https://extensions.sketchup.com/extension/33407317-e23a-40b9-8827-55aca1a198fd/eneroth-fog-tool
Set fog start and fog end (where model can no longer be seen) from either points in model or exact lengths.
A typical use is to add depth to parallel projection drawings, but it can also be used for height maps.
Activated from Tools > Fog Tools.