mapiso {mapiso}

Create Contour Polygons from Regular Grids

Description

Regularly spaced grids containing continuous data are transformed into contour polygons. A grid can be defined by a data.frame (x, y, value), an sf object, a terra SpatRaster or SpatVector.

Usage

mapiso(x, var, breaks, nbreaks = 8, mask, coords, crs)

Arguments

x

a data.frame, an sf object or a SpatRaster

var

name of the variable, for data.frames and sf objects only

breaks

list of break values (default to equal interval)

nbreaks

number of classes

mask

an sf object or SpatVector of polygons or multipolygons. mask is used to clip contour polygons

coords

names of the coordinates variables (e.g. c("lon", "lat")), for data.frames only

crs

CRS code (e.g. "epsg:2154"), for data.frames only.

Value

The output is an sf object of polygons (or a SpatVector if x is a SpatVector). The data.frame contains three fields: id (id of each polygon), isomin and isomax (minimum and maximum breaks of the polygon).

Examples

# sf, using a mask
library(sf)
s <- st_read(system.file("gpkg/elevation.gpkg", package = "mapiso"),
  layer = "elevation", quiet = TRUE
)
m <- st_read(system.file("gpkg/elevation.gpkg", package = "mapiso"),
  layer = "com", quiet = TRUE
)
isos <- mapiso(
  x = s, var = "elevation",
  mask = m
)
plot(isos)

# data.frame, using user breaks values
d <- read.csv(system.file("csv/elevation.csv", package = "mapiso"))
bks <- c(98, 100, 150, 200, 250, 300, 350, 400, 412.6)
isod <- mapiso(
  x = d, var = "elevation",
  breaks = bks, coords = c("x", "y"), crs = "epsg:2154"
)
plot(isod)
if (require(mapsf, quietly = TRUE)) {
  mf_map(isod, "isomin", "choro", breaks = bks, leg_title = "Elevation")
}
## Not run: 
if (require(terra, quietly = TRUE)) {
  # terra SpatRaster
  r <- rast(system.file("tif/elevation.tif", package = "mapiso"))
  isor <- mapiso(x = r)
  plot(r)
  plot(st_geometry(isor), add = TRUE, col = NA)
  # terra SpatVector
  s_terra <- vect(s)
  m_terra <- vect(m)
  isost <- mapiso(
    x = s_terra, var = "elevation", mask = m_terra
  )
  plot(isost)
}

## End(Not run)