sf (version 0.2-8)

st_graticule: compute graticules and their parameters

Description

compute graticules and their parameters

Usage

st_graticule(x = c(-180, -90, 180, 90), crs = st_crs(x), datum = st_crs(4326), ..., lon = pretty(st_bbox(box)[c(1, 3)]), lat = pretty(st_bbox(box)[c(2, 4)]), ndiscr = 100)

Arguments

x

object of class sf, sfc or sfg or numeric vector with bounding box (minx,miny,maxx,maxy).

crs

object of class crs, with the display coordinate reference system

datum

object of class crs, with the coordinate reference system for the graticules

...

ignored

lon

numeric; degrees east for the meridians

lat

numeric; degrees north for the parallels

ndiscr

integer; number of points to discretize a parallel or meridian

Value

an object of class sf with additional attributes describing the type (E: meridian, N: parallel) degree value, label, start and end coordinates and angle; see example.

Examples

library(sp)
library(maps)

m = map('usa', plot = FALSE, fill = TRUE)
ID0 <- sapply(strsplit(m$names, ":"), function(x) x[1])

library(maptools)
m <- map2SpatialPolygons(m, IDs=ID0, proj4string = CRS("+init=epsg:4326"))

library(sf)

laea = st_crs("+proj=laea +lat_0=30 +lon_0=-95") # Lambert equal area
m <- st_transform(st_as_sf(m), laea)

bb = st_bbox(m)
bbox = st_linestring(rbind(c( bb[1],bb[2]),c( bb[3],bb[2]),
   c( bb[3],bb[4]),c( bb[1],bb[4]),c( bb[1],bb[2])))

g = st_graticule(m)
plot(m, xlim = 1.2 * c(-2450853.4, 2186391.9))
plot(g[1], add = TRUE, col = 'grey')
plot(bbox, add = TRUE)
points(g$x_start, g$y_start, col = 'red')
points(g$x_end, g$y_end, col = 'blue')

invisible(lapply(seq_len(nrow(g)), function(i) {
if (g$type[i] == "N" && g$x_start[i] - min(g$x_start) < 1000)
	text(g[i,"x_start"], g[i,"y_start"], labels = parse(text = g[i,"degree_label"]), 
		srt = g$angle_start[i], pos = 2, cex = .7)
if (g$type[i] == "E" && g$y_start[i] - min(g$y_start) < 1000)
	text(g[i,"x_start"], g[i,"y_start"], labels = parse(text = g[i,"degree_label"]), 
		srt = g$angle_start[i] - 90, pos = 1, cex = .7)
if (g$type[i] == "N" && g$x_end[i] - max(g$x_end) > -1000)
	text(g[i,"x_end"], g[i,"y_end"], labels = parse(text = g[i,"degree_label"]), 
		srt = g$angle_end[i], pos = 4, cex = .7)
if (g$type[i] == "E" && g$y_end[i] - max(g$y_end) > -1000)
	text(g[i,"x_end"], g[i,"y_end"], labels = parse(text = g[i,"degree_label"]), 
		srt = g$angle_end[i] - 90, pos = 3, cex = .7)
}))
plot(m, graticule = st_crs(4326), axes = TRUE, lon = seq(-60,-130,by=-10))