Codes for Manipulating Geometric Objects

Geometric Objects.md

Geometric Objects

a set of utility functions for manipulating shapely.geometry objects

Colab Notebook

geometry.py

# -*- encoding: utf-8 -*-

"""
Codes for Manipulating Geometric Objects

A geometric object can be anything that is defined by
`shapely.geometry` class or read from shapefile using
`geopandas`. This code can be used to manipulate
these files for better control and requirement.

@author  : Debmalya Pramanik
"""


from shapely.geometry import (
    Polygon,
    MultiPolygon
)


def flatten(geometry : MultiPolygon) -> MultiPolygon:
    """
    Flatten a Higher-Order Multi-Polygon to a Second Order Polygon
    
    A higher order `Polygon` or `MultiPloygon` is often represented with
    `Z` symbol when parsed with `geopandas`. This type of frame is also
    vulnerable to `shapely` reading file error. The functions aims to
    flatten any higher dimensional data to only its `xy` form be simply
    considering first two dimensional values. For example:
    
    .. math:
       MultiPolygon Z(((1, 2, 3), (4, 5, 6)), ((1, 2, 3), (4, 5, 6))) > MultiPolygon(((1, 2), (4, 5)), ((1, 2), (4, 5)))
       
    As explained, all higher order terms are simply neglected forcefully using `xyz[:2]`
    comprehensions.
    """
    
    flattened = []
    for pt in geometry:
        # consider all has `z`
        # TODO raise error/catch when not met
        # also, implemented only for `MultiPolygon`
        if pt.geom_type == "Polygon":
            polys = [xyz[:2] for xyz in list(pt.exterior.coords)]
            flattened.append(Polygon(polys))
        elif pt.geom_type == "MultiPolygon":
            inner_multi_poly = []
            for ap in pt:
                # loop through inner multi-poly
                # discard any higher dimensional values
                polys = [xyz[:2] for xyz in list(ap.exterior.coords)]
                inner_multi_poly.append(Polygon(polys))
            flattened.append(MultiPolygon(inner_multi_poly))
        else:
            raise ValueError(f"{pt.geom_type} is not yet implemented.")
        
    return MultiPolygon(flattened)