polygrid: Coordinates of Points Inside a Polygon

Description

This function builds a rectangular grid and extracts points which are inside of an internal polygonal region.

Usage

polygrid(xgrid, ygrid, borders, vec.inout = FALSE, ...)

Value

A list with components:

xypoly: an \(n \times 2\) matrix with the coordinates of the points inside the polygon.
vec.inout: logical, a vector indicating whether each point of the rectangular grid is inside the polygon. Only returned if vec.inout = TRUE.

Arguments

xgrid: grid values in the x-direction.
ygrid: grid values in the y-direction.
borders: a matrix with polygon coordinates defining the borders of the region.
vec.inout: logical. If TRUE a logical vector is included in the output indicating whether each point of the grid is inside the polygon. Defaults to FALSE.
...: currently not used (kept for back compatibility).

Author

Paulo Justiniano Ribeiro Jr. paulojus@leg.ufpr.br,
Peter J. Diggle p.diggle@lancaster.ac.uk.

Details

The function works as follows: First it creates a grid using the R function expand.grid and then it uses the geoR' internal function .geoR_inout() which wraps usage of SpatialPoints and over from the package sp to extract the points of the grid which are inside the polygon.

Within the package geoR this function is typically used to select points in a non-rectangular region to perform spatial prediction using krige.bayes, krige.conv or ksline. It is also useful to produce image or perspective plots of the prediction results.

References

Further information on the package geoR can be found at:
http://www.leg.ufpr.br/geoR/.

Examples

Run this code

 poly <- matrix(c(.2, .8, .7, .1, .2, .1, .2, .7, .7, .1), ncol=2)
 plot(0:1, 0:1, type="n")
 lines(poly)
 poly.in <- polygrid(seq(0,1,l=11), seq(0,1,l=11), poly, vec=TRUE)
 points(poly.in$xy)

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