Policy Walkthrough

This guide walks through two real-world Fusion Policies: a simple regional overlay and a complex multi-tier coastal model.

1. Simple Fusion: Great Barrier Reef

Goal: Enhance the global GEBCO bathymetry with high-resolution (100m) local survey data for the Great Barrier Reef (GBR100).

Key Concepts: * Base Layer: GEBCO 2025 (~450m resolution). * Overlay: GBR100 (~100m resolution). * Metric Feathering: Blending the edges over 500m to hide the seam.

name: "Great Barrier Reef Fusion"
crs: "EPSG:4326"

variables:
  - name: "elevation"
    steps:
      # 1. Base Layer (Global)
      - provider: "gebco_2025"
        operator: "overwrite"

      # 2. Local Overlay (Feathered)
      - provider: "jcu_gbr100"
        operator: "metric_feather"
        blend_distance: 500.0

Outcome: The output is a seamless grid where GBR100 data dominates usage, but smoothly transitions to GEBCO in deep water or at the edge of the survey.

2. Complex Fusion: US Coastal (WLIS)

Goal: Create a “Digital Twin” quality model for Western Long Island Sound (WLIS) using every available dataset priority.

Key Concepts: * Priority Overwrite: Using a strict hierarchy where better data strictly replaces worse data. * 7-Layer Stack: Handling Terrestrial, Intertidal, and Bathymetric zones securely. * Global Projection: Using EPSG:3857 (Web Mercator) for compatibility with web viewers.

The Stack (Bottom-Up):

  1. Global Base: GEBCO 2025 (Ensures no void pixels).

  2. Regional Land: USGS 3DEP (10m) for upland context.

  3. Regional Bathy: NOAA CUDEM (3m) gap-filling coastal zones.

  4. Modern Bathy: NOAA BlueTopo (2-8m) high-quality modeled bathymetry.

  5. Shallow Water: Topobathy Lidar (Green Laser) for the intertidal zone.

  6. Upland Detail: USGS 3DEP Lidar (Airborne) for structures and coastline.

  7. Survey Truth: NOAA BAGs (Multibeam) for precise channel depth.

name: "US Coastal Topobathy Fusion"
crs: "EPSG:3857"

variables:
  - name: "elevation"
    steps:
      # --- Base Layers ---
      - provider: "gebco_2025"
        operator: "overwrite"

      - provider: "usgs_3dep"
        product: "10m"
        operator: "overwrite"

      # --- Middle Tiers ---
      - provider: "ncei_cudem"
        operator: "overwrite"

      - provider: "noaa_bluetopo"
        operator: "overwrite"

      # --- High Res Lidar ---
      - provider: "noaa_topobathy"
        operator: "overwrite"

      - provider: "usgs_lidar"
        operator: "overwrite"

      # --- Survey Truth (Top Priority) ---
      - provider: "ncei_bag"
        operator: "overwrite"

Outcome: A high-fidelity model that is “Best Available” at every pixel. If a ship survey (BAG) exists, it is used. If not, Lidar is used. If that fails, BlueTopo/CUDEM are used. Finally, GEBCO fills the deep ocean.