Geometries located in space (all except directions and vectors), have one or
more points supporting it. Those can be extracted with `vertex()`

. For
geometries with a cardinality above one there's a choice of which support
point to extract.

`vertex(x, which = 1L)`

- x
A vector of geometries

- which
An integer vector giving the vertex to extract in cases of higher cardinality geometries

A `euclid_point`

vector matching the dimensionality of x

For geometries that are defined exclusively by points the definition of the
output is straight forward, e.g. for triangles `vertex()`

will extract one
of the corners depending on the value of `which`

. For the other geometries
the output is defined according to the below:

**circles and spheres**: The vertex is the center**rays**: The vertex is the source**lines and planes**: The vertex is an arbitrary point on the geometry

Other Geometry methods:
`euclid_geometry`

,
`parameter()`

```
# Get the source vertex in a segment
s <- segment(point(3, 6), point(1, -7))
vertex(s, 1)
#> <2D points [1]>
#> [1] <x:3, y:6>
# And the target
vertex(s, 2)
#> <2D points [1]>
#> [1] <x:1, y:-7>
# Arguments are recycled
vertex(s, c(1, 2))
#> <2D points [1]>
#> [1] <x:3, y:6>
# Get a point on a line
vertex(line(4, 7, -1))
#> <2D points [1]>
#> [1] <x:1, y:-0.429>
```