, nc, 1)-1
ybox <- c(1, nr, nr, 1, 1)-1

# Convex hull
xpoly <- c(df1[hpts, 1])
ypoly <- c(df1[hpts, 2])

# SVG path (see https://www.w3schools.com/graphics/svg_path.asp )
pathbox <- c(paste0(xbox,",",ybox))
pathbox <- paste0(c("M",rep("L",length(pathbox)-1)), pathbox)

pathpoly <- c(paste0(xpoly,",",ypoly))
pathpoly <- paste0(c("M",rep("L",length(pathpoly)-1)), pathpoly)

SVGpath <- paste(c(pathpoly, pathbox,"Z"),collapse=" ")

library(plotly)
plot_ly(z=~df2, type = "contour") %>%
layout(shapes = list(
       list(type='path', path=SVGpath, fillcolor="white")
))