getGeoDist: Function to calculate geodesic distances

In lindesaysh/MRSea: Spatially adaptive regression splines using SALSA

Function to calculate geodesic distances

Description

Function to calculate geodesic distances

Usage

getGeoDist(xygrid, polys, datalocations = NULL, plot.transition = TRUE)

Arguments

xygrid	Regular grid of x and y coordinates, must have an extent greater than that of datalocations if specified.
polys	Either a single polygon (defined by a dataframe with x and y) or a list object containing multiple polygons that define exclusion zones.
datalocations	data frame of x and y coordinates of locations to calculate distances between. Default = NULL, in which case distances are returned between locations in xygrid
plot.transition	(default=TRUE). Logical stating whether to plot the transition matrix. Useful to see if the boundaries are being obeyed.

Details

Using the raster, spancs and gdistance packages to calculate the geodesic distance between pairs of points. The polygons define the areas that an animal/object cannot be. E.g. Land if the animal is a marine mammal.

The object returned is a matrix of distances between pairs of points and the x,y coordinates of each pair of points.

Examples

Nx=100
Ny=100

xygrid<-expand.grid(x=1:Nx, y=1:Ny)

# make exclusion polygon,
bnd<-data.frame(x=c(78  ,79, 52, 53 , 82 , 82, 100, 103 ,104 , 70), 
y= c( 99  ,65 , 66 , 43 , 42 , 16, 19, 16 ,102 ,105))
bnd2<-data.frame(x= c(37 ,54 ,55, 37), y=c(35 ,35, 17, 18))

geodistsoutput<-getGeoDist(xygrid=xygrid, polys=list(bnd, bnd2))

# show on plot
i=2150
a.dist.mesh = data.frame(geodistsoutput$xydata, value=geodistsoutput$distance[i,])
iLCdsitance = rasterFromXYZ(a.dist.mesh)
plot(iLCdsitance, col=topo.colors(100))
points(geodistsoutput$xydata[i,1],geodistsoutput$xydata[i,2])
polymap(bnd, add=T)
polymap(bnd2, add=T)

lindesaysh/MRSea documentation built on April 5, 2024, 4:39 p.m.