interpPolysByTween: Spatial interpolation between polygon borders using tweening

In adamlilith/birdsEye: Tools for geographic analysis

Description

This function recreates stages in the morphing of one SpatialPolygon* to another. The output is a SpatialPolygons object with borders that are "between" the borders of two other SpatialPolygons* objects. This particular function uses spatial tweening to estimate vertices of polygons.

Usage

interpPolysByTween(
  x1,
  x2,
  between,
  delta = 20,
  eaCrs = "oae",
  method = "cubic-in-out",
  verbose = TRUE
)

Arguments

x1	SpatialPolygon or SpatialPolygonDataFrame object in an unprojected (WGS84) coordinate reference system.
x2	SpatialPolygon or SpatialPolygonDataFrame object in an unprojected (WGS84) coordinate reference system.
between	Numeric between 0 and 1. This is the relative distance from x1 to x2 to place the interpolated border (higher values of delta increase precision but also increase computational time). A value of 0 should return a polygon the same as x1 and a value of 1 should return a polygon the same as x2.
delta	Positive numeric, represents distance (typically in meters) by which to grow the buffer at each step. Smaller values yield more accurate interpolation but increase processing time.
eaCrs	This is either a proj4 string, an object of class CRS, or an abbreviated name of equal-area projection to use. The polygons will be projected to this coordinate reference system before interpolation. Ideally, the center point of the projection should be in the center of the polygons to minimize distortion. See makeCRS. Options include: 'laea': Lambert azimuthal equal-area 'mollweide': Mollweide (equal-area) 'oae' (default) or aeqd: oblique azimuthal equidistant projection
method	"Ease" method used to optimize tweened polygons. Any of: 'linear', 'quadratic', 'cubic', 'quartic', 'quintic', 'sine', 'circular', 'exponential', 'elastic', 'back', 'bounce'. For example, 'cubic-in-out' or 'linear-in-out'. See display_ease.
verbose	Logical. If TRUE then display progress indicators.

Details

Although higher values of delta may seem to generate smoother translations, in some cases smaller values can address weirdnesses (e.g., holes that appear and disappear then appear again).

Value

SpatialPolygons object.

Examples

# create "x1": has two sub-polygons
x <- c(44.02, 43.5, 42.61, 42.18, 42, 42.41, 42.75, 41.75, 41.49,
43.61,46.02, 46.5, 47.5, 47.39, 48.64, 49.05, 48.46, 48.18, 47.54, 46.73, 45.80, 45.59)
y <- c(-18.83, -18.67, -18.87, -19.67, -20.65, -21.64, -23.08, -24.9,
-26.51, -27.09, -26.74, -25.6, -25.14, -26.44, -26.46, -24.96, -23.63,
 -22.72, -23.36, -22.29, -21.45, -20.69)
xy1a <- cbind(x, y)

x <- c(40.61, 40.07, 40.23, 41.38, 41.38)
y <- c(-20.51, -20.49, -21.11, -21.55, -21.01)
xy1b <- cbind(x, y)

x1a <- coordsToPoly(xy1a, enmSdm::getCRS('wgs84'))
x1b <- coordsToPoly(xy1b, enmSdm::getCRS('wgs84'))
x1 <- rgeos::gUnion(x1a, x1b)

# create "x2"
x <- c(44.53, 44.18, 44.00, 42.93, 42.29, 42.71, 43.43, 47.15, 48.08,
 45.94,45.36, 45.76, 46.97, 46.87, 45.94, 45.97, 45.08, 44.50, 44.58)
y <- c(-24.27, -23.68, -22.86, -21.88, -20.56, -19.31, -20.36, -20.53,
 -20.93,-21.81, -21.64, -22.90, -23.44, -24.08, -24.76, -25.95, -25.88, -25.61, -24.46)
xy2 <- cbind(x, y)

x2 <- coordsToPoly(xy2, enmSdm::getCRS('wgs84'))

eaCrs <- enmSdm::getCRS('albersNA')

interBuff <- interpPolysByBuffer(
	x1, x2, eaCrs=eaCrs, between = 0.4, delta=10000
)

interTween <- interpPolysByTween(
	x1, x2, eaCrs='laea', between = 0.4, delta=100
)

interTween <- interTween[[1]]$poly

plot(x1, col='gray90')
plot(x2, add=TRUE)
plot(interBuff, border='red', add=TRUE)
plot(interTween, border='green', add=TRUE)
legend('bottomleft',
	legend=c('x1', 'x2', 'by buffer', 'by tween'),
	fill=c('gray90', NA, NA, NA),
	border=c('black', 'black', 'red', 'green'),
	bty='n'
)

## multiple steps
between <- seq(0, 1, by=0.1)
interTween <- interpPolysByTween(
	x1, x2, eaCrs='laea', between = between, delta=100
)

plot(x1, col='gray90')
plot(x2, add=TRUE)
for (i in seq_along(between)) {
	plot(interTween[[i]]$poly, border='green', lty='dotted', add=TRUE)
}

legend('bottomleft',
	legend=c('x1', 'x2', 'tweens'),
	fill=c('gray90', NA, NA),
	border=c('black', 'black', 'green'),
	bty='n'
)

adamlilith/birdsEye documentation built on May 23, 2020, 4:40 p.m.