# colormap

April 30, 2014
By

(This article was first published on Dan Kelley Blog/R, and kindly contributed to R-bloggers)

# Introduction

Over the past month or so I have been trying different ways of handling GMT-style colormaps in Oce. I think my present solution is on the right track, but I am posting here to get more eyes on the problem.

Note that the function called `Colormap()` here will be called `colormap()` if I decided to incorporate it into Oce. That will mean that it replaces an old function of the same name. Also, as part of the change, the old function `colorize()` will disappear. (To call them “old” is a stretch. They are about a month old and were marked as “Alpha” code from the start.)

# Procedure

The following code is direct from the help for `Colormap()`; all I’ve done is to put the example code into Rmarkdown to make for easier comparision with the resultant graphs.

 ``1`` ```library(oce) ```
``````## Loading required package: methods
``````
 `````` 1 2 3 4 5 6 7 8 9 10`````` ```## Example 1. color scheme for points on xy plot x <- seq(0, 1, length.out = 40) y <- sin(2 * pi * x) par(mar = c(3, 3, 1, 1)) mar <- par("mar") # prevent margin creep by drawPalette() ## First, default breaks c <- Colormap(y) drawPalette(c\$zlim, col = c\$col, breaks = c\$breaks) plot(x, y, bg = c\$zcol, pch = 21, cex = 1) grid() ```

 ``````1 2 3 4 5 6`````` ```par(mar = mar) ## Second, 100 breaks, yielding a smoother palette c <- Colormap(y, breaks = 100) drawPalette(c\$zlim, col = c\$col, breaks = c\$breaks) plot(x, y, bg = c\$zcol, pch = 21, cex = 1) grid() ```

 ``````1 2 3 4 5 6 7`````` ```par(mar = mar) ## Example 2. topographic image with a standard color scheme par(mfrow = c(1, 1)) data(topoWorld) cm <- Colormap(name = "gmt_globe") imagep(topoWorld, breaks = cm\$breaks, col = cm\$col) ```

 ``````1 2 3 4 5 6 7`````` ```## Example 3. topographic image with modified colors cm <- Colormap(name = "gmt_globe") deep <- cm\$x0 < -4000 cm\$col0[deep] <- "black" cm\$col1[deep] <- "black" cm <- Colormap(x0 = cm\$x0, x1 = cm\$x1, col0 = cm\$col0, col1 = cm\$col1) imagep(topoWorld, breaks = cm\$breaks, col = cm\$col) ```

 `````` 1 2 3 4 5 6 7 8 9 10 11`````` ```## Example 4. image of world topography with water colorized smoothly from ## violet at 8km depth to blue at 4km depth, then blending in 0.5km ## increments to white at the coast, with tan for land. cm <- Colormap(x0 = c(-8000, -4000, 0, 100), x1 = c(-8000, -4000, 0, 100), col0 = c("violet", "blue", "white", "tan"), col1 = c("violet", "blue", "white", "tan"), n = c(100, 8, 1)) lon <- topoWorld[["longitude"]] lat <- topoWorld[["latitude"]] z <- topoWorld[["z"]] imagep(lon, lat, z, breaks = cm\$breaks, col = cm\$col) contour(lon, lat, z, levels = 0, add = TRUE) ```

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