terrain_project

A curve drives the ground: the points of the curve a geometry holds ride op_payload, and every cell's height is banded by its ground-plane distance to the resulting polyline — one dispatch, so the channel it cuts has no seam where a chain of stamps would have met.

Inside width, falling to zero across falloff metres beyond it, a cell blends toward a target height:

• useCurveHeight set: the curve's own y at the nearest point on the polyline — a road or a riverbed that follows the curve's authored elevation.
• otherwise: fromHeight .. toHeight, interpolated by how far along the polyline (ground-plane arc length, 0 at the first control point, 1 at the last) the nearest point falls — a ramp that runs the whole curve's length in one dispatch instead of one ramp stamp per segment.

blend decides how the target height meets what the layer already holds: replace, add, max, or min.

The polyline is open — segment i to i+1 for every consecutive pair of the curve's sampled points — and distance and arc length are both measured in the ground plane; a point's height does not distort either.