Negative fill extrusions

[averas]

First things first: Amazing work on the extrusion fills and 3D buildings support!

One thing that immediately struck me given my own use cases: Has negative (below surface level) extrusions been considered? I naïvely tried setting negative values, but that did not render expected results (it seems the extrusions wrapped and the height became very high instead).

Cases where this might be interesting is showing sub-surface shafts or parking areas, or, as in my case, bathymetric levels for lakes.

A potential challenge is how to handle the background layer which will cover anything below what is "surface level" today. Perhaps the background layer could to be rendered at a z-level similar to any locally present negative extrusions.

[mike-marcacci]

That's interesting – perhaps this is more related to terrain elevation (#1489) than building extrusion?

[averas]

@mike-marcacci Ah, yes. Related thread indeed. Probably the bathymetry stuff I mentioned is more of a 3D terrain use case (where you have DEMs spanning over entire regions) while shafts etc. is probably more suited for something like negative extrusions (where you have heights assigned to individual features).

[lbud]

@averas Mapbox GL is fundamentally designed as a 2D map renderer, and renders layers additively, so rendering negative extrusions (cutting into other layers features, rendered to the z0 plane) would be a huge refactor and is not currently on our roadmap. But it does sound like for your use case #1489 may be good ticket to follow :)

[douglasg14b]

With the addition of 3D features, would it be possible to now do these negative extrusions (For example, to make a pit)?

[astojilj]

Reopening this one and we'll take another look.

[iskandari]

In light of the growth of indoor GIS apps, is there a roadmap for enabling negative extrusions below the z0 plane?