In bmcgaughey1/HexSampleR: Create Sample Points For Polygon(s)

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  fig.path = "man/figures/README-",
  out.width = "100%"
)

HexSampleR

The HexSampleR package is designed to facilitate the creation of sample point locations that represent a specific land area such as the area sampled by a single plot within the Forest Inventory and Analysis program of the USDA Forest Service.

Installation

HexSampleR is only available as a development version. The devtools package is required to install HexSampleR. If you have not previously used devtools, use the commented line of code to install the package. Note that this will also install several additional packages needed for devtools. If you do not want the vignette, set build_vignettes = FALSE.

You can install the development version from GitHub with:

# install.packages("devtools")
library(devtools)
devtools::install_github("bmcgaughey1/HexSampleR", build_vignettes = TRUE)

Example

This example produces a set of sample points for Snohomish County, Washington. The points represent a hexagonal grid with some random offsets. The example uses the computeCellSize() helper function to compute the cell size needed to generate the sample points given a desired sample area (6000 acres) and sampling pattern. Note that the units for cellsize will be feet since the sample area is in acres so we need to explicitly convert to meters to match the UTM projection by dividing by 3.2808.

library(sf)
#library(raster)
library(ggplot2)
library(HexSampleR)

# load a polygon representing Snohomish County Washington and reproject from longlat to UTM 10N
WASnoCo <- WASnoCo

# reproject into UTM zone 10...generatePolygonSamplePoints() won't work with data in LAT-LON
WASnoCo <- st_transform(WASnoCo, crs = 26910)

# Creates a set of sample points on a regular hexagonal grid with each point representing
# approximately 6000 acres. This is the area that corresponds to the area sampled by a single FIA plot.
# Offset the points by a random amount to produce a slightly irregular hexagonal grid.
pattern <- "hexagonal"
cellsize <- computeCellSize(6000, aunits = "acre", pattern = pattern) / 3.2808

sample_pts <- generatePolygonSamplePoints(WASnoCo
                                          , polyBuffer = cellsize / 2
                                          , pattern = pattern
                                          , gridSpacing = cellsize
                                          , IDColumnLabel = "NAME"
                                          , perturb = TRUE
                                          , perturbMultiplier = 0.1
                                          )

ggplot(WASnoCo) +
  ggtitle("Hexagonal Grid of Sample Points With Random Offset") +
  geom_sf(aes(fill = COUNTYFP), show.legend = FALSE) +
  geom_sf(data = sample_pts, colour = "black", size = 2)