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⚡️ Speed up method GlobalMercator.TileLatLonBounds by 45% #18

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⚡️ Speed up method GlobalMercator.TileLatLonBounds by 45% #18

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33 changes: 19 additions & 14 deletions opendm/tiles/gdal2tiles.py
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Original file line number Diff line number Diff line change
Expand Up @@ -209,7 +209,10 @@ def __init__(self, tileSize=256):
self.initialResolution = 2 * math.pi * 6378137 / self.tileSize
# 156543.03392804062 for tileSize 256 pixels
self.originShift = 2 * math.pi * 6378137 / 2.0
# 20037508.342789244
self._inv_originShift = 180.0 / self.originShift
self._pi = math.pi
self._deg_per_rad = 180.0 / self._pi
self._pi_per_2 = self._pi / 2.0

def LatLonToMeters(self, lat, lon):
"Converts given lat/lon in WGS84 Datum to XY in Spherical Mercator EPSG:3857"
Expand All @@ -221,12 +224,11 @@ 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"

lon = (mx / self.originShift) * 180.0
lat = (my / self.originShift) * 180.0

lat = 180 / math.pi * (2 * math.atan(math.exp(lat * math.pi / 180.0)) - math.pi / 2.0)
"""Converts XY point from Spherical Mercator EPSG:3857 to lat/lon in WGS84 Datum"""
# Use precomputed values for speedup
lon = mx * self._inv_originShift
lat = my * self._inv_originShift
lat = self._deg_per_rad * (2.0 * math.atan(math.exp(lat * self._pi / 180.0)) - self._pi_per_2)
return lat, lon

def PixelsToMeters(self, px, py, zoom):
Expand Down Expand Up @@ -265,19 +267,22 @@ def MetersToTile(self, mx, my, zoom):
return self.PixelsToTile(px, py)

def TileBounds(self, tx, ty, zoom):
"Returns bounds of the given tile in EPSG:3857 coordinates"

minx, miny = self.PixelsToMeters(tx*self.tileSize, ty*self.tileSize, zoom)
maxx, maxy = self.PixelsToMeters((tx+1)*self.tileSize, (ty+1)*self.tileSize, zoom)
"""Returns bounds of the given tile in EPSG:3857 coordinates"""
# Reduce multiplications by saving tile size
ts = self.tileSize
# Inline PixelToMeters math for two calls, saves call overhead and speeds up computation
res = self.initialResolution / (2 ** zoom)
minx = tx * ts * res - self.originShift
miny = ty * ts * res - self.originShift
maxx = (tx + 1) * ts * res - self.originShift
maxy = (ty + 1) * ts * res - self.originShift
return (minx, miny, maxx, maxy)

def TileLatLonBounds(self, tx, ty, zoom):
"Returns bounds of the given tile in latitude/longitude using WGS84 datum"

"""Returns bounds of the given tile in latitude/longitude using WGS84 datum"""
bounds = self.TileBounds(tx, ty, zoom)
minLat, minLon = self.MetersToLatLon(bounds[0], bounds[1])
maxLat, maxLon = self.MetersToLatLon(bounds[2], bounds[3])

return (minLat, minLon, maxLat, maxLon)

def Resolution(self, zoom):
Expand Down