run2-antimeridian-handling - SKILL.md Agent Skill

name: run2_antimeridian-handling description: Handling the antimeridian (180/-180 longitude) in geospatial analysis with GeoPandas and Shapely.

Antimeridian Handling in GeoPandas

The Problem

The Pacific plate spans the antimeridian (International Date Line at 180/-180 degrees longitude). Standard operations in EPSG:4326 may split geometries incorrectly.

PB2002 Dataset Behavior

The PB2002 plate polygons in GeoJSON handle the antimeridian by having bounds from -180 to 180.
The Pacific plate polygon's bounds are (-180, -66, 180, 60), meaning it wraps correctly.
gpd.sjoin(predicate="within") works correctly with these polygons for point-in-polygon tests.

Projection Solution

When computing distances, project to a CRS centered in the Pacific:

# Center at 160°W (middle of Pacific Ocean)
crs = "+proj=aeqd +lat_0=0 +lon_0=-160 +datum=WGS84 +units=m"

This avoids antimeridian splitting because the projection center is far from the antimeridian.

Alternative: Shift Longitudes

# Shift all longitudes to [0, 360] range
def shift_lon(geom):
    from shapely.affinity import translate
    # This is complex for polygons; projection is simpler
    pass

Projection is generally the better approach.