ea_homogeneous_area — ea_homogeneous

A function to create a new geometry based on two input geometries. The function is meant to precede ea_spread and to define homogeneous area over which we can spread (i.e. aggregate) indicator values.

Usage

ea_homogeneous_area(
  delineation1,
  delineation2,
  outline,
  keep1 = NULL,
  keep2 = NULL,
  groups
)

Arguments

delineation1: A geometry (sf or stars object)
delineation2: A second, optional, sf object, with the same crs as delineation1.
outline: An optional sf object to mask out areas outside it.
keep1: Column names in delineation1 to keep in the returned object. Only if delineation1 is an sf object.
keep2: Column names in delineation2 to keep in the returned object.
groups: If delineation1 is a stars object, select the attribute that designates the homogeneous areas class.

Value

The function returns an sf object with polygons defined by the intersection of delineation1, delineation2

and outline. Delineation1 can be a raster (stars object), and will then be vectorised, and neighboring cells with identical values will be merged. Delineation1 and delineation2 should normally be completely overlapping, since areas not covered by both layers will be dropped in the output. An optional outline layer can be used to cut away areas, typically areas outside the accounting area.

Examples

data("ex_raster")
data("ex_polygons")
data("accounting_area")
# Example 1: two sf objects
ex1 <- ea_homogeneous_area(ex_polygons,
          accounting_area,
          keep1 = "condition_variable_2",
          keep2 = "name")
#> Warning: attribute variables are assumed to be spatially constant throughout all geometries
#> Warning: repeating attributes for all sub-geometries for which they may not be constant
# Only the names given by `keep1` and `keep2` are retained:
names(ex1)
#> [1] "name"                 "condition_variable_2" "geometry"            
# Example 2: One stars object and one sf object
ex2 <- ea_homogeneous_area(ex_raster,
          accounting_area,
          keep2 = "name",
          groups = values)
#> Warning: repeating attributes for all sub-geometries for which they may not be constant
#> Warning: attribute variables are assumed to be spatially constant throughout all geometries
#> Warning: repeating attributes for all sub-geometries for which they may not be constant
tmap::tm_shape(ex2)+
 tmap::tm_polygons(col = "values")+
tmap::tm_shape(ex2[ex2$name == "Enebakk",])+
   tmap::tm_polygons(col = "blue", border.col = "black")

# Example 3: Example 2 + outline
enebakk <- accounting_area[accounting_area$name == "Enebakk",]
ex3 <- ea_homogeneous_area(ex_raster,
          accounting_area,
          enebakk,
          keep2 = "name",
          groups = values)
#> Warning: repeating attributes for all sub-geometries for which they may not be constant
#> Warning: attribute variables are assumed to be spatially constant throughout all geometries
#> Warning: repeating attributes for all sub-geometries for which they may not be constant
#> Warning: attribute variables are assumed to be spatially constant throughout all geometries
tmap::tm_shape(ex3)+
          tmap::tm_polygons(col = "values")