# Query the side of the turn constructed by three consecutive points

Source:`R/geometry_predicates.R`

`geometry_turns.Rd`

In 2D the bend three consecutive points form can be oriented either to the
left or two the right. Asking whether it takes a left turn is equivalent to
asking whether `z`

lies on the positive side of the supporting line of
`x`

->`y`

. euclid provides two predicate functions to check whether left or
right turns are constructed from three given point vectors (note that
collinear points will be `FALSE`

for both predicates). It also provides a
function that calculate turn orientation along a single vector of points. The
result of this are given as: `1`

(left), `0`

(collinear), or `-1`

(right).
Note that the output of `turn_along()`

is two elements shorter than the
input.

## See also

Other Predicates:
`collinear()`

,
`constant_in`

,
`geometry_class`

,
`has_intersection()`

,
`in_order()`

,
`is_degenerate()`

,
`location_predicates`

,
`parallel()`

## Examples

```
p <- point(sample(20, 12), sample(20, 12))
turns_left(p[1:4], p[5:8], p[9:12])
#> [1] TRUE TRUE TRUE FALSE
turn_along(p)
#> [1] -1 1 1 -1 -1 -1 -1 1 1 1
plot(segment(p[-12], p[-1]))
euclid_plot(p[-c(1, 12)][turn_along(p) == 1], pch = 16, col = "firebrick")
euclid_plot(p[-c(1, 12)][turn_along(p) == -1], pch = 16, col = "steelblue")
```