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Create channel cross sections object

xt_sxc.Rd

Channel cross sections are a lightweight wrapper on sf geometries (sfc objects), specifically a collection of line segments. This means that you can use functions from sf to manipulate these objects whenever special cross section methods do not exist.

Usage

xt_sxc(x, ...)

Arguments

x

Object to create cross sections out of. Can be a vector of (positive) widths if the spatial orientation is not important; can be line segments created using the sf package.

...

Optional arguments passed to sf::st_sfc() relating to the geometrical properties of the cross sections, such as crs.

Value

A channel cross section object, with class "sxc", which is a subclass of sf's "sfc_LINESTRING" class. The nomenclature is inspired by the sf package, so that "sxc" stands for "spatial cross-section column".

Examples

# Create cross sections without worrying about spatial orientation.
(a <- xt_sxc(1:3))
#> Simple cross section collection with 3 cross sections
#> Geometry set for 3 features 
#> Geometry type: 
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: 1 xmax: 3 ymax: 3
#> CRS:           NA
#> LINESTRING (0 1, 1 1)
#> LINESTRING (0 2, 2 2)
#> LINESTRING (0 3, 3 3)
print(a)
#> Simple cross section collection with 3 cross sections
#> Geometry set for 3 features 
#> Geometry type: 
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: 1 xmax: 3 ymax: 3
#> CRS:           NA
#> LINESTRING (0 1, 1 1)
#> LINESTRING (0 2, 2 2)
#> LINESTRING (0 3, 3 3)

# Create cross sections from sf line segments, this time with a
# coordinate reference system. Note that even though we input a
# multilinestring, sxchan parses it into linestrings, so that each
# cross section is a linestring.
library(sf)
seg <- st_multilinestring(list(
  matrix(c(0, 1, 0, 1), ncol = 2),
  matrix(c(0, 1.5, -0.5, 0), ncol = 2)
))
b <- xt_sxc(seg, crs = 3005)
plot(b)


# Because these objects are just sxc objects from the sf package,
# we can manipulate them with sf.
# - Subset to grab individual cross section line segments:
b[[1]]
#> LINESTRING (0 0, 1 1)
b[[2]]
#> LINESTRING (0 -0.5, 1.5 0)

# - Add arbitrary features to the cross sections.
(b2 <- st_sf(b, roughness = 0.1, swimmability = c(4, 2)))
#> Simple cross section collection with 2 cross sections
#> Simple feature collection with 2 features and 2 fields
#> Geometry type: 
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: -0.5 xmax: 1.5 ymax: 1
#> Projected CRS: NAD83 / BC Albers
#>   roughness swimmability                          b
#> 1       0.1            4      LINESTRING (0 0, 1 1)
#> 2       0.1            2 LINESTRING (0 -0.5, 1.5 0)

# - Want to add / change more columns / features? It's just a data frame:
b2$rockiness <- c(1, 1.1)
b2
#> Simple cross section collection with 2 cross sections
#> Simple feature collection with 2 features and 3 fields
#> Geometry type: 
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: -0.5 xmax: 1.5 ymax: 1
#> Projected CRS: NAD83 / BC Albers
#>   roughness swimmability                          b rockiness
#> 1       0.1            4      LINESTRING (0 0, 1 1)       1.0
#> 2       0.1            2 LINESTRING (0 -0.5, 1.5 0)       1.1
plot(b2)


# - The geometry column is still a cross section object
st_geometry(b2)
#> Simple cross section collection with 2 cross sections
#> Geometry set for 2 features 
#> Geometry type: 
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: -0.5 xmax: 1.5 ymax: 1
#> Projected CRS: NAD83 / BC Albers
#> LINESTRING (0 0, 1 1)
#> LINESTRING (0 -0.5, 1.5 0)