# R code to plot latitudinal profiles of mean elevation, along with both

# RMSE and correlation coefficients comparing fused layers with both the

# raw ASTER and with the Canada DEM

#

# Jim Regetz

# NCEAS

# Created on 08-Jun-2011

library(raster)

datadir <- "/home/regetz/media/temp/terrain/dem"

# load elevation rasters

d.aster <- raster(file.path(datadir, "aster_300straddle.tif"))

d.srtm <- raster(file.path(datadir, "srtm_150below.tif"))

d.uncor <- raster(file.path(datadir, "fused_300straddle.tif"))

d.can <- raster(file.path(datadir, "cdem_300straddle.tif"))

# extract raster latitudes for later

lats300 <- yFromRow(d.aster, 1:nrow(d.aster))

lats150 <- yFromRow(d.srtm, 1:nrow(d.srtm))

# initialize output pdf device driver

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

#

# plot latitudinal profiles of mean elevation

#

par(mfrow=c(2,2), omi=c(1,1,1,1))

lines(lats300, rowMeans(as.matrix(d.aster), na.rm=TRUE), col="blue")

lines(lats150, rowMeans(as.matrix(d.srtm), na.rm=TRUE), col="red")

legend("bottomright", legend=c("SRTM", "CDED", "ASTER"), col=c("red",

    "black", "blue"), lty=c(1, 1), bty="n")

mtext(expression(paste("Latitudinal profiles of mean elevation (",

    136*degree, "W to ", 96*degree, "W)")), adj=0, line=2, font=2)

plot(lats300, rowMeans(as.matrix(d.bg), na.rm=TRUE), type="l",

    xlab="Latitude", ylab="Mean elevation", ylim=ylim)

text(min(lats300), min(ylim)+0.5, pos=4, font=3, labels="gaussian blend")

abline(v=60, col="red", lty=2)

#

# plot latitudinal profiles of RMSE

#

# simple helper function to calculate row-wise RMSEs

rmse <- function(r1, r2, na.rm=TRUE, use) {

    diffs <- abs(as.matrix(r1) - as.matrix(r2))

    if (!missing(use)) diffs[!use] <- NA

    sqrt(rowMeans(diffs^2, na.rm=na.rm))

}

par(mfrow=c(2,3), omi=c(1,1,1,1))

ylim <- c(0, 35)

# ...with respect to ASTER

plot(lats300, rmse(d.uncor, d.aster), type="l", xlab="Latitude",

    ylab="RMSE", ylim=ylim)

lines(lats150, rmse(crop(d.uncor, extent(d.srtm)), d.srtm), col="blue")

legend("topright", legend=c("ASTER", "SRTM"), col=c("black", "blue"),

    lty=c(1, 1), bty="n")

mtext(expression(paste(

    "Elevation discrepancies with respect to separate ASTER/SRTM components (",

    136*degree, "W to ", 96*degree, "W)")), adj=0, line=2, font=2)

    lty=c(1, 1), bty="n")

plot(lats300, rmse(d.bg, d.aster), type="l", xlab="Latitude",

    ylab="RMSE", ylim=ylim)

lines(lats150, rmse(crop(d.bg, extent(d.srtm)), d.srtm), col="blue")

legend("topright", legend=c("ASTER", "SRTM"), col=c("black", "blue"),

    lty=c(1, 1), bty="n")

text(min(lats300), max(ylim)-1, pos=4, font=3, labels="gaussian blend")

abline(v=60, col="red", lty=2)

# ...with respect to CDEM

plot(lats300, rmse(d.uncor, d.can), type="l", xlab="Latitude",

    ylab="RMSE", ylim=ylim)

mtext(expression(paste(

    "Elevation discrepancies with respect to Canada DEM (",

    136*degree, "W to ", 96*degree, "W)")), adj=0, line=2, font=2)

plot(lats300, rmse(d.bg, d.can), type="l", xlab="Latitude",

    ylab="RMSE", ylim=ylim)

text(min(lats300), max(ylim)-1, pos=4, font=3, labels="gaussian blend")

abline(v=60, col="red", lty=2)

#

# plot latitudinal profiles of correlation coefficients

#

# simple helper function to calculate row-wise correlation coefficients

corByLat <- function(r1, r2, rows) {

    if (missing(rows)) {

        rows <- 1:nrow(r1)

    }

    m1 <- as.matrix(r1)

    m2 <- as.matrix(r2)

    sapply(rows, function(row) cor(m1[row,], m2[row,],

        use="pairwise.complete.obs"))

}

par(mfrow=c(2,3), omi=c(1,1,1,1))

ylim <- c(0.99, 1)

# ...with respect to ASTER

plot(lats300, corByLat(d.uncor, d.aster), type="l", xlab="Latitude",

    ylab="Correlation", ylim=ylim)

lines(lats150, corByLat(crop(d.uncor, extent(d.srtm)), d.srtm), col="blue")

legend("bottomright", legend=c("ASTER", "SRTM"), col=c("black", "blue"),

    lty=c(1, 1), bty="n")

mtext(expression(paste(

    "Elevation correlations with respect to separate ASTER/SRTM components (",

    136*degree, "W to ", 96*degree, "W)")), adj=0, line=2, font=2)

    lty=c(1, 1), bty="n")

plot(lats300, corByLat(d.bg, d.aster), type="l", xlab="Latitude",

    ylab="Correlation", ylim=ylim)

lines(lats150, corByLat(crop(d.bg, extent(d.srtm)), d.srtm), col="blue")

legend("bottomright", legend=c("ASTER", "SRTM"), col=c("black", "blue"),

    lty=c(1, 1), bty="n")

text(min(lats300), min(ylim), pos=4, font=3, labels="gaussian blend")

abline(v=60, col="red", lty=2)

# ...with respect to CDEM

plot(lats300, corByLat(d.uncor, d.can), type="l", xlab="Latitude",

    ylab="Correlation", ylim=ylim)

mtext(expression(paste(

    "Elevation correlations with respect to Canada DEM (",

    136*degree, "W to ", 96*degree, "W)")), adj=0, line=2, font=2)

plot(lats300, corByLat(d.bg, d.can), type="l", xlab="Latitude",

    ylab="Correlation", ylim=ylim)

text(min(lats300), min(ylim), pos=4, font=3, labels="gaussian blend")

abline(v=60, col="red", lty=2)

# close pdf device driver

dev.off()