findblocks_bc {rasterbc}

Identify NTS/SNRC codes covering a given geometry

Description

Data layers for the province of BC are split according to the mapsheet coding system used by Canada's NTS/SNRC. This function identifies mapsheets intersecting with the geographical extent of geo.

Usage

findblocks_bc(geo = NULL, type = "character")

Arguments

geo

A point, line, or polygon object of class sfc, or a character vector of 4-character codes

type

character, the object type to return, either 'character' or 'sfc'

Details

When type='character', the function returns the 4-character NTS/SNRC codes corresponding to mapsheets that intersect with the input geometry. When type='sfc', the function returns the mapsheet polygons themselves.

geo=NULL (the default) indicates to return all mapsheet codes/polygons. Non-NULL geo must either be a character vector of codes, or else an sfc class object having a coordinate reference system ('crs' attribute) defined. If geo intersects with none of the BC mapsheets, (or contains unknown NTS/SNRC codes) the function returns NULL.

Value

either a character vector or an sfc object (see details)

Examples

# list all mapsheet codes then print the corresponding sfc object
findblocks_bc()
findblocks_bc(type='sfc')

# define an example point by specifying latitude and longitude (in WGS84 reference system)
input.point = sf::st_point(c(x=-120, y=50)) |> sf::st_sfc(crs='EPSG:4326')

# this point lies at the intersection of four mapsheets, which are in Albers projection
blocks = findblocks_bc(input.point, type='sfc')
blocks |> sf::st_geometry() |> plot()
sf::st_transform(input.point, crs='EPSG:3005') |> plot(add=TRUE)
blocks |> sf::st_geometry() |> sf::st_centroid() |>
    sf::st_coordinates() |> text(labels=blocks$NTS_SNRC)

# nudge the point slightly so it intersects with only one mapsheet
input.point = sf::st_point(c(x=-120.1, y=50.1)) |> sf::st_sfc(crs='EPSG:4326')
blocks |> sf::st_geometry() |> plot()
sf::st_transform(input.point, crs='EPSG:3005') |> plot(add=TRUE)
blocks |> sf::st_geometry() |> sf::st_centroid() |>
   sf::st_coordinates() |> text(labels=blocks$NTS_SNRC)
findblocks_bc(input.point)

# make a polygon (circle) from the point and repeat
if( requireNamespace('units', quietly = TRUE) ) {
input.polygon = input.point |> sf::st_buffer(units::set_units(10, km))
blocks |> sf::st_geometry() |> plot()
sf::st_transform(input.polygon, crs='EPSG:3005') |> plot(add=TRUE)
blocks |> sf::st_geometry() |> sf::st_centroid() |>
   sf::st_coordinates() |> text(labels=blocks$NTS_SNRC)
findblocks_bc(input.polygon)
}

# geo can be a character vector of codes
input.codes = c('093A', '093I', '104O')
findblocks_bc(input.codes, type='sfc')