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