networkdistance | R Documentation |
Simple network computation of distance between points along linear landscape features (e.g. rivers).
networkdistance(xy1, xy2, geometry)
xy1 |
2-column matrix or dataframe |
xy2 |
2-column matrix or dataframe |
geometry |
‘linearmask’ object |
networkdistance
computes the distance in metres between the
points in xy1
and the points in xy2
. The geometry
is a linearmask; if it is missing then it takes the value of xy2
,
which then of course must be a full linearmask. A network is taken from
the ‘graph’ attribute of geometry
or (if necessary) constructed
from the linearmask ‘on the fly’, joining any points closer than
(spacingfactor
x spacing(geometry)
). Points in xy1
and xy2
are first snapped to the nearest point in
geometry
. The computed distance is the sum of the graph's edge
weights along the shortest path joining two points.
The commonest use of networkdistance
is to calculate distances
between detectors (traps) and points on a linear mask. In this case it
is sufficient to provide two arguments only, as xy2
serves as
both destination and geometry.
networkdistance
meets the requirements for a user-defined
distance function (userdist) in secr. No parameter is estimated.
Use showpath
to check network distances interactively.
networkdistance
–
given k
detectors and m
mask
points, a k
x m
matrix of distances.
If called with no arguments networkdistance
returns a
zero-length character vector.
read.linearmask
, showpath
,
asgraph
x <- seq(0, 4*pi, length = 200)
xy <- data.frame(x = x*100, y = sin(x)*300)
mask <- read.linearmask(data = xy, spacing = 20)
trps <- make.line(mask, n = 15, startbuffer = 1000, by = 30)
## networkdistance; geometry in 'mask'
d <- networkdistance (trps, mask, mask)
dim(d)
head(d)
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