utils.py 文件源码

def get_tolerance(zoom_level):

    # pixels squared factor
    tolerance_square_pixels = 7

    # default Google/Bing map tile scales
    metres_per_pixel = 156543.03390625 / math.pow(2.0, float(zoom_level + 1))

    # the tolerance (metres) for vector simplification using the VW algorithm
    square_metres_per_pixel = math.pow(metres_per_pixel, 2.0)

    # tolerance to use
    tolerance = square_metres_per_pixel * tolerance_square_pixels

    return tolerance


# maximum number of decimal places for boundary coordinates - improves display performance