# initialize output pdf device driver

pdf("elevation-assessment.pdf", height=8, width=11.5)

#

# plot pattern of ASTER-SRTM deltas as a function of ASTER elevation

#

plotMeanDeltaByElev <- function(delta.vals, elev, ...) {

    mean.by.elev <- tapply(delta.vals, elev, mean)

    sd.by.elev <- tapply(delta.vals, elev, sd)

    n.by.elev <- tapply(delta.vals, elev, length)

    se.by.elev <- sd.by.elev/sqrt(n.by.elev)

    na.se.points <- mean.by.elev[is.na(se.by.elev)]

    se.by.elev[is.na(se.by.elev)] <- 0

    elev <- as.numeric(names(mean.by.elev))

    plot(elev, mean.by.elev, pch=16,

        xlim=c(0, max(elev)), ylim=c(min(mean.by.elev -

        se.by.elev), max(mean.by.elev + se.by.elev)), type="n", ...)

    segments(elev, mean.by.elev-se.by.elev,

        as.numeric(names(mean.by.elev)), mean.by.elev+se.by.elev,

        col="grey")

    points(elev, mean.by.elev, pch=".")

    points(as.numeric(names(na.se.points)), na.se.points, pch=4,

        col="red", cex=0.5)

}

d.aster.crop.vals <- values(crop(d.aster, extent(d.srtm)))

d.srtm.vals <- values(d.srtm)

delta.vals <- d.aster.crop.vals - d.srtm.vals

plotMeanDeltaByElev(delta.vals, d.aster.crop.vals,

    xlab="ASTER elevation (m)", ylab="ASTER-SRTM difference (m)")

plotDeltaBins <- function(delta.vals, elev, bin.min, bin.width, bin.max=1500,

    outline=FALSE, ...) {

    breaks <- seq(bin.min, bin.max, by=bin.width)

    midpts <- c(

        paste("<", bin.min, sep=""),

        head(breaks, -1) + bin.width/2,

        paste(">", bin.max, sep=""))

    elev <- cut(elev, breaks=c(0, breaks, Inf), labels=midpts)

    bp <- boxplot(delta.vals ~ elev, outline=outline, col="lightgray",

        frame=FALSE, ...)

    text(1:length(bp$n), bp$stats[5,], labels=round(bp$n/1000),

        pos=3, cex=0.5, offset=0.2, font=3, col="gray")

    #axis(3, at=seq_along(bp$n), labels=paste(round(bp$n/1000), "k", sep=""),

    #    cex.axis=0.7, tick=FALSE, font=3, line=-1)

    #mtext("n =", side=3, adj=0, font=3, cex=0.7)

    abline(h=median(delta.vals), col="red", lty=2)

    invisible(bp)

}

d.aster.crop.vals <- values(crop(d.aster, extent(d.srtm)))

d.srtm.vals <- values(d.srtm)

delta.vals <- d.aster.crop.vals - d.srtm.vals

#  d.aster.crop.vals <- d.aster.crop.vals[d.srtm.vals>0]

#  d.srtm.vals <- d.srtm.vals[d.srtm.vals>0]

png("aster-srtm-bins.png", height=5, width=8, units="in", res=300)

plotDeltaBins(delta.vals, d.aster.crop.vals, 150, 50, 1500, las=2,

    cex.axis=0.8, xlab="Midpoints of ASTER elevation bins (m)",

    ylab="(ASTER - SRTM)")

dev.off()

# plot scatter of aster vs srtm

png("aster-srtm-scatter.png", height=5, width=8, units="in", res=300)

plot(jitter(d.srtm.vals), jitter(d.aster.crop.vals), pch=".",

    xlab="SRTM elevation (m)", ylab="ASTER elevation (m)", cex=0.5)

abline(median(delta.vals), 1, col="red", cex=0.5)

abline(0, 1, col="blue", lty=2, cex=0.5)

dev.off()