Fusion Policy DSL

TopoBathySim logic is defined in Fusion Policy files (YAML). A policy describes what data to fetch and how to combine it to create a variable (e.g., elevation).

Structure

A policy file consists of metadata and a list of variables (layers) to generate.

name: "Western Long Island Sound Fusion"
version: "1.1.0"
crs: "EPSG:3857"  # Output Coordinate Reference System

variables:
  - name: "elevation"
    description: "Topobathymetry (Meters)"
    steps:
      # List of composition steps (Bottom-Up order)
      - provider: "gebco"
        product: "sub_ice_topo_bathymetry"
        operator: "overwrite"

      - provider: "usgs_3dep"
        product: "1m"
        operator: "overwrite"

Variables

Currently, the runtime supports generating a single variable: elevation. Future versions may support uncertainty or source masks.

Composition Steps

The steps list defines the fusion order. Steps are processed sequentially. Later steps are applied on top of previous steps using the specified Operator.

Fields

provider: The registered provider alias (e.g., gebco, usgs_3dep, ncei_bag).
product: (Optional) Product sub-type passed to the provider.
operator: The blending operation to apply.
description: (Optional) Human-readable note.
transitions: (Optional) A list of rules for smoothing edges based on what lies beneath.

Operators

overwrite

Hard replacement. Where the new layer has data (valid), it replaces the underlying value.

operator: "overwrite"

metric_feather

Smooths the transition between the new layer and the base layer over a specified distance.

operator: "metric_feather"
blend_distance: 100.0  # Meters

Topologies (Transition Rules)

For advanced fusion, you can specify Transition Rules to apply different operators depending on which provider is currently at a pixel in the base layer.

Example: Feather into GEBCO (Bathymetry), but Hard-Cut against USGS Lidar (Land).

- provider: "noaa_bluetopo"
  operator: "overwrite"  # Default
  transitions:
    - target_provider: "gebco"
      operator: "metric_feather"
      blend_distance: 500.0