Calculate area of closed loop

[milkypros]

Hi
Is there any way to calculate the area of a closed loop that is created by a set of (x,y) points?

 

[mikrom]

You mean probably the area of closed curve. But when it's not given analytically by a formula, but by a set of points, then this is not a curve, but a polygon.
There are several methods to calculate the area of polygons - google for it.

 

[GerritGroot]

Place a point in the middle of the closed loop and use the sum of the halfs of the vector products (outproducts)

(This also works for volumes. In the old days they had mechanical planimeters... ...worth a google as well)

 

[milkypros]

I wrote the program below and it works fine. But is there any way for the program to read (x,y) data from an EXCEL worksheet?

parameter(NMAX=50)
real*4 buffer(NMAX,NMAX)

s=0
npoints=13 !13 points
! init buffer x(i), y(i)
do i=1, npoints
buffer(1,1)= 3; buffer(1,2)=3
buffer(2,1)=12; buffer(2,2)=3
buffer(3,1)=12; buffer(3,2)=6
buffer(4,1)=11; buffer(4,2)=6
buffer(5,1)=11; buffer(5,2)=7
buffer(6,1)=15; buffer(6,2)=7
buffer(7,1)=15; buffer(7,2)=9
buffer(8,1)= 8; buffer(8,2)=9
buffer(9,1)= 8; buffer(9,2)=6
buffer(10,1)=4; buffer(10,2)=6
buffer(11,1)=4; buffer(11,2)=9
buffer(12,1)=3; buffer(12,2)=9
buffer(13,1)=3; buffer(13,2)=3
end do
!calculate internal surface
do i=1, npoints-1
s=s+(buffer(i,1)+buffer(i+1,1))*(buffer(i,2)-buffer(i+1,2))
end do
s=abs(s)/2
!print surface
print *,''
print *,' Surface is: ', s
print *,''
print *,''
END

 

[mikrom]

Hi milkypros,
Yes, you used the formula for polygon area (

http://local.wasp.uwa.edu.au/~pbourke/geometry/polyarea

)

You can save your Excel data to CSV-format, which is the text file and then you can read them as you read data from text files.

 

[milkypros]

Thanks microm