Add Ground Zero terrain pipeline and playable assets

2026-05-14 00:09:40 -07:00
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+# Ground Zero DEM Acquisition
+
+## Purpose
+
+This document records the official USGS 3DEP DEM product selected for the Ground
+Zero MVP tile.
+
+## Acquisition Script
+
+```text
+Scripts/acquire_ground_zero_dem.py
+```
+
+The script:
+
+- Reads the Ground Zero tile bounds from `Data/Tiles/ground_zero_tiles.json`.
+- Converts the 1 km UTM tile bounds to latitude/longitude.
+- Queries the USGS TNMAccess API for `Digital Elevation Model (DEM) 1 meter`
+  products in GeoTIFF format.
+- Stores the full TNM query response and selected product record.
+- Downloads the selected GeoTIFF source.
+- Updates the tile registry source record.
+
+## Selected Product
+
+```text
+title: USGS 1 Meter 10 x54y416 CA_CaliforniaGaps_B23
+dataset: Digital Elevation Model (DEM) 1 meter
+format: GeoTIFF
+publication_date: 2025-08-20
+source: USGS TNMAccess / ScienceBase / 3DEP
+```
+
+The product is a 10 km x 10 km 1-meter DEM tile that covers the 1 km Ground Zero
+MVP tile.
+
+## Local Files
+
+```text
+Data/Terrain/Sources/gz_us_ca_pacifica_utm10n_e544_n4160/
+```
+
+Expected files:
+
+- `gz_us_ca_pacifica_utm10n_e544_n4160_tnm_1m_dem_product.json`
+- `USGS_1M_10_x54y416_CA_CaliforniaGaps_B23.tif`
+- `USGS_1M_10_x54y417_CA_CaliforniaGaps_B23.tif`
+
+Ground Zero sits on a 3DEP 10 km tile boundary, so both source GeoTIFFs are
+needed to extract the full 1 km MVP tile.
+
+## Subset Extraction
+
+```text
+Scripts/extract_ground_zero_dem_subset.py
+```
+
+This script extracts the exact 1 km Ground Zero subset from the source GeoTIFFs.
+It requires `rasterio` or equivalent GDAL Python support.
+
+The extraction output is:
+
+```text
+Data/Terrain/Extracted/gz_us_ca_pacifica_utm10n_e544_n4160/
+```
+
+Generated files:
+
+- `gz_us_ca_pacifica_utm10n_e544_n4160_1m_dem_subset.tif`
+- `gz_us_ca_pacifica_utm10n_e544_n4160_1m_dem_subset_metadata.json`
+
+Current extracted subset:
+
+```text
+size: 1000 x 1000 pixels
+pixel_size: 1 m x 1 m
+crs: EPSG:26910 / NAD83 UTM zone 10N
+bounds: E 544000-545000, N 4160000-4161000
+```
+
+## Notes
+
+- The USGS product is the final MVP target elevation source.
+- The older USGS EPQS 33 x 33 heightmap remains useful as a fast prototype and
+  sanity check, but the 1-meter GeoTIFF is the source we should use for the real
+  Unreal terrain tile.
+- The selected products are larger than the 1 km MVP tile; this is expected for
+  3DEP 1-meter DEM products.