AgrarianGameArchive/Docs/Terrain/DemAcquisition.md

Ground Zero DEM Acquisition

Purpose

This document records the official USGS 3DEP DEM product selected for the Ground Zero MVP tile.

Acquisition Script

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

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

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

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:

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:

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.