Get area of a closed outline

Calculate the area enclosed by a shape using the shoelace formula.

Usage

get_area(x, ..., .cols = NULL)

Arguments

x

A matrix (nx2), list of matrices, or tibble with coo columns.

...

Additional arguments (reserved for future use).

.cols

Column name(s) to process when x is a tibble. If NULL, automatically detects columns containing coo objects.

Value

• If x is a single matrix: returns a numeric scalar

• If x is a list: returns a numeric vector

• If x is a tibble: returns a numeric vector extracted from coo column

Details

Uses the shoelace formula (also called surveyor's formula) to compute area. The outline is automatically treated as closed (first point connects to last).

For tibbles, this function extracts values without modifying the tibble. Use within mutate() to add as a column, or use measure("area") for convenience.

See also

measure() for adding measurement columns; get_perim() for perimeter

Examples

get_area(shapes$cat)
#> [1] 14125.5
get_area(shapes)
#> $cat
#> [1] 14125.5
#> 
#> $dog
#> [1] 14907.5
#> 
#> $heart
#> [1] 24277
#> 
#> $leaf2
#> [1] 16905.5
#> 

# Extract from tibble
areas <- get_area(bot)

# Add to tibble
bot$area <- get_area(bot)

# Or use measure() for convenience
bot %>% measure("area")
#> # A tibble: 40 × 5
#>    coo       type   dummy    area coo_area
#>    <out>     <fct>  <fct>   <dbl>    <dbl>
#>  1 (138 x 2) whisky a     234515   234515 
#>  2 (168 x 2) whisky a     201056.  201056.
#>  3 (189 x 2) whisky a     119460.  119460.
#>  4 (129 x 2) whisky a     119568.  119568.
#>  5 (152 x 2) whisky a     165736.  165736.
#>  6 (161 x 2) whisky a     114015   114015 
#>  7 (124 x 2) whisky a     149503   149503 
#>  8 (126 x 2) whisky a     147642.  147642.
#>  9 (183 x 2) whisky a     130178.  130178.
#> 10 (193 x 2) whisky a     219548   219548 
#> # ℹ 30 more rows