explorer: fix halo cutoff over terrain (disableDepthTestDistance)#181
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The white halos added in isamplesorg#180 made a pre-existing terrain depth-test artifact visible: dots positioned at altitude=0 get partly (or entirely) occluded by Cesium World Terrain wherever land elevation rises. Without halos, the truncation read as a smaller dot. With halos, the white ring exposes the cut as a crescent — and over higher terrain, the whole sprite disappears. Fix: add `disableDepthTestDistance: Number.POSITIVE_INFINITY` to all three PointPrimitive add() sites (h3Points x2 + samplePoints), matching the existing pattern used by `pointLabel` (line 843) — points render always-on-top regardless of intervening terrain. Reported view: explorer.html#v=1&lat=33.27&lng=-86.24&alt=311435 (Birmingham AL hill country). Verified locally — dots render as full circles; previously- missing dots over higher terrain are visible again. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This was referenced May 9, 2026
explorer: halo crescents / disappearing dots over hilly terrain (root cause not yet identified)
#185
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rdhyee
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May 10, 2026
…terrain (closes #185) (#198) Cluster and sample point primitives are placed at altitude=0 (the WGS84 ellipsoid surface). With Cesium world terrain enabled, terrain mesh in hilly regions (Troodos in Cyprus, hill country around Birmingham AL, etc.) rises hundreds to thousands of meters above ellipsoid — so points at altitude=0 are physically *underground* in those regions and get depth-culled by Cesium's standard per-pixel depth test. The fix is one new property at each of the three .add() call sites: disableDepthTestDistance: POINT_DEPTH_TEST_DISTANCE // 2.0e6 = 2,000 km Bypass scope: only when the camera is closer than 2,000 km, which covers every realistic interactive altitude (point mode <120 km, res8 cluster up to ~300 km, res6 up to ~3,000 km — the upper end is technically outside the bypass but at that altitude dots are tiny anyway). Why bounded (2.0e6) and not POSITIVE_INFINITY: PR #181 used Infinity and caused back-side-of-globe primitive bleed-through plus broke pickability (was reverted via #183). A 2,000 km bound preserves globe-ellipsoid occlusion at long range while bypassing terrain occlusion at every interactive zoom. Hypothesis source: Codex review of #185 identified sea-level placement as the most likely root cause. Confirmed experimentally by runtime- patching the live deploy: T0 baseline (no fix) Cyprus interior: ~0 dots T1 swap to EllipsoidTerrainProvider minor improvement T2 raise primitives to height=5000m significant improvement T3 disableDepthTestDistance: 2.0e6 (this PR) significant, equivalent to T2, no back-side bleed Closes #185. Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
Hotfix for the halo regression introduced in #180.
The white halos exposed a pre-existing Cesium terrain depth-test artifact: PointPrimitives are positioned at altitude=0, so wherever Cesium World Terrain has elevation, the front face of the terrain mesh occludes part of the sprite. Without halos, that truncation read as a slightly smaller dot. With halos, the white ring made the cut glaringly obvious — appearing as crescents — and over higher terrain the sprite vanishes entirely.
Reported view:
explorer.html#v=1&lat=33.2706&lng=-86.2375&alt=311435(Birmingham, AL hill country) — many dots showed only as half-moon halos or were entirely missing.Fix
Add
disableDepthTestDistance: Number.POSITIVE_INFINITYto all threePointPrimitive.add()sites (h3Points x2 cluster-mode + samplePoints x1). This matches the existing pattern already used bypointLabelat line 843 — points render always-on-top regardless of intervening terrain.Trade-off
With depth test off, points on the far side of the globe could in principle bleed through. In practice at the zoom levels users hit (regional → world), the cluster aggregation hides this, and Cesium's frustum culling still removes truly back-facing primitives. Standard fix per Cesium docs.
Verified locally
quarto render+ Playwright at the reported camera (lat=33.27, lng=-86.24, alt=311km):Test plan
https://isamples.org/explorer.html#v=1&lat=33.2706&lng=-86.2375&alt=311435&heading=360.0and confirm full-circle dots replace the previous crescents🤖 Generated with Claude Code