Find which nodes are on land

The generic function findLand uses information from a GIS shapefile to define which nodes are on land, and which are not. Strictly speaking, being 'on land' is in fact being inside a polygon of the shapefile.

Usage

findLand(x, ...)

# S4 method for class 'matrix'
findLand(x, shape = "world", ...)

# S4 method for class 'data.frame'
findLand(x, shape = "world", ...)

# S4 method for class 'gGraph'
findLand(x, shape = "world", attr.name = "habitat", ...)

Arguments

x

a matrix, a data.frame, or a valid gGraph object. For matrix and data.frame, input must have two columns giving longitudes and latitudes of locations being considered.

...

further arguments to be passed to other methods. Currently not used.

shape

a shapefile of the class sf (see sf::st_read() to import a GIS shapefile). Alternatively, a character string indicating one shapefile released with geoGraph; currently, only 'world' is available.

attr.name

a character string giving the name of the node attribute in which the output is to be stored.

Value

The output depends on the nature of the input:
- matrix, data.frame: a factor with two levels being 'land' and 'sea'.

• gGraph: a gGraph object with a new node attribute, possibly added to previously existing node attributes (@nodes.attr slot).
  

Details

Nodes can be specified either as a matrix of geographic coordinates, or as a gGraph object.

See also

assignByPolygon, to retrieve any information from a GIS shapefile.

Examples

## create a new gGraph with random coordinates
myCoords <- data.frame(long = runif(1000, -180, 180), lat = runif(1000, -90, 90))
obj <- new("gGraph", coords = myCoords)
obj # note: no node attribute
#> 
#> === gGraph object ===
#> 
#> @coords: spatial coordinates of 1000 nodes
#>         lon       lat
#> 1 151.86631 -72.25429
#> 2  48.34813  76.86184
#> 3 -71.79669 -20.55676
#> ...
#> 
#> @nodes.attr: 0 nodes attributes
#> data frame with 0 columns and 0 rows
#> 
#> @meta: list of meta information with 0 items
#> 
#> @graph:
#> A graphNEL graph with undirected edges
#> Number of Nodes = 1000 
#> Number of Edges = 0 
plot(obj)
#> Spherical geometry (s2) switched off

#> Spherical geometry (s2) switched on

## find which points are on land
obj <- findLand(obj)
#> Spherical geometry (s2) switched off
#> although coordinates are longitude/latitude, st_intersects assumes that they
#> are planar
#> Spherical geometry (s2) switched on
obj # note: new node attribute
#> 
#> === gGraph object ===
#> 
#> @coords: spatial coordinates of 1000 nodes
#>         lon       lat
#> 1 151.86631 -72.25429
#> 2  48.34813  76.86184
#> 3 -71.79669 -20.55676
#> ...
#> 
#> @nodes.attr: 1 nodes attributes
#>   habitat
#> 1    land
#> 2     sea
#> 3     sea
#> ...
#> 
#> @meta: list of meta information with 0 items
#> 
#> @graph:
#> A graphNEL graph with undirected edges
#> Number of Nodes = 1000 
#> Number of Edges = 0 

## define rules for colors
temp <- data.frame(habitat = c("land", "sea"), color = c("green", "blue"))
temp
#>   habitat color
#> 1    land green
#> 2     sea  blue
obj@meta$colors <- temp

## plot object with new colors
plot(obj)
#> Spherical geometry (s2) switched off

#> Spherical geometry (s2) switched on