zwitschi
65fb3759c9
Probe 22 points with the USGS 3DEP point service: walkable surfaces span 115.65-119.59 m, a 3.94 m relief, so elevation data is required by the AGENTS rule. Grade falls ~3.3 m eastward over the 279 m block (1.2%) and the north sidewalk sits 0.4-0.7 m above the south. 3DEP 1 m is public domain and becomes the chosen source; the tile itself is still to be downloaded. Factored the shared OSM helpers into Geo/scripts/osm_common.py so the street profile and the elevation probe read the same geometry.
3.2 KiB
Elevation check — Hollywood Blvd block
Measured 2026-11-06 with Geo/scripts/elevation_probe.py against the USGS Elevation Point Query Service (3DEP, 1 m seamless DEM, raster id 129943). Raw responses: Geo/raw/epqs-2026-11-06.json. Reproduce with:
python3 Geo/scripts/elevation_probe.py Geo/raw/osm-api-map-2026-11-06.osm --workers 5
Heights are orthometric, NAVD88, as published for 3DEP CONUS. They are not ellipsoidal heights and must not be mixed with GPS/ellipsoid values.
Note: the point service answers in 6–8 s per request, so the probe runs requests in parallel and samples a grid rather than a dense sweep.
Grid along the boulevard
Five positions along the 279.4 m block, at the south sidewalk (12.6 m from the centreline), the road centreline, and the north sidewalk (13.6 m).
| Along block | South sidewalk | Centreline | North sidewalk |
|---|---|---|---|
| 0.0 m (Orange Dr) | 118.90 | 119.36 | 119.59 |
| 69.8 m | 118.11 | 118.46 | 118.49 |
| 139.7 m | 116.95 | 117.41 | 117.50 |
| 209.5 m | 116.04 | 116.27 | 116.47 |
| 279.4 m (Highland Ave) | 115.65 | 115.91 | 116.10 |
Crossings: Orange Dr 118.96 m, mid-block 117.53 m, Highland 115.95 m.
What the numbers say
- Longitudinal grade: about 3.3 m of fall over 279 m, roughly 1.2 %, descending eastward toward Highland. That is a real, visible slope for a walking demo, not a rounding artefact: it repeats consistently on all three lines.
- Cross slope: the north sidewalk sits 0.4–0.7 m higher than the south across a 26 m road reserve, which is 1.5–2.5 %. The road drains southward.
- Total relief on walkable surfaces: 3.94 m (115.65 m at the Highland end to 119.59 m at the Orange Drive end).
Decision
AGENTS.md requires separately licensed elevation data unless the DEM shows less than 1 m of variation. Here the variation is 3.94 m, so elevation data is required, and the sampled source already qualifies: USGS 3DEP 1 m DEM is a US Government work in the public domain, so there is no licence conflict and no third-party purchase.
Chosen source: USGS 3DEP 1 m (3DEP seamless, CONUS), reprojected to EPSG:26911 with the origin in ../manifests/local-origin.md, vertical datum NAVD88 recorded.
Consequence for 0.1.0: the demo cannot use a flat ground plane. The street and sidewalks must follow this grade, or the walkable demo will look and feel wrong at the Highland end, where the whole block drops away.
Caveat on building-interior samples
Points inside the hero footprint returned 114.53–117.13 m — a 2.6 m spread within one building outline, which is not ground reference. 3DEP can carry structures and voids there. Those four diagnostic points are excluded from the relief figure; use the street and sidewalk lines, not building interiors, for any ground surface.
Next
- Download the 3DEP tile(s) covering the demo bounds, keep the source file (size is larger than the OSM extract; decide commit vs local-only with a manifest and checksum at that point).
- Reproject to EPSG:26911, clip to the block plus margin, and record the vertical datum and the clip bounds.
- Sample the kerb line and the crossing ramps specifically — the grid above is a street-level average, not a kerb profile.