Grades every road: node heights relaxed so no edge is steeper than maxGrade, then each edge
sampled every step metres, clamped to the grade limit from both ends and smoothed. Bridges arch
over the water instead. Writes node.y and returns one profile per edge (by edge id).
Grades every road: node heights relaxed so no edge is steeper than
maxGrade, then each edge sampled everystepmetres, clamped to the grade limit from both ends and smoothed. Bridges arch over the water instead. Writesnode.yand returns one profile per edge (by edge id).