IMBIE Polygon Export¶

This page documents how to export combined + extended IMBIE basin polygons from the rasterized basin masks.

Recommended command¶

The recommended settings for a robust, simplified output are:

ismip7-antarctic-imbie-polygons \
  --simplify-tolerance-m 16e3 \
  --min-hole-area-m2 0 \
  --validate

These options:

simplify basin boundaries with a 16 km tolerance,
remove all extension holes before final topology repair,
validate that final exported basins are geometrically valid and do not contain unacceptable overlaps.

Inputs and outputs¶

Input prerequisites:

A valid working directory ([workdir] base_dir) with topography and ISMIP grid configuration in your config.
IMBIE2 shapefiles are downloaded automatically if missing.
Rasterized extended basin masks are generated automatically if missing.

Primary output:

imbie2/extended_basin_polygons.shp (plus .shx, .dbf, .prj)

Debug outputs¶

The command also supports debug exports for troubleshooting polygon topology:

--debug-raster-only-shapefile <PATH>
- Writes polygons built directly from rasterized extended basins without unioning with original IMBIE polygons.
--debug-raster-only-simplified-shapefile <PATH>
- Same as above, but includes simplification and hole-removal settings.

Example:

ismip7-antarctic-imbie-polygons \
  --simplify-tolerance-m 16e3 \
  --min-hole-area-m2 0 \
  --debug-raster-only-shapefile imbie2/raster_only_debug.shp \
  --debug-raster-only-simplified-shapefile imbie2/raster_only_simplified_debug.shp \
  --validate

Notes on topology behavior¶

The export pipeline enforces a shared-boundary partition for raster-derived extensions, then combines with exact original IMBIE polygons basin-by-basin:

Build repaired extension polygons from raster masks.
Subtract the union of all original IMBIE polygons from each extension basin.
Union each cleaned extension basin with the exact original basin polygon.

This preserves original IMBIE geometry while producing clean extended basins.