| """Extract causal events (collisions, starts/stops of motion) from a trajectory. |
| |
| This is what makes question generation *grounded*: every question/answer is |
| derived from events that verifiably happened in the recorded physics rollout. |
| """ |
|
|
| import numpy as np |
|
|
| from . import config |
|
|
|
|
| def extract_events(states, collisions, wall_hits, n): |
| """Args: |
| states: (T, n, 4) per-frame (x, y, vx, vy) |
| collisions: [(t, i, j)] substep-level contact log |
| wall_hits: [(t, i, axis, side)] |
| n: number of objects |
| |
| Returns dict with: |
| collisions: [{frame, objects:[i,j]}] grouped collision events |
| starts: {obj_idx: [frames]} times each object starts moving |
| stops: {obj_idx: [frames]} |
| initially_moving: [obj_idx] |
| moving: (T, n) bool mask |
| speeds: (T, n) |
| """ |
| T = states.shape[0] |
| speeds = np.linalg.norm(states[:, :, 2:], axis=-1) |
| moving = speeds > config.MOVE_THRESH |
|
|
| |
| grouped = [] |
| for (t, i, j) in sorted(collisions, key=lambda c: c[0]): |
| if grouped and grouped[-1]["objects"] == [i, j] and \ |
| t - grouped[-1]["end"] <= config.MIN_EVENT_GAP_FRAMES: |
| grouped[-1]["end"] = t |
| else: |
| grouped.append({"frame": t, "end": t, "objects": [i, j]}) |
| collision_events = [{"frame": g["frame"], "objects": g["objects"]} for g in grouped] |
|
|
| |
| starts, stops, initially_moving = {}, {}, [] |
| min_run = config.MIN_RUN_FRAMES |
| for o in range(n): |
| m = moving[:, o] |
| sts, sps = [], [] |
| t = 0 |
| while t < T: |
| if m[t]: |
| t2 = t |
| while t2 < T and m[t2]: |
| t2 += 1 |
| if t2 - t >= min_run: |
| if t == 0: |
| initially_moving.append(o) |
| else: |
| sts.append(t) |
| sps.append(t2) |
| t = t2 |
| else: |
| t += 1 |
| starts[o] = sts |
| stops[o] = [s for s in sps if s < T - 1] |
|
|
| return { |
| "collisions": collision_events, |
| "starts": starts, |
| "stops": stops, |
| "initially_moving": sorted(initially_moving), |
| "moving": moving, |
| "speeds": speeds, |
| "wall_hits": wall_hits, |
| } |
|
|
