def cross(A,B):
return A[0] * B[1] - A[1] * B[0]
def vectorMinus( a , b):
return ( (a[0] - b[0] )*1000,(a[1] - b[1] )*1000)
def getLTDis( A, B ):
lon1, lat1, lon2, lat2 = map(radians, [A[0], A[1], B[0], B[1]])
dlon = lon2 - lon1
dlat = lat2 - lat1
a = sin(dlat/2)**2 + cos(lat1) * cos(lat2) * sin(dlon/2)**2
c = 2 * asin(sqrt(a))
r = 6371.393
#print A,B
return c * r * 1000.0
def triangleAre(A,B,C):
x,y,z = getLTDis(A,B),getLTDis(B,C),getLTDis(C,A)
c = (x + y + z) /2
return sqrt((c)*(c-y)*(c-z)*(c-x))
def grahamScanArea(data):
data.sort(key=lambda x:(x[0],x[1]),reverse=False)
ans = [ 0 ] * (len(data)*2)
m = 0
for item in data:
top = len(item)
while( m > 1 and cross( vectorMinus(ans[ m -1 ] , ans [ m - 2 ]), vectorMinus( item , ans [ m - 2 ] )) <= 0 ) : m = m -1
ans[m] = item
m = m + 1
k = m
flag = True
data.reverse()
for item in data:
if flag :
flag = False
continue
while( m > k and cross( vectorMinus(ans[ m -1 ] , ans [ m - 2 ]), vectorMinus( item , ans [ m - 2 ] )) <= 0) : m = m - 1
ans [m] = item
m = m + 1
m = m -1
b = [ ans[i] for i in range(0, m)]
if len(b) < 3 : return 0
#if DEBUG : print b
return AREA(b)
def AREA(b):
ans = 0.0
for i in range(len(b)):
if i == 0 or i + 1 >= len(b) : continue
x , y = b[i] , b[i + 1]
ans += triangleAre( b[0] , x , y )
return ans
