Pole centric map with Raster?

On 03/27/2015 10:14 PM, Tim Appelhans wrote:

Ben
here's some code I used for a paper.

Is this producing what you want?

Cool!

The ggplot2 example of Ben looks as if it plots cells that form a
rectangular grid in long-lat onto a polar stereographic projection. One
could do this by converting the raster to a SpatialPolygonsDataFrame,
rgdal::spTransform this to the new projection, and then plot. It might
be improved by not plotting the cell (polygon) boundaries.

library("remote")

###### EXAMPLE I ##########################################################
###########################################################################
library("rworldmap")
library("rgdal")
library("rgeos")
library("gridExtra")
library("RColorBrewer")

## load data
data("vdendool")
data("coastsCoarse")

## calculate 4 leading modes
nh_modes <- eot(x = vdendool, y = NULL, n = 4, reduce.both = FALSE,
               standardised = FALSE, verbose = TRUE)

## create coastal outlines
ster <- CRS("+proj=stere +lat_0=90 +lon_0=-45")
xmin <- -180
xmax <- 180
ymin <- 20
ymax <- 90     # Coordinates for bounding box
bb <- cbind(x = c(xmin, xmin, xmax, xmax, xmin),
           y = c(ymin, ymax, ymax, ymin, ymin))    #Create bounding box
SP <- SpatialPolygons(list(Polygons(list(Polygon(bb)), "1")),
                     proj4string = CRS(proj4string(coastsCoarse)))

gI <- gIntersects(coastsCoarse, SP, byid = TRUE)
out <- vector(mode = "list", length = length(which(gI)))
ii <- 1

for (i in seq(along = gI)) if (gI[i]) {
 out[[ii]] <- gIntersection(coastsCoarse[i, ], SP)
 row.names(out[[ii]]) <- row.names(coastsCoarse)[i]
 ii <- ii + 1
}

nh_coasts <- do.call("rbind", out)
nh_coasts_ster <- spTransform(nh_coasts, ster)

lout <- list("sp.lines", nh_coasts_ster,
            col = "grey30", grid = TRUE)

## define colours
clrs <- colorRampPalette(rev(brewer.pal(9, "RdBu")))

## project modes to polar stereographic CRS
mode1 <- projectRaster(nh_modes[[1]]@r_predictor, crs = ster)

spplot(mode1, sp.layout = lout,
      col.regions = clrs(1000), at = seq(-1, 1, 0.2),
      par.settings = list(axis.line = list(col = 0)),
      colorkey = list(height = 0.75, width = 1))


Tim



On 27.03.2015 21:20, Ben Tupper wrote:

Hello,

I'm learning how to use Raster* objects and ultimately hope to draw
rasters from a (north) polar perspective.  I can do something like
this using tiling in ggplot2:

https://dl.dropboxusercontent.com/u/8433654/polar-map-with-matrix.png


I have hopes of doing similar using raster, sp and lattice.  But I'm
drowning in information as neophytes are prone to do.  Below is a
self-contained example...  I'm not getting too far.  It creates two
plots:

raster without using projectRaster:
https://dl.dropboxusercontent.com/u/8433654/raster_no_project.png

raster using projectRaster:
https://dl.dropboxusercontent.com/u/8433654/raster_with_project.png

Neither is what I would like.  How does one get the map centered on
the pole and draw a (warped) raster using spplot?

Thanks!
Ben


##### START
library(raster)
library(maps)
library(maptools)
library(rgdal)

# create a Raster from 'volcano'
my_proj <- "+proj=stere +lat_0=90 +lon_0=-30 +x_0=0 +y_0=0"
r <- raster(volcano,
   xmn = -90, xmx = 0, ymn = 50, ymx = 85,
   crs = my_proj)
# class       : RasterLayer
# dimensions  : 87, 61, 5307  (nrow, ncol, ncell)
# resolution  : 1.47541, 0.4022989  (x, y)
# extent      : -90, 0, 50, 85  (xmin, xmax, ymin, ymax)
# coord. ref. : +proj=stere +lat_0=90 +lon_0=-30 +x_0=0 +y_0=0
+ellps=WGS84
# data source : in memory
# names       : layer
# values      : 94, 195  (min, max)

pr <- projectRaster(r, crs=my_proj)
# class       : RasterLayer
# dimensions  : 123, 71, 8733  (nrow, ncol, ncell)
# resolution  : 1.48, 0.402  (x, y)
# extent      : -97.4, 7.68, 42.79, 92.236  (xmin, xmax, ymin, ymax)
# coord. ref. : +proj=stere +lat_0=90 +lon_0=-30 +x_0=0 +y_0=0
+ellps=WGS84
# data source : in memory
# names       : layer
# values      : 93.88372, 194.8761  (min, max)

# create a coastline and transform to the projection
mp <- map2SpatialLines(map(plot = FALSE, interior = FALSE),
proj4string = CRS(my_proj))
mp <- spTransform(mp, CRSobj = CRS(my_proj))
# class       : SpatialLines
# features    : 2904
# extent      : -179.9572, 190.2908, -85.44308, 83.57391  (xmin, xmax,
ymin, ymax)
# coord. ref. : +proj=stere +lat_0=90 +lon_0=-30 +x_0=0 +y_0=0
+ellps=WGS84

# show the map with the 'unprojected' raster
plot_r <- spplot(r,
   sp.layout = list( sp.lines, mp, first = FALSE)
)

# show the map with the projected raster
plot_pr <- spplot(pr,
   sp.layout = list( sp.lines, mp, first = FALSE)
)

print(plot_r)
print(plot_pr)
##### END

sessionInfo()

R version 3.1.2 (2014-10-31)
Platform: x86_64-apple-darwin13.4.0 (64-bit)

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] rgdal_0.9-2     maptools_0.8-34 maps_2.3-9      raster_2.3-33  
sp_1.0-17

loaded via a namespace (and not attached):
[1] foreign_0.8-63  grid_3.1.2      lattice_0.20-30 tools_3.1.2


Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi),  University of M?nster,
Heisenbergstra?e 2, 48149 M?nster, Germany; +49 251 83 33081
Journal of Statistical Software:   http://www.jstatsoft.org/
Computers & Geosciences:   http://elsevier.com/locate/cageo/
Spatial Statistics Society http://www.spatialstatistics.info