This function calculates the area of integer categories in a primary raster (r1). It can optionally compute an overlay area with a second layer (r2) and/or perform calculations within distinct zones defined by a polygon SpatVector.
Usage
area.calc.flex(
r1,
r2_raster = NULL,
r2_vector = NULL,
threshold = NULL,
zonal_polys = NULL,
id_col = NULL,
omit_zero = TRUE,
unit = "km"
)Arguments
- r1
The primary SpatRaster with integer categories.
- r2_raster
An optional SpatRaster for overlay analysis.
- r2_vector
An optional SpatVector for overlay analysis.
- threshold
A numeric value required to binarize 'r2_raster' if it's continuous.
- zonal_polys
An optional SpatVector for zonal analysis.
- id_col
A string specifying the column in 'zonal_polys'.
- omit_zero
A logical value. If TRUE (default), results for category = 0 are removed.
- unit
A string specifying the area unit ("km", "m", or "ha").
Examples
# \donttest{
library(terra)
# 1) Primary raster (integer categories)
land_cover <- rast(ncol = 30, nrow = 30,
xmin = -50, xmax = -49,
ymin = -15, ymax = -14)
values(land_cover) <- sample(1:3, ncell(land_cover), replace = TRUE)
crs(land_cover) <- "+proj=longlat +datum=WGS84 +no_defs"
# Basic: total area by category
area.calc.flex(land_cover, unit = "km")
#> layer area_id category area_km
#> 1 lyr.1 Total Area 1 4015.385
#> 2 lyr.1 Total Area 2 4161.027
#> 3 lyr.1 Total Area 3 3750.448
# 2) Zonal polygons (two regions)
region1 <- vect("POLYGON ((-50 -15, -49.5 -15, -49.5 -14, -50 -14, -50 -15))")
region2 <- vect("POLYGON ((-49.5 -15, -49 -15, -49 -14, -49.5 -14, -49.5 -15))")
regions <- rbind(region1, region2)
crs(regions) <- crs(land_cover)
regions$region_id <- c("A", "B")
area.calc.flex(
land_cover,
zonal_polys = regions,
id_col = "region_id",
unit = "km"
)
#> layer region_id area_id category area_km
#> 1 lyr.1 A Total Area 1 2014.267
#> 2 lyr.1 A Total Area 2 2146.679
#> 3 lyr.1 A Total Area 3 1802.484
#> 4 lyr.1 B Total Area 1 2001.118
#> 5 lyr.1 B Total Area 2 2014.348
#> 6 lyr.1 B Total Area 3 1947.963
# 3) Overlay raster (binary mask)
protected <- rast(land_cover)
values(protected) <- sample(0:1, ncell(protected), replace = TRUE)
area.calc.flex(
land_cover,
r2_raster = protected,
unit = "km"
)
#> layer area_id category area_km
#> 1 lyr.1 Total Area 1 4015.385
#> 2 lyr.1 Total Area 2 4161.027
#> 3 lyr.1 Total Area 3 3750.448
#> 4 lyr.1 Overlay Area 1 1881.803
#> 5 lyr.1 Overlay Area 2 2027.681
#> 6 lyr.1 Overlay Area 3 2041.098
# }