Adding a Polygon with the polygon() Function
Syntax of the polygon() Function
The polygon() function draws a polygon defined by a series of points. Its basic syntax is:
polygon(x, y, border = NULL, col = NULL, lty = 1, lwd = 1)
- x: Numeric vector of x-coordinates for the vertices of the polygon.
- y: Numeric vector of y-coordinates for the vertices of the polygon.
- border: Color of the polygon border. (Default is NULL, meaning no border.)
- col: Color of the polygon fill. (Default is NULL, meaning no fill.)
- lty: Line type for the border. (Default is 1, solid line.)
- lwd: Line width of the border. (Default is 1.)
Basic Example: Drawing a Simple Polygon
Here’s how to create a basic polygon:
# Generate example data x <- c(2, 4, 6, 4) y <- c(2, 4, 2, 0) # Create a basic plot plot(1:10, 1:10, type = "n", main = "Basic Polygon Example") # Add a polygon polygon(x, y, border = "blue", col = "lightblue")
- x: x-coordinates of the polygon vertices.
- y: y-coordinates of the polygon vertices.
- border = “blue”: Border color of the polygon.
- col = “lightblue”: Fill color of the polygon.
Creating a Complex Polygon
You can draw polygons with more vertices for complex shapes.
Example:
# Generate coordinates for a complex polygon x <- c(1, 3, 5, 7, 6, 4) y <- c(1, 2, 1, 4, 6, 4) # Create a basic plot plot(1:10, 1:10, type = "n", main = "Complex Polygon") # Add a complex polygon polygon(x, y, border = "red", col = "yellow")
- x and y: Coordinates for the vertices of the polygon.
- border = “red”: Border color of the polygon.
- col = “yellow”: Fill color of the polygon.
Highlighting Areas
Polygons can be used to highlight specific areas on the plot.
Example:
# Generate example data x <- c(2, 4, 6, 4) y <- c(2, 4, 2, 0) # Create a basic plot plot(1:10, 1:10, type = "n", main = "Highlighted Area") # Add a polygon to highlight an area polygon(x, y, border = "blue", col = rgb(0.5, 0.5, 1, 0.5))
- rgb(0.5, 0.5, 1, 0.5): Defines a semi-transparent blue color for the polygon fill.
Adding Polygons to Existing Plots
You can add polygons to an existing plot using the polygon() function.
Example:
# Generate example data x <- 1:10 y <- x^2 # Create a plot with the data plot(x, y, main = "Polygon on Existing Plot") # Add a polygon polygon(c(3, 5, 7, 5), c(9, 25, 49, 16), border = "green", col = "lightgreen")
- c(3, 5, 7, 5): x-coordinates for the polygon vertices.
- c(9, 25, 49, 16): y-coordinates for the polygon vertices.
Using Polygons for Area Plots
Polygons can be used to create area plots or density plots.
Example:
# Generate density data x <- seq(0, 10, length.out = 100) y1 <- dnorm(x, mean = 5, sd = 1) y2 <- dnorm(x, mean = 7, sd = 1.5) # Create a density plot plot(x, y1, type = "l", col = "blue", ylim = c(0, max(y1, y2)), main = "Area Plot") # Add density areas with polygons polygon(c(x, rev(x)), c(y1, rep(0, length(x))), col = rgb(0.5, 0.5, 1, 0.5), border = NA) polygon(c(x, rev(x)), c(y2, rep(0, length(x))), col = rgb(1, 0.5, 0.5, 0.5), border = NA)
- c(x, rev(x)): x-coordinates for the polygon, doubled to close the shape.
- c(y1, rep(0, length(x))): y-coordinates for the polygon, with a line to 0 to close the shape.
- rgb(0.5, 0.5, 1, 0.5) and rgb(1, 0.5, 0.5, 0.5): Semi-transparent colors for the polygon fill.
Summary
- polygon() Function: Draws polygons on a plot.
- x: x-coordinates of the vertices.
- y: y-coordinates of the vertices.
- border: Border color.
- col: Fill color.
- lty: Line type for the border.
- lwd: Line width of the border.
- Basic Example: Drawing a simple polygon.
- Complex Polygons: Creating polygons with more vertices.
- Highlighting Areas: Using polygons to emphasize regions.
- Adding to Existing Plots: Incorporating polygons into existing plots.
- Area Plots: Creating area plots or density plots with polygons.