GapAnalysis (version 1.0.2)

Gbuffer: @title Geodesic buffer around points (long, lat) using metric radius EXTRACTED FROM GEOBUFFER R PACKAGE

Description

Allows the possibility of creating geodesic buffers when the radius is given in metric units. A geodesic buffer is not affected by the distortions introduced by projected coordinate systems. This function is a wrapper of `geosphere::destPoint()`.

Usage

Gbuffer(
  xy,
  dist_m,
  step_dg = 10,
  crs = "+proj=longlat +ellps=WGS84 +datum=WGS84",
  output = "sp",
  ...
)

Arguments

xy

One of the following: `SpatialPoints`, `SpatialPointsDataFrame`, points as `sf`, or two columns `matrix`, `data.frame` or `data.table`, with the first column containing unprojected longitudes and the second containing unprojected latitudes of your points around which you desire buffers.

dist_m

Distance in meters passed as `d` to `geosphere::destPoint()`. The distance must be a numeric vector. Its length must be either 1 (assuming you want the same buffer radius for all points in `xy`), or the total number of points you have in `xy` (assuming you want a different buffer radius for each point).

step_dg

Step of bearings (directions) in degrees. Must be numeric of length 1. Defaults to 10. Dictates the point density of the buffer edge, therefore the buffer's shape. For example, the maximum allowed value of 120 corresponds to 360/120 = 3 points on a circle, which will form a buffer as an equilateral triangle. For more circle-like shaped buffers, use a smaller step like 10, 5 dg or even smaller. However, the smaller the step, the more computational intensive the operations are. The smallest allowed value is 1 dg.

crs

Character string of projection arguments. Defaults to `"+proj=longlat +ellps=WGS84 +datum=WGS84"`. The CRS must be the one corresponding to your points/coordinates. If you are unsure, then could be a safe bet to try the default value. For more details see `?sp::CRS`.

output

Dictates the type of output. Character vector with one of the following values: `"sp"`, `"sf"`, `"data.table"` or `"data.frame"`. Defaults to `"sp"`. If indicates a spatial object (`"sp"` or `"sf"`), then it returns the buffers as polygons around the given points. If indicates a table object (`"data.table"` or `"data.frame"`), then it returns the points that constitute the buffers as a 3 columns `data.table` or `data.frame`: `lon`, `lat`, `id`, where `id` is the id of each point in `xy`. This can be useful for plotting with `ggplot2`.

...

Additional arguments passed to `geosphere::destPoint()`, like `a` and `f`.

Value

Depending on the value given to `output` (see above).

References

This function is a wrapper of `geosphere::destPoint()`. See also [Euclidean and Geodesic Buffering in R](https://gis.stackexchange.com/questions/250389/euclidean-and-geodesic-buffering-in-r) on gis.stackexchange. Also check [Understanding Geodesic Buffering](https://www.esri.com/news/arcuser/0111/geodesic.html).

Examples

# NOT RUN {
bucharest_500km <- Gbuffer(xy = data.frame(lon = 26.101390,
                                                 lat = 44.427764),
                                 dist_m = 500*10^3,
                                 output = "sp")
# }