RRT: Safe Nodes with an Edge Through an Obstacle
Adds segment collision, robot radius and repeatable seeds to path-planning verification.
Project: Python RRT and RRT* Path Planning Demonstration
Symptom: New nodes were outside obstacles, but their connecting edges crossed obstacles.
Hypothesis: Collision checking covered discrete endpoints but not the full extension edge.
Investigation: Reproduced with fixed seeds across default, narrow and sealed maps and compared GUI with headless output.
Root cause: Endpoint-only checks did not establish edge safety, and robot radius was missing.
Fix: Checked every segment, inflated obstacles for clearance and propagated subtree cost after RRT* rewiring.
Lesson: Planning tests need edge collision, impossible maps and repeatable seeds rather than one successful animation.