marmap (version 1.0.10)

lc.dist: Computes least cost distances between two or more locations

Description

Computes least cost distances between two or more locations

Usage

lc.dist(trans, loc, res = c("dist", "path"), meters = FALSE, round = 0)

Value

Results can be presented either as a kilometric distance matrix between all possible pairs of locations (argument res="dist") or as a list of paths (i.e. 2-columns matrices of routes) between pairs of locations (res="path").

Arguments

trans

transition object as computed by trans.mat

loc

A two-columns matrix or data.frame containing latitude and longitude for 2 or more locations.

res

either "dist" or "path". See details.

meters

logical. When res = "dist", should the results be returned in kilometers (default) or in meters.

round

integer indicating the number of decimal places to be used for printing results when res = "dist".

Author

Benoit Simon-Bouhet

Details

lc.dist computes least cost distances between 2 or more locations. This function relies on the package gdistance (van Etten, 2011. https://CRAN.R-project.org/package=gdistance) and on the trans.mat function to define a range of depths where the paths are possible.

References

Jacob van Etten (2011). gdistance: distances and routes on geographical grids. R package version 1.1-2. https://CRAN.R-project.org/package=gdistance

See Also

trans.mat

Examples

# Load and plot bathymetry
	data(hawaii)
	pal <- colorRampPalette(c("black","darkblue","blue","lightblue"))
	plot(hawaii,image=TRUE,bpal=pal(100),asp=1,col="grey40",lwd=.7,
	     main="Bathymetric map of Hawaii")

# Load and plot several locations
	data(hawaii.sites)
	sites <- hawaii.sites[-c(1,4),]
	rownames(sites) <- 1:4
	points(sites,pch=21,col="yellow",bg=col2alpha("yellow",.9),cex=1.2)
	text(sites[,1],sites[,2],lab=rownames(sites),pos=c(3,4,1,2),col="yellow")

if (FALSE) {
# Compute transition object with no depth constraint
	trans1 <- trans.mat(hawaii)

# Compute transition object with minimum depth constraint:
# path impossible in waters shallower than -200 meters depth
	trans2 <- trans.mat(hawaii,min.depth=-200)

# Computes least cost distances for both transition matrix and plots the results on the map
	out1 <- lc.dist(trans1,sites,res="path")
	out2 <- lc.dist(trans2,sites,res="path")
	lapply(out1,lines,col="yellow",lwd=4,lty=1) # No depth constraint (yellow paths)
	lapply(out2,lines,col="red",lwd=1,lty=1) # Min depth set to -200 meters (red paths)

# Computes and display distance matrices for both situations
	dist1 <- lc.dist(trans1,sites,res="dist")
	dist2 <- lc.dist(trans2,sites,res="dist")
	dist1
	dist2

# plots the depth profile between location 1 and 3 in the two situations
	dev.new()
	par(mfrow=c(2,1))
	path.profile(out1[[2]],hawaii,pl=TRUE,
                 main="Path between locations 1 & 3\nProfile with no depth constraint")
	path.profile(out2[[2]],hawaii,pl=TRUE,
                 main="Path between locations 1 & 3\nProfile with min depth set to -200m")
}