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Geo Processing Tools — Cortex

Overview

DEM processing, vector tile generation, and PMTiles manipulation tools installed on cortex for compute-tier geospatial batch jobs. Cortex is compute-only — no persistent operational data lives here. Data flows: pi-nas (archive) → cortex (compute) → pi-nas + VM 1130 (outputs).

Installed Tools

Tool	Version	Package	Purpose
gdal_contour	GDAL 3.8.4	gdal-bin (apt)	Generate contour lines from DEM rasters
gdalinfo	GDAL 3.8.4	gdal-bin (apt)	Raster metadata inspection
gdal_translate	GDAL 3.8.4	gdal-bin (apt)	Raster format conversion
gdalbuildvrt	GDAL 3.8.4	gdal-bin (apt)	Virtual raster mosaics
ogr2ogr	GDAL 3.8.4	gdal-bin (apt)	Vector format conversion
tippecanoe	v2.49.0	tippecanoe (apt)	GeoJSON → vector tiles (MBTiles/PMTiles)
pmtiles	v1.30.2	go-pmtiles (binary)	PMTiles inspection, conversion, tile extraction

Installed: 2026-04-22

Ephemeral Scratch Convention

All temporary/staging data goes in /home/zvx/scratch/. This directory is cleaned after batch jobs complete. Never treat scratch as persistent storage.

Typical layout:

/home/zvx/scratch/
└── nav-processing/          # Current: staged DEM for contour generation
    └── hillshade-na.pmtiles # 93 GB terrarium DEM (from pi-nas archive)

Terrarium DEM Decode

The Mapzen Terrarium format encodes elevation in RGB PNG tiles:

elevation_meters = (R * 256 + G + B/256) - 32768

To use with GDAL: decode RGB → Float32 elevation array → write as GeoTIFF via VRT with subClass="VRTRawRasterBand".

Data Tier Architecture

Tier	Host	Role	Example
Archive	pi-nas (192.168.1.245)	Source of truth, recovery	`/export/data/nav/hillshade-na.pmtiles`
Compute	cortex (192.168.1.150)	Batch processing, scratch	`/home/zvx/scratch/nav-processing/`
Operational	VM 1130 (192.168.1.130)	Serving tiles via nginx	`/mnt/nav/tiles/`

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