Clarification on hover behavior for 3D extrusions (add_fill_extrusion_layer)

[ar-puuk]

Hi everyone,

I’m working with 3D extrusions in mapgl and noticed a discrepancy in how hover effects are triggered between two different apps. I’m trying to understand what controls this behavior so I can implement it consistently.

The Issue

In my current application, the hover highlight seems to trigger based on the 2D base (footprint) of the object rather than the 3D volume. If I hover over the top of a tall building, the highlight doesn't trigger unless my cursor is over the ground coordinates where the building sits.

• Current Behavior: Highlight triggers on the feature's base/ground coordinates (see yellow highlight vs. cursor position).
• Desired Behavior: Highlight triggers on the actual 3D geometry where the mouse is pointing (as seen in Kyle Walker’s example).

Comparison

App Source	Behavior Description	Screenshot
My App	Hover triggers on the base (ground) coordinates. Pointer and highlight are offset.
walkerke's Gist	Hover triggers directly on the 3D body of the feature regardless of the base.

Questions

1. Is this behavior controlled by a specific argument within add_fill_extrusion_layer() or the hover effect settings?
2. Does this depend on the underlying MapLibre/Mapbox GL JS version being used?
3. How can I "enable" the 3D-aware hovering so that the pointer accurately selects the extruded object?

I’ve been referencing this gist for comparison. Any insight into the settings required to achieve the direct 3D hover effect would be greatly appreciated!

[ar-puuk]

Update

After some troubleshooting, I’ve discovered that this behavior is determined by the projection system of the map.

• Globe Projection: Hovering triggers based on the 2D base (footprint). This causes the offset I was seeing, where the highlight only activates if the cursor is over the ground coordinates.
• Planar Projection (e.g., Mercator): Hovering is 3D-aware. The highlight triggers accurately on the volume of the extrusion regardless of the height.

Summary

If you need precise 3D hovering, ensure your map is using a planar projection. While it would be great for the globe projection to support 3D raycasting in the same way, I’m posting this here in case others run into the same confusion.