Extract environmental data to presence locations

Description

Given a matrix of quadrature points and a list of species presences, this function extracts environmental data to presence locations using bilinear interpolation.

Usage

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env.var(sp.xy, env.grid, env.scale, coord = c("X", "Y"), file.name = NA)

Arguments

sp.xy

A matrix of species locations containing at least one column representing longitude and one column representing latitude.

env.grid

The geo-referenced matrix of environmental grids.

env.scale

The spatial resolution of the quadrature scheme from which the environmental data is extracted.

coord

A vector containing the names of the longitude and latitude coordinates, as in sample.quad.

file.name

An optional argument containing the name of the saved file. Setting file.name = "Sp Env" will save a matrix sp.dat containing the species presence locations and the interpolated environmental data to the file "Sp Env.RData".

Details

At a given species location with coordinates (x, y), the interpolated value of the environmental variable z is calculated as a weighted average of z at four reference quadrature points (x^{(1)}, y^{(1)}), (x^{(1)}, y^{(2)}), (x^{(2)}, y^{(1)}) and (x^{(2)}, y^{(2)}) that form a square of nominated side length env.scale surrounding (x, y).

Value

A matrix containing locations of species presences in the first two columns and the interpolated environmental data in the remaining columns.

Author(s)

Ian W. Renner

Examples

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data(BlueMountains)
species.env = env.var(BlueMountains$eucalypt, env.grid = BlueMountains$env, env.scale = 0.5,
file.name = "Sp Env Data")