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⚡️ Speed up method GlobalMercator.MetersToLatLon by 27% #13

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⚡️ Speed up method GlobalMercator.MetersToLatLon by 27% #13

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24 changes: 18 additions & 6 deletions opendm/tiles/gdal2tiles.py
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,14 @@
from osgeo import gdal
from osgeo import osr

_INV_PI = 1.0 / math.pi

_HALF_PI = math.pi / 2.0

_RAD_TO_DEG = 180.0 / math.pi

_DEG_TO_RAD = math.pi / 180.0

try:
from PIL import Image
import numpy
Expand Down Expand Up @@ -204,12 +212,11 @@ class GlobalMercator(object):
"""

def __init__(self, tileSize=256):
"Initialize the TMS Global Mercator pyramid"
"""Initialize the TMS Global Mercator pyramid"""
self.tileSize = tileSize
self.initialResolution = 2 * math.pi * 6378137 / self.tileSize
# 156543.03392804062 for tileSize 256 pixels
self.originShift = 2 * math.pi * 6378137 / 2.0
# 20037508.342789244

def LatLonToMeters(self, lat, lon):
"Converts given lat/lon in WGS84 Datum to XY in Spherical Mercator EPSG:3857"
Expand All @@ -221,12 +228,17 @@ def LatLonToMeters(self, lat, lon):
return mx, my

def MetersToLatLon(self, mx, my):
"Converts XY point from Spherical Mercator EPSG:3857 to lat/lon in WGS84 Datum"
"""Converts XY point from Spherical Mercator EPSG:3857 to lat/lon in WGS84 Datum"""
# Avoid attribute lookups and minimize repeated computation

lon = (mx / self.originShift) * 180.0
lat = (my / self.originShift) * 180.0
originShift = self.originShift
lon = (mx / originShift) * 180.0
# Compute intermediate value for latitude
lat = (my / originShift) * 180.0

lat = 180 / math.pi * (2 * math.atan(math.exp(lat * math.pi / 180.0)) - math.pi / 2.0)
# Fast path: minimize attribute lookups and localize using constants
rad = lat * _DEG_TO_RAD
lat = _RAD_TO_DEG * (2.0 * math.atan(math.exp(rad)) - _HALF_PI)
return lat, lon

def PixelsToMeters(self, px, py, zoom):
Expand Down