Heatmaps are rendered differently with and without 3D terrain active

[sebstryczek]

maplibre-gl-js version:

• 4.7.1
• 5.0.0-pre.10
• probably different versions as well

browser: Chrome Version 131.0.6778.86 (Official Build) (x86_64) (MacOS, Intel)

Steps to Trigger Behavior

1. Add heatmap
2. Switch between 3D terrain active/inactive

Link to Demonstration

1. https://jsbin.com/bekorug/edit?html,js,output - minimal example
2. https://jsbin.com/turikuw/edit?html,js,output - using heatmap-globe-terrain.html

Expected Behavior

Heatmaps are rendered the same (or at least similar) with and without 3D terrain active.

Actual Behavior

1. Heatmaps are rendered differently when 3D terrain is active.
2. Some heatmap areas are not continuous across tile borders when 3D terrain is active (they are not blended).
   3D terrain inactive:
   
   3D terrain active:
   

[HarelM]

Thanks for taking the time to report this issue!
There were some attempts to fix the heatmap in regards to terrain, I'm not sure what was the final outcome.

• See here: Heatmap Fix for 3D terrain #4571

CC: @Samarth1696

[Samarth1696]

This behavior seems to be the default when the heatmap is calculated based on terrain elevation. I think maybe we can keep terrain elevation zero when we have zoomed out to a zoom level with "globe+terrain".