customAlbers {enmSdmX}

Custom coordinate reference system WKT2 string

Description

These functions take as input either a spatial object or coordinate pair and a custom WKT2 (well-known text) coordinate reference system string centered on the object or coordinate. Projections include:

• Albers conic equal-area

• Lambert azimuthal equal-area

• Vertical near-side (i.e., as the world appears from geosynchronous orbit)

Please note that these are NOT standard projections, so do not have an EPSG or like code.

Usage

customAlbers(x)

customLambert(x)

customVNS(x, alt = 35800)

Arguments

x

Either an object of class SpatRaster, SpatVector, or sf, or a numeric vector with two values (longitude and latitude of the center of the projection), or a two-column matrix/data frame with the centroid of the projection.

alt

Altitude in meters of the viewpoint in km. The default (35800 km) is geosynchronous orbit.

Value

A WKT2 (well-known text) string.

Functions

• customLambert(): Custom coordinate reference system WKT2 string

• customVNS(): Custom coordinate reference system WKT2 string

See Also

getCRS, customAlbers, customLambert, customVNS

Examples

library(sf)

# Madagascar
data(mad0)

alb <- customAlbers(mad0)
lamb <- customLambert(mad0)
vert <- customVNS(mad0)

madAlb <- st_transform(mad0, alb)
madLamb <- st_transform(mad0, lamb)
madVert <- st_transform(mad0, vert)

oldPar <- par(mfrow=c(2, 2))

plot(st_geometry(mad0), main='Unprojected (WGS84)')
plot(st_geometry(madAlb), main='Albers')
plot(st_geometry(madLamb), main='Lambert')
plot(st_geometry(madVert), main='Vertical')

par(oldPar)


# The effect is more noticeable when plotting large areas,
# especially if they lie near the poles.
# This example can take a few minutes to run and plot.

library(geodata)
library(terra)

# Get outline of Canada...
# We wrap this in tryCatch() in case the server is down.
can <- tryCatch(
	gadm('CAN', level=0, path=tempdir(), resolution=2),
	error=function(cond) FALSE
)

if (!is.logical(can)) {

	alb <- customAlbers(can)
	lamb <- customLambert(can)
	vert <- customVNS(can)

	canAlb <- project(can, alb)
	canLamb <- project(can, lamb)
	canVert <- project(can, vert)

	oldPar <- par(mfrow=c(2, 2))

	plot(can, main='Unprojected (WGS84)')
	plot(canAlb, main='Albers')
	plot(canLamb, main='Lambert')
	plot(canVert, main='Vertical')
		
	par(oldPar)
	
}