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zwitschi 5aa883eaff docs: convert all architecture .adoc sections to markdown, prettier-format all .md

- Converted 13 individual .adoc section files to .md via
  asciidoctor→docbook5→pandoc(gfm) + post-processing, placed alongside
  the .adoc sources in Docs/Architecture/
- Rebuilt architecture.md from the individual section .md files
- Ran prettier --write on all .md in the repo (23 files changed):
  normalised table column alignment, trailing whitespace, line breaks
- Added .agents/ to .prettierignore (vendored third-party content)
- All .md now passes prettier --check

2026-11-08 13:33:44 +01:00

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Elevation source — USGS 3DEP 1 m DEM, block window

Field	Value
Source	USGS 3DEP Elevation ImageServer, `elevation.nationalmap.gov`, `/arcgis/rest/services/3DEPElevation/ImageServer/exportImage`
Product	3DEP seamless 1 m (CONUS), raster id 129943
Fetched	2026-11-06 22:59 CET
Request	`f=image&bbox=376100,3774050,376650,3774400&bboxSR=26911&imageSR=26911&size=550,350&format=tiff&pixelType=F32&noData=-9999&interpolation=RSP_BilinearInterpolation`
Bounds (EPSG:26911)	E 376 100 – 376 650, N 3 774 050 – 3 774 400
Bounds (WGS84, approx.)	lat 34.1003 – 34.1032, lon −118.3426 – −118.3370
Grid	550 × 350 px, 1 m pixel, float32, tiled TIFF, nodata −9999
File	`Geo/raw/dem-3dep-1m-26911-2026-11-06.tif`, 984 338 bytes
SHA-256	`e571c14c7230d9048697db2893095e1700468e45d4fccf258ceb4d4e9291bdc5`
Horizontal CRS	EPSG:26911 requested and returned (GeoKey 3072 = 26911, model type projected)
Vertical datum	NAVD88 orthometric — 3DEP CONUS convention; the service does not restate it in the file, so this is a documented assumption
Licence	US Government work, public domain

The window is the block plus a ~100 m margin on the east and ~70 m on the other three sides, which is enough to carry the grade through the junctions at both ends without dragging in the hills north of the boulevard.

Sampling cross-check

The raster is reprojected by the service, not by us, so it was checked against the service's own point query (getSamples) and against the independent point service used in ../verification/2026-11-06-elevation.md:

Point	Raster pixel	Service `getSamples`	Earlier point probe
Hollywood × Highland (origin)	115.911	115.910	115.911
Hollywood × Orange Dr	119.422	119.418	119.418
Mid-block crossing	117.593	—	117.53

Agreement is within 4 cm on the raster side and 6 cm against the point probe, so the file's georeferencing and signage are consistent.

What the window contains

Min 110.46 m, max 127.73 m, mean 117.43 m over the 550 × 350 m window — a 17.28 m spread. That spread is not the street relief: it includes building tops and the rising ground north of the boulevard. The walkable relief measured along the street is 3.94 m (../verification/2026-11-06-elevation.md), and that is the number the demo's ground mesh must honour.

Reading the file

Geo/tools/dem_stats.py parses it with the standard library. GDAL cannot run on the host (its flatpak libraries do not resolve outside the sandbox), and the exported TIFF is tiled, not strip-organised — a strip reader silently scrambles the rows. If another tool misreads it, suspect the tile layout before the data.

Open

Reprojecting is not needed: the service already returned EPSG:26911. Anything that samples this file must assume NAVD88 and treat −9999 as nodata.
The window stops 30 m north of the Chinese Theatre's roof line; if the background massing needs ground beyond it, extend the bbox rather than extrapolating.

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