[Bug] `TerrainLayer` zooming, `TerrainExtension` draping

[charlieforward9]

Description

PathLayers draped onto TerrainLayer via the TerrainExtension have a resolution-related conflict at high zooms. The less coordinates in the PathLayer, the worse the bug seems to be.

Flavors

• Script tag
• React
• Python/Jupyter notebook
• MapboxOverlay
• GoogleMapsOverlay
• CARTO
• ArcGIS

Expected Behavior

TerrainExtension to work harmoniously across all zoom levels with PathLayer (including TripsLayer)

Steps to Reproduce

https://codepen.io/charlieforward9/pen/dPGjPjY

Environment

• Framework version: deck.gl@8.9 - 9.3-alpha.1
• Browser: Chrome
• OS: MacOS Tahoe

Logs

A glorious discussion about hubble.gl, noodles.gl and nebula.gl with @akre54 ultimately led him to recommending a hand from @felixpalmer on this Terrain specific task.

Thank you all!

[akre54]

It seems to be an issue with 3d tiles at high zoom / high lod.

You might be able to use the polygonOffset prop (see docs) and multiply your layerIndex by some value. You could try switching to offset mode and just using altitude, but if you want that drape texture behavior you'll need to work around the limitations. Maybe you want to use raycasting. Lastly, you can try switching the layer order, which affects the draw order. Something like this may or may not be impacted by the z-buffer.

[charlieforward9]

You might be able to use the polygonOffset prop (see docs) and multiply your layerIndex by some value.

Updated the codepen with my attempt, no change.

You could try switching to offset mode and just using altitude

This wont work for my use case

Maybe you want to use raycasting.

I am not familiar with this strategy, would be happy to dig in deeper once I have itemized and managed all of my other issues with Terrain, Globe and deck rendering.

Lastly, you can try switching the layer order, which affects the draw order.

All else the same, switching layer order hides the PathLayer altogether.

Thanks for all the feedback Adam

[charlieforward9]

In addition to the aforementioned, I am having these visual challenges with the TerrainLayer + TerrainExtension integration:

Terrain.fly-In.+.draping.conflict.+.missing.tiles.mov

When zooming in from afar with 'strategy': 'no-overlap' or best-available, the lower zoom tiles are textured with the draped TripLayer, and these textures persist even when zoomed into a higher level. Using the never strategy resolves this, but this strategy obviously comes at a UX cost in other areas.

TerrainLayer.tile.missing.issue.with.strategy.never.mov

Finally, notice how tiles are missing when a pitch is applied (same video with 'strategy': 'never', slightly dragging the viewport usually fixes this, but first impressions are important.

With my naive knowledge of the lower level systems, my only proposal is to add more pitch & zoom-driven intelligence to the TerrainLayer & TerrainExtension integrations

[charlieforward9]

@felixpalmer the PR that was just merged looks unrelated to this bug, can you verify this or explain how this solves the problem? Thanks.

[felixpalmer]

You're right, I don't know why it was tagged with this issue

[charlieforward9]

Still having difficulty with this - this geojson layer is a downsampled line and it look like the defined coordinates are draped properly but the interpolated edges do not conform to the terrain.

Even on 'flat' ground these layers struggle to achieve full visibility.

I will also note that I am passing this through noodles.gl graph as my 'layer state manager', but I doubt that has an impact.

Screen.Recording.2026-01-24.at.6.08.49.PM.mov

[felixpalmer]

@charlieforward9 I've done a number of fixes to the terrain code, is this issue still relevant?

[charlieforward9]

Bumped codepen to 9.3-alpha.1 and still seeing it. Updated description.

9.3-drape-zoom-issue.mov