R/slopeasp.R

In landsat: Radiometric and Topographic Correction of Satellite Imagery

slopeasp <- function (x, EWres, NSres, EWkernel, NSkernel, smoothing = 1) 
{
    if(is(x, "SpatialGridDataFrame")) {
    	xmat <- t(as.matrix(x))
    }
    else {
       xmat <- as.matrix(x)
    }
    if (missing(EWres)) {
        if (is(x, "SpatialGridDataFrame")) {
            EWres <- slot(getGridTopology(x), "cellsize")[1]
        }
        else {
            stop("EWres must be specified if x is not a SpatialGridDataFrame.\n")
        }
    }
    if (missing(NSres)) {
        if (is(x, "SpatialGridDataFrame")) {
            NSres <- slot(getGridTopology(x), "cellsize")[2]
        }
        else {
            stop("NSres must be specified if x is not a SpatialGridDataFrame.\n")
        }
    }
    if (missing(EWkernel)) {
        EWkernel <- matrix(c(-1/8, 0, 1/8, -2/8, 0, 2/8, -1/8, 
            0, 1/8), ncol = 3, nrow = 3, byrow = TRUE)
    }
    EW.mat <- movingwindow(xmat, EWkernel)/EWres
    if (missing(NSkernel)) {
        NSkernel <- matrix(c(1/8, 2/8, 1/8, 0, 0, 0, -1/8, -2/8, 
            -1/8), ncol = 3, nrow = 3, byrow = TRUE)
    }
    NS.mat <- movingwindow(xmat, NSkernel)/NSres

    slope <- atan(sqrt(EW.mat^2 + NS.mat^2)/smoothing)
    slope <- (180/pi) * slope

    aspect <- 180 - (180/pi) * atan(NS.mat/EW.mat) + 90 * (EW.mat/abs(EW.mat))

    aspect[slope == 0] <- 0

    if (is(x, "SpatialGridDataFrame")) {
        temp <- x
        temp@data[, 1] <- as.vector(t(aspect))
        aspect <- temp
        temp@data[, 1] <- as.vector(t(slope))
        slope <- temp
    }
    list(slope = slope, aspect = aspect)
}