[narag]

I expect if astronauts aboard HLS lose their altimeter they'd have to abort the landing immediately -- to proceed without it would be the height of recklessness.

In addition to the obvious, it should be taken into account that the absence of atmosphere makes very difficult to assess distance and scale. Videos of approach seem like a fractal browser.

[WalterBright]

You can judge height by the distance to your shadow.

[wongarsu]

Also the rocks suddenly start rendering once you are within 500m of the surface

[narag]

Indeed. But only when you're close to the ground and then it could be too late.