vector_segments function

Functions for overlaying networks on shapefiles

The function vector_segments and assign_pa_to_segments were written to facilitate the generation of plots (including ggplots) that overlay user defined digraphs (based on arc designations) on GIS shapefiles or other tightly packed cartesian coordinate structures.

vector_segments(sf.coords, node.coords, realign = TRUE, arcs, arc.symbol = " --> ", 
nneighbors = 40, remove.duplicates = FALSE)

assign_pa_to_segments(input, n, arc.pa, datetime = NULL)

Arguments

• sf.coords: A two column dataframe containing shapefile Cartesian coordinates (or other tightly packed Cartesian coordinates, see Examples). The first column should define x locations and the second column define y locations.
• node.coords: A two column dataframe containing network node Cartesian coordinates, with the first column defining x location and the second column defining y location. The coordinates should use the same coordinate system as sf.coords, e.g., UTM easting and northing, longitude and latitude, etc. The row.names attribute should contain the correct node names (i.e., they should correspond to names used in the argument arcs.
• realign: Logical. If node.coords do not exist in sf.coords should they be assigned to the closest location in sf.coords? The default option realign = TRUE is strongly reccomended, and may be set permenantly in later versions of vector_segments.
• arcs: A character vector of arc names in the network. In particular, designations of nodes which serve arcs bounds, seperated by a user-defined arc.symbol. For example, to designate the arc $\overrightarrow{uv}$ using the arc.symbol -->, I would use: u --> v. Node names used to define arcs in the character vector should correspond to those in row.names(node.coords).
• arc.symbol: A symbol indicating the directional arc connecting two nodes. For example, to designate the arc $\overrightarrow{uv}$, the package igraph uses u|v, while streamDAG generally uses u --> v.
• nneighbors: Number of nearest neighbor points to potentially consider as the next point in an evolving arc path.
• remove.duplicates: Logical. For duplicate coordinates, should the second point be removed?
• input: The first argument for assign_pa_to_segments. Ideally, the output from vector_segments. For example, let output <- vector_segments(...), then input = output.
• n: The number of repeated presence/absence timeframe observations for surface water contained in arc.pa.
• arc.pa: An $n \times m$ matrix or dataframe of stream arc surface water presence/absence = $\{0, 1\}$ outcomes, where $n$ denotes the number of observed timeframes in which arcs were observed, and $m$ is the number of arcs. The names of the dataframe should correspond to those given in the arcs argument from vector_segments.
• datetime: Optional unique() time classes corresping to rows in arc.pa.

Details

The function vector_segments assigns network arc designations (from the argument arcs) to shape file coordinates. The function assign_pa_to_segments presence/absence surface water designations to these arcs based on information from arc.pa.

Returns

The function vector_segments creates an object of class network_to_sf. It also returns a list with two components, with only the first being visible. - df: Is a dataframe with four columns: 1) point (referring an original sf.coord location), 2) arc.label, an assigned arc name for the location, 3) x the x coordinates, and 4) y the x coordinates.

• node.coords: Is dataframe with the node.coords for stream arcs. These will have been potentially shifted, if realign = TRUE, hence their inclusion as function output.

The function assign_pa_to_segments returns a dataframe that adds a stream/presence absence column to the to the df dataframe output from vector_segments, based on the argument arc.pa

Author(s)

Ken Aho

Note

The assign_pa_to_segments function will return a warning (but will try to run anyway) if input is not the output from vector_segments.

See Also

spatial.plot

Examples

# Data

sfx <- c(-3,0,1.5,2,2.9,4,5,6)
sfy <- c(5,2,1.7,1.6,1.5,1.4,1.2,1)
sf.coords <- data.frame(x = sfx, y = sfy) 
node.coords <- data.frame(x = c(-2.1,2,4,6), y = c(3.75,1.6,1.4,1))
row.names(node.coords) <- c("n1","n2","n3","n4") # must be consistent with arc names
arc.pa <- data.frame(matrix(ncol = 3, data = c(1,1,1, 0,1,1, 1,1,1, 0,0,1), byrow = TRUE))
names(arc.pa) <- c("n1 --> n2", "n2 --> n3", "n3 --> n4")

# Use of vector_segments
vs <- vector_segments(sf.coords, node.coords, realign = TRUE, names(arc.pa))
vs

# Plotting example
plot(sf.coords, pch = 19, col = c(rep(1,4),rep(2,2),rep(3,2)))

vsd <- vs$df
fal <- as.factor(vsd$arc.label)
lvls <- levels(fal)

for(i in 1:nlevels(fal)){
  temp <- vsd[fal == lvls[i],]
  lines(temp$x, temp$y, col = i) 
}

vs4 <- assign_pa_to_segments(vs, 4, arc.pa)
head(vs4)