A 3D view draws every level upside down and nothing looks wrong

Symptoms

An editor's "raise" lowers the ground. In the viewer, tall objects hang below the level, but a view from above still shows every road clearly, because the tunnel roofs are drawn under it.

Cause

The viewer's axis convention was chosen from drawings of car models, whose height axis grows downwards, and applied to tracks, whose height axis grows upwards (measured). A level mirrored in height and seen from above looks plausible: an orthographic view of a mirrored scene is a believable picture.

Evidence

From the running game: the race keeps each car's position in the level's coordinates. Over three stretches of POD's Beltane exactly one level face lies under the car, and the car is 0.45 above it (road z 15.0, car 15.45; 0.0 and 0.45; a slope 54.8 to 58.8, car 56.7). A road raised in +z lifted all eight cars in the game. A line follower's Left key turns the car anticlockwise in (x, y) as seen from +z.

What to do

Settle each model kind's axes from the running game before building tools on them: read an object's position from memory over geometry you know (a car on a road, a player on a floor) and find the face under it. Check handedness with a turn: the direction a Left input turns as seen from +up. Store the convention per model kind (POD: tracks up, car models down) and test it (a point with larger height projects higher on screen).

tools/triage/axes.py does the measuring. Give it a memrec recording of something that drives or walks on the level, the level's vertices from the project's reader, and a time span in which it turns left:

./gameframe run axes derived/lap.jsonl derived/track.pts --pos car_x,car_y,car_z --index 0 \
    --scale 1/65536 --left-turn 12:15

It names the up axis and its sign (the object rides a steady height above the surface on that axis only) and the handedness.