ppmlasso (version 1.4)

griddify: Ensure that a geo-referenced matrix of environmental grids is rectangular

Description

This function ensures that the coordinates of the supplied geo-referenced matrix of environmental grids constitutes a rectangular grid.

Usage

griddify(envframe, tol = 0.01, coord = c("X", "Y"))

Value

A data frame containing the coordinates on a rectangular grid as well as any environmental variables left unchanged.

Arguments

envframe

The geo-referenced matrix of environmental grids.

tol

The tolerance level within which to correct coordinate errors.

coord

A vector containing the names of the longitude and latitude coordinates.

Author

Ian W. Renner

Details

The functions in the ppmlasso package require a set of quadrature points along a rectangular grid. At times a set of quadrature points with a desired spatial resolution of \(x_\delta \times y_\delta\) will have some minor machine error in some coordinates such that the coordinates as supplied do not consistute a rectangular grid. The griddify function corrects this error as follows:

Let \(\{x_1, x_2, \ldots, x_n\}\) and \(\{y_1, y_2, \ldots, y_n\}\) be the supplied coordinates contained in envframe. The function first determines the spatial resolution \(x_\delta \times y_\delta\) based on the median of the differences in the unique values of \(x_i\) and \(y_i\) as well as the coordinates of a rectangular grid with this spatial resolution \(\{x^{grid}_1, x^{grid}_2, \ldots, x^{grid}_n\}\) and \(\{y^{grid}_1, y^{grid}_2, \ldots, y^{grid}_n\}\). Given the tolerance \(\epsilon\) supplied to tol, any coordinate \(x_i\) for which \(0 < \left|x_i - x^{grid}_i\right| \leq \epsilon \times x_\delta\) will be adjusted to \(x^{grid}_i\). Likewise, any coordinate \(y_i\) for which \(0 < \left|y_i - y^{grid}_i\right| \leq \epsilon \times y_\delta\) will be adjusted to \(y^{grid}_i\).

Any environmental variables contained in envframe are left unchanged.

Examples

X = seq(0, 5, 1)
Y = seq(1, 11, 2)
XY = expand.grid(X, Y) # generate 1 x 2 rectangular grid
names(XY) = c("X", "Y")
#move some coordinates off of rectangular grid
XY$X[1] = XY$X[1] - 0.01
XY$Y[1] = XY$Y[1] - 0.01
XY$X[7] = XY$X[7] + 0.01
XY$Y[7] = XY$Y[7] + 0.01

#generate environmental variables
XY$V1 = 0.1*XY$X + 0.2*XY$Y + rnorm(36, 0, 1)
XY$V2 = -0.2*XY$X + 0.1*XY$Y + 0.05*XY$X*XY$Y + rnorm(36, 0, 5)

XY_grid = griddify(XY)