This function gives access to the underlying values defining the geometries
in a vector. As such they return the same information as calling
`as.matrix()`

on a geometry vector except the return value is kept as an
exact numeric and that you can extract from single elements if the
cardinality of the geometry exceeds 1.

```
parameter(x, ...)
# S3 method for euclid_geometry
parameter(x, which, element = NA, ...)
# S3 method for euclid_affine_transformation
parameter(x, i, j, ...)
```

- x
A geometry vector

- ...
parameters to pass on

- which
Either a name or the index of the definition to extract, as matched to

`definition_names(x)`

- element
For geometries with a cardinality above 1, which element of the geometry should the definition be extracted for. If

`NA`

the definition for all elements will be returned and the length of the returned vector will be`sum(cardinality(x))`

(matching the return of`as.matrix(x)`

)- i, j
The row and column of the cell in the transformation to fetch.

An exact_numeric vector

Other Geometry methods:
`euclid_geometry`

,
`vertex()`

```
# Get squared radius of circle
circ <- circle(point(4, 7), 25)
parameter(circ, "r2")
#> <exact numerics [1]>
#> [1] 25
# Get all the x values from the source of segments
s <- segment(point(sample(10, 4), sample(10, 4)),
point(sample(10, 4), sample(10, 4)))
parameter(s, "x", 1L)
#> <exact numerics [4]>
#> [1] 1 7 4 6
# Get y for all subelements
parameter(s, "y")
#> <exact numerics [8]>
#> [1] 8 1 9 2 4 4 5 3
# Extract cell values from transformation matrices
m <- affine_rotate(c(pi/2, pi/3))
parameter(m, 1, 2)
#> <exact numerics [2]>
#> [1] -1.0000000 -0.8660254
```