topology_exception.py

# -*- coding: utf-8 -*-
"""
Created on Sat Dec 31 12:22:50 2016

@author: ironbar

Function for dealing with topology exception errors
"""
import pandas as pd
import numpy as np
import time
import shapely
import shapely.geometry



def __get_valid_wkt_str(input, precision, debug_print):
    """
    Function that checks that a wkt str is valid
    """
    if type(input) is str:
        wkt_str = input
    else:
        #Get the initial str
        wkt_str = shapely.wkt.dumps(input, rounding_precision=precision)
    #Loop until we find a valid polygon
    for i in range(100):
        polygon = shapely.wkt.loads(wkt_str)
        if not polygon.is_valid:
            #print debugging info
            print 'Invalid polygon in %s. Iteration: %i' % (debug_print, i)
            #Use buffer to try to fix the polygon
            polygon = polygon.buffer(0)
            #Get back to multipolygon if necesary
            if polygon.type == 'Polygon':
                polygon = shapely.geometry.MultiPolygon([polygon])
            #Dump to str again
            wkt_str = shapely.wkt.dumps(polygon, rounding_precision=precision)
        else:
            break
    return wkt_str

    
def __create_square_around_point(point, side):
    """
    Creates a square polygon with shapely given 
    the center point
    """
    #Create canonical square points
    square_points = np.zeros((4,2))
    square_points[1, 0] = 1
    square_points[2] = 1
    square_points[3, 1] = 1
    #Scale the square
    square_points *= side
    #Position to have the point in the center
    for i in range(2):
        square_points[:, i] += point[i] - side/2.
    pol = shapely.geometry.Polygon(square_points)
    return pol    
    
def repair_topology_exception(submission_path, precision, image_id, n_class, point, 
                              side=1e-4):
    """
    Tries to repair the topology exception error by creating a squared 
    hole in the given point with the given side
    """
    start_time = time.time()
    #Load the submission
    print 'Loading the submission...'
    df = pd.read_csv(submission_path)
    #Loop over the values changing them
    #I'm going to use the values because I think iterating over the dataframe is slow
    #But I'm not sure
    print 'Looping over the polygons'
    polygons = df.MultipolygonWKT.values
    img_ids = df.ImageId.values
    class_types = df.ClassType.values
    for i, polygon, img_id, class_type in zip(range(len(polygons)), polygons,
                                           img_ids, class_types):
        if img_id == image_id and n_class == class_type:
            polygon = shapely.wkt.loads(polygon)
            square = __create_square_around_point(point, side)
            polygon = polygon.difference(square)
            polygons[i] = __get_valid_wkt_str(polygon, precision,
                '%s class%i' % (img_id, class_type))
    #Update the dataframe
    df.MultipolygonWKT = polygons
    #Save to a new file
    print 'Saving the submission...'
    df.to_csv(submission_path,
              index=False)
    print 'It took %i seconds to repair the submission' % (
        time.time() - start_time)

if __name__ == '__main__':
    repair_topology_exception('/home/guillermo/sample_submission.csv', 
                              precision=6, 
                              image_id='6100_0_2', 
                              n_class=4, 
                              point= (0.006539, -0.005582), 
                              side=1e-4)