# st_ellipse: Calculate ellipse polygon In michaeldorman/nngeo: k-Nearest Neighbor Join for Spatial Data

## Description

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

## Usage

 `1` ```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`:

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22``` ```# 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 June 17, 2021, 7:52 a.m.