Finding best-fit zoom level given a shapely geometry

endpoint.geojson

find_best_zoom.py

import json
import math

from shapely.geometry import shape, MultiPoint


def find_zoom(geom, paddingFactor): 

    # translated from C# code here: https://gis.stackexchange.com/a/19652/
    minX, minY, maxX, maxY = geom.bounds

    ry1 = math.log((math.sin(deg2rad(minY)) + 1) / math.cos(deg2rad(minY)))
    ry2 = math.log((math.sin(deg2rad(maxY)) + 1) / math.cos(deg2rad(maxY)))

    ryc = (ry1 + ry2) / 2
    centerY = rad2deg(math.atan(math.sinh(ryc)))

    resolutionHorizontal = abs(minX - maxX) / 500.

    vy0 = math.log(math.tan(math.pi*(0.25 + centerY / 360)))
    vy1 = math.log(math.tan(math.pi*(0.25 + maxX/360)))
    viewHeightHalf = 300. / 2.
    zoomFactorPowered = viewHeightHalf / (40.7436654315252*(vy1 - vy0))

    resolutionVertical = 360.0 / (zoomFactorPowered * 256)

    resolution = max(resolutionHorizontal, resolutionVertical) * paddingFactor
    zoom = math.log(360 / (resolution * 256), 2)

    return zoom


def deg2rad(degree):
    return degree*(math.pi/180)


def rad2deg(rad):
    return (rad*180) / math.pi


if __name__ == '__main__':
    with open('startpoint.geojson') as src:
        start_pt = shape(json.load(src)['geometry'])

    with open('endpoint.geojson') as src:
        end_pt = shape(json.load(src)['geometry'])

    multi_point = MultiPoint([start_pt, end_pt])
    paddingFactor = 1

    zoom = find_zoom(multi_point, paddingFactor)

    print(zoom)
    print(multi_point.centroid.coords[0])

startpoint.geojson