R/gridmat.R

In baddstats/spherstat: Spatial Point Pattern Analysis, Geometry and Trigonometry for the Sphere

gridmat <- function(colats, lons, ncolat=100, nlon=100, cellarea=FALSE) {
	stopifnot(colats[1] < colats[2] && lons[1] < lons[2])
	ctheta <- seq(from=cos(colats[1]), to=cos(colats[2]), length=ncolat+1)
	phi <- seq(from=lons[1], to=lons[2], length=nlon+1)
	thetas <- acos(ctheta[1:ncolat] + (ctheta[2:(ncolat+1)] - ctheta[1:ncolat])/2)
	phis <- phi[1:nlon]+((phi[2:(nlon+1)] - phi[1:nlon])/2)
	thetaslist <- rep(thetas, each=nlon)
	phislist <- rep(phis, times=ncolat)
	gridrefs <- cbind(thetaslist, phislist)
	if(cellarea) {
		dtheta <- diff(ctheta)
		cellarea <- rep(dtheta, each=nlon)*(phi[2]-phi[1])
		gridrefs <- cbind(gridrefs, cellarea)
	}
	gridrefs
}