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⚡️ Speed up method GlobalMercator.LatLonToMeters by 26% #12

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⚡️ Speed up method GlobalMercator.LatLonToMeters by 26% #12

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40 changes: 30 additions & 10 deletions opendm/tiles/gdal2tiles.py
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,20 @@
from osgeo import gdal
from osgeo import osr

_PI = math.pi

_ORIGIN_SHIFT = 2 * _PI * 6378137 / 2.0

_DEG2RAD = _PI / 180.0

_RAD2DEG = 180.0 / _PI

_INV_180 = 1.0 / 180.0

_LOG = math.log

_TAN = math.tan

try:
from PIL import Image
import numpy
Expand Down Expand Up @@ -204,20 +218,26 @@ 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
self.initialResolution = 2 * _PI * 6378137 / self.tileSize
# 156543.03392804062 for tileSize 256 pixels
self.originShift = 2 * math.pi * 6378137 / 2.0
# 20037508.342789244
self.originShift = _ORIGIN_SHIFT

def LatLonToMeters(self, lat, lon):
"Converts given lat/lon in WGS84 Datum to XY in Spherical Mercator EPSG:3857"

mx = lon * self.originShift / 180.0
my = math.log(math.tan((90 + lat) * math.pi / 360.0)) / (math.pi / 180.0)

my = my * self.originShift / 180.0
"""Converts given lat/lon in WGS84 Datum to XY in Spherical Mercator EPSG:3857"""
# Inline arithmetic and use constant multipliers to optimize math expressions

# Avoid attribute lookups, use module-level constants
mx = lon * _ORIGIN_SHIFT * _INV_180
# The expression (90 + lat) * math.pi / 360 converts to radians for the mercator projection
# Avoid redundant math calls and variables
# Compute (90 + lat) * _DEG2RAD / 2
lat_rad = (90.0 + lat) * (_DEG2RAD * 0.5)
tan_lat = _TAN(lat_rad)
log_tan_lat = _LOG(tan_lat)
my = log_tan_lat * _RAD2DEG
my = my * _ORIGIN_SHIFT * _INV_180
return mx, my

def MetersToLatLon(self, mx, my):
Expand Down