gis - How to calculate distance matrix using gDistance in R? -


i'd calculate distance polygons. calculate methode, use hausdorff distance. have calculate 2 polygon only. how calculate polygons? need please. source code calculate 2 polygon

library(maptools)

library(rgdal)

shape <- readshapepoly("clipjawa.shp") #load file .shp

pemalang <- shape[1,1] #save coordinates polygon 1 variable pemalang

tegal <- shape[2,1] #save coordinates polygon 2 variable tegal

distance <- gdistance(pemalang,tegal,hausdorff=true)

there several ways approach this, perhaps simplest identify combinations (pairs) of indices of polygons, , apply gdistance each of these combinations.

here's example, calculating hausdorff distances pairs of countries in africa, using wrdl_simpl dataset included maptools.

# load , project data library(maptools) data(wrld_simpl) africa <- sptransform(subset(wrld_simpl, region==2),                        crs('+proj=eqc +lon_0=20.390625'))  # calculate pairs of polygons combns <- t(combn(length(africa), 2))  # split spdf list of spdfs africa.split <- split(africa, seq_len(length(africa)))  # each row of combns, calculate haus. dist. relevant pair of  #  polygons dists <- apply(combns, 1, function(x)    gdistance(africa.split[[x[1]]], africa.split[[x[2]]], hausdorff=true))

you can bind these results matrix of combinations convenience:

hdists <- cbind.data.frame(from=as.character(africa$name[combns[, 1]]),                             to=as.character(africa$name[combns[, 2]]),                             d=dists)  head(hdists)  #                                          d # 1 algeria                           angola 4733071 # 2 algeria                            benin 2807129 # 3 algeria                            congo 4056594 # 4 algeria democratic republic of congo 4532625 # 5 algeria                          burundi 5464898 # 6 algeria                         cameroon 3071739

an alternative approach use outer, should less efficient since calculates distances twice (but directly return distance matrix, might desirable).

outer(africa.split, africa.split, fun = vectorize(function(x, y)     gdistance(x, y, hausdorff=true)))

(updated example)


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