Given a matrix of quadrature points and a list of species presences, this function extracts environmental data to presence locations using bilinear interpolation.
getEnvVar(sp.xy, env.grid, env.scale, coord = c("X", "Y"), envfilename = "SpEnvData",
tol = 0.01, writefile = TRUE)A matrix containing locations of species presences in the first two columns and the interpolated environmental data in the remaining columns.
A matrix of species locations containing at least one column representing longitude and one column representing latitude.
The geo-referenced matrix of environmental grids.
The spatial resolution of the quadrature scheme from which the environmental data is extracted.
A vector containing the names of the longitude and latitude coordinates,
as in sampleQuad.
An optional argument containing the name of the saved file. Setting
envfilename = "SpEnvData" will save a matrix sp.dat containing the species presence
locations and the interpolated environmental data to the file "SpEnvData.RData".
An optional argument to specify the tolerance level of coordinate error passed to an internal call to the griddify function, set to 0.01 by default.
A logical argument to determine whether the output should be written to a file or not. If TRUE (the default), the output will be saved with the file name as described in the envfilename argument.
Ian W. Renner
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 \((x, y)\).
data(BlueMountains)
species.env = getEnvVar(BlueMountains$eucalypt, env.grid = BlueMountains$env, env.scale = 0.5,
envfilename = NA, writefile = FALSE)
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