Gangmax Blog

GPS Shift

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# From: https://github.com/scateu/PyWGS84ToGCJ02
# Issue description: https://en.wikipedia.org/wiki/Restrictions_on_geographic_data_in_China

from math import pi,sqrt,sin,cos

# a python binding of https://on4wp7.codeplex.com/SourceControl/changeset/view/21483#353936

# Krasovsky 1940
#
# a = 6378245.0, 1/f = 298.3
# b = a * (1 - f)
# ee = (a^2 - b^2) / a^2
a = 6378245.0
ee = 0.00669342162296594323

# Shift "World Geodetic System -> Mars Geodetic System".
def shift(wgLat, wgLon):
    """
    transform(latitude,longitude) , WGS84
    return (latitude,longitude) , GCJ02
    """
    if (outOfChina(wgLat, wgLon)):
        return wgLat, wgLon
    dLat = transformLat(wgLon - 105.0, wgLat - 35.0)
    dLon = transformLon(wgLon - 105.0, wgLat - 35.0)
    radLat = wgLat / 180.0 * pi
    magic = sin(radLat)
    magic = 1 - ee * magic * magic
    sqrtMagic = sqrt(magic)
    dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * pi)
    dLon = (dLon * 180.0) / (a / sqrtMagic * cos(radLat) * pi)
    mgLat = wgLat + dLat
    mgLon = wgLon + dLon
    return mgLat, mgLon

def outOfChina(lat, lon):
    if (lon < 72.004 or lon > 137.8347):
        return True
    if (lat < 0.8293 or lat > 55.8271):
        return True
    return False

def transformLat(x, y):
    ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * sqrt(abs(x))
    ret += (20.0 * sin(6.0 * x * pi) + 20.0 * sin(2.0 * x * pi)) * 2.0 / 3.0
    ret += (20.0 * sin(y * pi) + 40.0 * sin(y / 3.0 * pi)) * 2.0 / 3.0
    ret += (160.0 * sin(y / 12.0 * pi) + 320 * sin(y * pi / 30.0)) * 2.0 / 3.0
    return ret

def transformLon(x, y):
    ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * sqrt(abs(x))
    ret += (20.0 * sin(6.0 * x * pi) + 20.0 * sin(2.0 * x * pi)) * 2.0 / 3.0
    ret += (20.0 * sin(x * pi) + 40.0 * sin(x / 3.0 * pi)) * 2.0 / 3.0
    ret += (150.0 * sin(x / 12.0 * pi) + 300 * sin(x / 30.0 * pi)) * 2.0 / 3.0
    return ret

def unshift(mgLat, mgLon):
    '''
    Unshift "Mars Geodetic System -> World Geodetic System".
    From: https://blog.csdn.net/coolypf/article/details/8686588
    Shift the given mars coordinates again to get the delta amount, then
    subtract the delta from the mars coordinates to get the original GPS
    coordinates.
    '''
    lat2, lon2 = shift(mgLat, mgLon)
    latDelta = lat2 - mgLat
    lonDelta = lon2 - mgLon
    return mgLat - latDelta, mgLon - lonDelta

def ton(degree, minute, second):
    ''' Convert "degree/minute/second" coordinate value to single numerial. '''
    return degree + minute * 1.0 / 60 + second * 1.0 / 3600

lat, lon = shift(39.90768, 116.39101)
print('Shifted lat={}, lon={}'.format(lat, lon))
lat, lon = unshift(lat, lon)
print('Unhifted lat={}, lon={}'.format(lat, lon))

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