nhdplusTools (version 0.7.1)

fix_flowdir: Fix flow direction

Description

If flowlines aren't digitized in the expected direction, this will reorder the nodes so they are.

Usage

fix_flowdir(comid, network = NULL, fn_list = NULL)

Value

a geometry for the feature that has been reversed if needed.

Arguments

comid

integer The COMID of the flowline to check

network

sf data.frame The entire network to check from. Requires a "toCOMID" field.

fn_list

list containing named elements `flowline`, `network`, and `check_end`, where `flowline` is the flowline to be checked and `network` the feature up or downstream of the flowline to be checked, and `check_end` is `"start"` or `"end"` depending if the `network` input is upstream (`"start"`) or downstream (`"end"`) of the flowline to be checked. This option allows pre-compilation of pairs of features which may be useful for very large numbers of flow direction checks.

Examples

source(system.file("extdata/sample_data.R", package = "nhdplusTools"))

fline <- sf::read_sf(sample_data, "NHDFlowline_Network")

# We add a tocomid with prepare_nhdplus
fline <- sf::st_sf(prepare_nhdplus(fline, 0, 0, 0, FALSE),
                   geom = sf::st_zm(sf::st_geometry(fline)))

# Look at the end node of the 10th line.
(n1 <- get_node(fline[10, ], position = "end"))

# Break the geometry by reversing it.
sf::st_geometry(fline)[10] <- sf::st_reverse(sf::st_geometry(fline)[10])

# Note that the end node is different now.
(n2 <- get_node(fline[10, ], position = "end"))

# Pass the broken geometry to fix_flowdir with the network for toCOMID
sf::st_geometry(fline)[10] <- fix_flowdir(fline$COMID[10], fline)

# Note that the geometry is now in the right order.
(n3 <- get_node(fline[10, ], position = "end"))

plot(sf::st_geometry(fline)[10])
plot(n1, add = TRUE)
plot(n2, add = TRUE, col = "blue")
plot(n3, add = TRUE, cex = 2, col = "red")