# geos_measures: Compute geometric measurements In sf: Simple Features for R

 geos_measures R Documentation

## Compute geometric measurements

### Description

Compute Euclidian or great circle distance between pairs of geometries; compute, the area or the length of a set of geometries.

### Usage

```st_area(x, ...)

## S3 method for class 'sfc'
st_area(x, ...)

st_length(x, ...)

st_distance(
x,
y,
...,
dist_fun,
by_element = FALSE,
which = ifelse(isTRUE(st_is_longlat(x)), "Great Circle", "Euclidean"),
par = 0,
tolerance = 0
)
```

### Arguments

 `x` object of class `sf`, `sfc` or `sfg` `...` passed on to s2_distance or s2_distance_matrix `y` object of class `sf`, `sfc` or `sfg`, defaults to `x` `dist_fun` deprecated `by_element` logical; if `TRUE`, return a vector with distance between the first elements of `x` and `y`, the second, etc. if `FALSE`, return the dense matrix with all pairwise distances. `which` character; for Cartesian coordinates only: one of `Euclidean`, `Hausdorff` or `Frechet`; for geodetic coordinates, great circle distances are computed; see details `par` for `which` equal to `Hausdorff` or `Frechet`, optionally use a value between 0 and 1 to densify the geometry `tolerance` ignored if `st_is_longlat(x)` is `FALSE`; otherwise, if set to a positive value, the first distance smaller than `tolerance` will be returned, and true distance may be smaller; this may speed up computation. In meters, or a `units` object convertible to meters.

### Details

great circle distance calculations use by default spherical distances (s2_distance or s2_distance_matrix); if `sf_use_s2()` is `FALSE`, ellipsoidal distances are computed using st_geod_distance which uses function `geod_inverse` from GeographicLib (part of PROJ); see Karney, Charles FF, 2013, Algorithms for geodesics, Journal of Geodesy 87(1), 43–55

### Value

If the coordinate reference system of `x` was set, these functions return values with unit of measurement; see set_units.

st_area returns the area of a geometry, in the coordinate reference system used; in case `x` is in degrees longitude/latitude, st_geod_area is used for area calculation.

st_length returns the length of a `LINESTRING` or `MULTILINESTRING` geometry, using the coordinate reference system. `POINT`, `MULTIPOINT`, `POLYGON` or `MULTIPOLYGON` geometries return zero.

If `by_element` is `FALSE` `st_distance` returns a dense numeric matrix of dimension length(x) by length(y); otherwise it returns a numeric vector of length `x` or `y`, the shorter one being recycled. Distances involving empty geometries are `NA`.

st_dimension, st_cast to convert geometry types

### Examples

```b0 = st_polygon(list(rbind(c(-1,-1), c(1,-1), c(1,1), c(-1,1), c(-1,-1))))
b1 = b0 + 2
b2 = b0 + c(-0.2, 2)
x = st_sfc(b0, b1, b2)
st_area(x)
line = st_sfc(st_linestring(rbind(c(30,30), c(40,40))), crs = 4326)
st_length(line)

outer = matrix(c(0,0,10,0,10,10,0,10,0,0),ncol=2, byrow=TRUE)
hole1 = matrix(c(1,1,1,2,2,2,2,1,1,1),ncol=2, byrow=TRUE)
hole2 = matrix(c(5,5,5,6,6,6,6,5,5,5),ncol=2, byrow=TRUE)

poly = st_polygon(list(outer, hole1, hole2))
mpoly = st_multipolygon(list(
list(outer, hole1, hole2),
list(outer + 12, hole1 + 12)
))

st_length(st_sfc(poly, mpoly))
p = st_sfc(st_point(c(0,0)), st_point(c(0,1)), st_point(c(0,2)))
st_distance(p, p)
st_distance(p, p, by_element = TRUE)
```

sf documentation built on July 14, 2022, 5:08 p.m.