Module remove_spikes 

remove_spikes(&mut g) — drop collinear-and-reversed vertices.

Mirrors boost::geometry::remove_spikes from boost/geometry/algorithms/remove_spikes.hpp. The predicate is Boost’s point_is_spike_or_equal, and the or_equal half carries its weight: a triple (a, b, c) qualifies when (b-a) × (c-b) == 0 (collinear) and (b-a) · (c-b) <= 0, which covers both a reversal and a zero-length step — that is, a repeated vertex. The middle vertex b is removed; the walk repeats until nothing qualifies, because collapsing one spike can create a new one at the now-adjacent pair, and peeling a spike off a ring routinely leaves a repeated vertex behind.

Per-kind:

• Linestring, Ring → spike-walk the backing Vec<P>
• Polygon → walk outer + every inner ring
• MultiPolygon → walk each member

Cartesian-only: the collinearity / reversal predicate is the 2D cross/dot product. Spherical / geographic spike detection needs angle-aware predicates; deferred until a downstream caller appears.

Functions

remove_spikes

Remove spikes from g in place.