st_ellipse: Calculate ellipse polygon

In michaeldorman/nngeo: k-Nearest Neighbor Join for Spatial Data

Calculate ellipse polygon

Description

The function calculates ellipse polygons, given centroid locations and sizing on the x and y axes.

Usage

st_ellipse(pnt, ex, ey, res = 30)

Arguments

pnt	Object of class sf or sfc (type "POINT") representing centroid locations
ex	Size along x-axis, in CRS units
ey	Size along y-axis, in CRS units
res	Number of points the ellipse polygon consists of (default 30)

Value

Object of class sfc (type "POLYGON") containing ellipse polygons

References

Based on StackOverflow answer by user fdetsch:

https://stackoverflow.com/questions/35841685/add-an-ellipse-on-raster-plot-in-r

Examples

# Sample data
dat = data.frame(
  x = c(1, 1, -1, 3, 3),
  y = c(0, -3, 2, -2, 0),
  ex = c(0.5, 2, 2, 0.3, 0.6),
  ey = c(0.5, 0.2, 1, 1, 0.3),
  stringsAsFactors = FALSE
)
dat = st_as_sf(dat, coords = c("x", "y"))
dat

# Plot 1
plot(st_geometry(dat), graticule = TRUE, axes = TRUE, main = "Input")
text(st_coordinates(dat), as.character(1:nrow(dat)), pos = 2)

# Calculate ellipses
el = st_ellipse(pnt = dat, ex = dat$ex, ey = dat$ey)

# Plot 2
plot(el, graticule = TRUE, axes = TRUE, main = "Output")
plot(st_geometry(dat), pch = 3, add = TRUE)
text(st_coordinates(dat), as.character(1:nrow(dat)), pos = 2)

michaeldorman/nngeo documentation built on April 19, 2024, 12:04 a.m.