Feature Request: Add "Point on Surface" Extraction Method for Polygons

[fuadyassin]

The current extract_centroid method works well for most polygons but may return points outside the boundary. Adding a method to extract the point on surface using GeoPandas' representative_point() would make sure the point lies within the polygon.

Proposed Functionality to be added in the utility and for drainage database lat long coordinates:

def extract_point_on_surface(gdf, obj_id, epsg=4326):
    if not gdf.crs:
        gdf.set_crs(epsg=4326)
    point_on_surface = gdf.geometry.representative_point()
    if gdf.crs.to_epsg() != epsg:
        point_on_surface = gdf.to_crs(epsg=epsg).geometry.representative_point()
    coords_df = pd.DataFrame({
        obj_id: gdf[obj_id],
        'lat': point_on_surface.y,
        'lon': point_on_surface.x
    })
    return coords_df

This will make sures extracted points always lie within the polygon boundary.
Provides users an alternative to centroid-based coordinates.
This would be a great addition to complement the existing functionality.

[kasra-keshavarz]

Thanks Fuad, I'll merge this into the main branch soon.

[mee067]

we need to enhance this for gauge locations as we talked before. Gauges at the outlets are not always mapped to the correct subbasin as the centroid of another subbasin maybe closer to the gauge. Can we supply polygon outlets (intersection of river and subbasin shape) instead of centroids?

[fuadyassin]

@mee067 Thank you for pointing that out. The enhancement to flag stations or use polygon outlets (intersection of river and subbasin shape) is indeed another development we are working on. For now, this update ensures that the centroid is correctly placed within the polygon and improves the default streamflow station identification function. The additional improvement you mentioned will be implemented as an alternative option alongside the default method in future updates.