In arc2r/book: All things R Spatial or A guide to spatial R for Recovering ArcGIS Users

Sampling Toolset {#sampling}

knitr::include_graphics("images/network/Data Management_Sampling.png")

For this chapter, you will need the following R Packages:

library(sf)
library(arc2r)
library(ggplot2)
library(dplyr)

Generate Tessellation {#sampling-generatetessallation}

Generate Tessellation tool in ArcGIS pro is used for generating a tessellated grid of regular polygon features. The generated output is covering a certain extent that usually represents the respective extent of another spatial feature. The aforementioned operation in R is possible using the function st_make_grid of the sf package. Below we present an example of how we can create a tesselated grid covering the spatial extent of the canton of Zurich in Switzerland.

# Reading the simple feature object that depicts all the cantons of the country of Switzerland
data("kantonsgebiet")

# Selecting only the geometric extent of the canton of Zurich
zh <- filter(kantonsgebiet, NAME == "Zürich")

# Plotting the selected area
ggplot(zh) + geom_sf() + coord_sf(datum = 2056)

# Creating a tessellated grid of hexagons using the st_make_grid() function. 
g <- st_make_grid(zh, square = FALSE) # square = TRUE creates as expected a tesselation of squares

# Plotting the generated output over the spatial representation of the canton of Zurich
ggplot() + geom_sf(data = zh, fill = "red") +
  geom_sf(data = g, alpha = 0.3, color = "black") + coord_sf(datum = 2056) +
  ggtitle("Tesselated grid within the Canton of Zürich") +
  theme(plot.title = element_text(hjust = 0.5), text = element_text(size=9))

Create Random Points {#sampling-randompoints}

Create Random Points tool in ArcGIS pro serves as a very straightforward way of generating randomly distributed points within an extent window, inside polygon features, on point features, or along line features. In R the respective operation can be again achieved using one of the functions provided by the sf package. Below we present how we can perform this operation with the function st_sample().

# Create random points (1000) within the spatial extent of the Canton of Zurich
sample <- st_sample(zh, size = 1000)

# Plotting the randomly generated points over the spatial feature that
# represents the canton of Zurich
ggplot() + geom_sf(data = zh) + 
  geom_sf(data = sample) +
  coord_sf(datum = 2056) + 
  ggtitle("1000 random points witihn the Canton of Zurich") 

Generate Points Along Lines {#sampling-pointsalonglines}

data("mountainBikes_routes")

line1 <- mountainBikes_routes[1,]
pointsOnLine1 <- st_line_sample(line1,50, type = "random")


plot(st_geometry(line1))
plot(pointsOnLine1, add = TRUE, pch = 20, col = "red")

arc2r/book documentation built on March 5, 2021, 2:10 p.m.