Calc_network_catchment example issue

[edclay123]

Hi guys thanks for your work on this package, it is very useful.

I was trying to reproduce the calc_network_catchment example included in the 'stplanr: A Package for Transport Planning' pdf but there seems to be an issue with overlapping buffers. This also affects the calculating the number of people in the catchment as it is larger under the calc_network_catchment function than calc_catchment, leading me to believe there is double counting.

I have included the code below so it is quicker to test/reproduce.

library(stplanr)

data_dir <- system.file("extdata", package = "stplanr")
unzip(file.path(data_dir, 'smallsa1.zip'))
unzip(file.path(data_dir, 'testcycleway.zip'))
sa1income <- rgdal::readOGR(".", "smallsa1")
testcycleway <- rgdal::readOGR(".", "testcycleway")
# Remove unzipped files
file.remove(list.files(pattern = "^(smallsa1|testcycleway).*"))

catch800m <- calc_catchment(
polygonlayer = sa1income,
targetlayer = testcycleway,
calccols = c('Total'),
distance = 800,
projection = 'austalbers',
dissolve = TRUE
)

plot(sa1income, col = "light grey")
plot(catch800m, col = rgb(1, 0, 0, 0.5), add = TRUE)
plot(testcycleway, col = "green", add = TRUE)

unzip(file.path(data_dir, 'sydroads.zip'))
sydroads <- rgdal::readOGR(".", "roads")
file.remove(list.files(pattern = "^(roads).*"))
sydnetwork <- SpatialLinesNetwork(sydroads)

netcatch800m <- calc_network_catchment(
sln = sydnetwork,
polygonlayer = sa1income,
targetlayer = testcycleway,
calccols = c('Total'),
maximpedance = 800,
distance = 100,
projection = 'austalbers'
)

plot(sa1income, col = "light grey")
plot(catch800m, col = rgb(1, 0, 0, 0.5), add = TRUE)
plot(netcatch800m, col = rgb(0, 0, 1, 0.5), add = TRUE)
plot(testcycleway, col = "green", add = TRUE)

sum(catch800m$Total)
sum(netcatch800m$Total)