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. Strickly speaking, being 'on land' is in fact being inside a polygon of the shapefile.

Usage

findLand(x, ...)

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

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

# S4 method for 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 SpatialPolygonsDataFrame (see readShapePoly in maptools package to import such data from a GIS shapefile). Alternatively, a character string indicating one shapefile released with geoGraph; currently, only 'world' is available (see ?data(worldshape)).

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

extractFromLayer, 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  64.90256 -40.73078
#> 2  13.32480 -62.62872
#> 3 -58.33955  68.65494
#> ...
#> 
#> @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)

## find which points are on land
obj <- findLand(obj)
obj # note: new node attribute
#> 
#> === gGraph object ===
#> 
#> @coords: spatial coordinates of 1000 nodes
#>         lon       lat
#> 1  64.90256 -40.73078
#> 2  13.32480 -62.62872
#> 3 -58.33955  68.65494
#> ...
#> 
#> @nodes.attr: 1 nodes attributes
#>   habitat
#> 1     sea
#> 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$color <- temp

## plot object with new colors
plot(obj)