QArea.mac

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!QArea.mac
!benguest@gmail.com
!DESCRIPTION: This macro calculates the quadrilateral
!  area formed by four points (x,y) on a plane.
!  See GreenPaper (CEV_080131)
!PRECONDITIONS:
!  Point 1: (x1,y1)=(ARG1,ARG2)
!  Point 2: (x2,y2)=(ARG3,ARG4)
!  Point 3: (x3,y3)=(ARG5,ARG6)
!  Point 4: (x4,y4)=(ARG7,ARG8)
!  -Points 1-4 must circumnavigate the quadrilateral
!  -No interior angle of the quadrilateral can be
!   greater than 180 degrees.
!POSTCONDITIONS:
!  Area4= parameter containing the area of the
!         quadrilateral
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!Assign Points
x1=Arg1  !point 1
y1=Arg2

x2=Arg3  !point 2
y2=Arg4

x3=Arg5  !point 3
y3=Arg6

x4=Arg7  !point 4
y4=Arg8

L1=sqrt((x2-x1)**2+(y2-y1)**2) !Calculate Distances
L2=sqrt((x3-x2)**2+(y3-y2)**2)
L3=sqrt((x4-x3)**2+(y4-y3)**2)
L4=sqrt((x1-x4)**2+(y1-y4)**2)
b=sqrt((x4-x2)**2+(y4-y2)**2)

!Law of Cosines
T1=ACOS((L4**2+b**2-L1**2)/(2*L4*b))
T2=ACOS((L2**2+b**2-L3**2)/(2*L2*b))

h1=L4*sin(T1) !Calculate triangle heights
h2=L2*sin(T2)

!RETURN AREA
Area4=(1/2)*b*(h1+h2)
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!ITS THE END OF THE MACRO AS WE KNOW IT AND I FEEL FINE