A new Excel tool has been added – the xls4Oracle Google Earth Area.
With the Excel tool you can copy / paste the polygon kml data from Google Earth into Excel. A macro will calculate the area and insert a line into the sheet, with area, perimeter and latitude/longitude of the polygon.
About the Area calculation
The Area calculation is done by summarizing all triangles, defined by the starting point and two following points. As long as bearing from last point is higher than previous point triangle area is added. If bearing of the last point is less than the previous point, the triangle area is subtracted.
In the figure below, the starting point is the lower left corner. The first two triangels are positive, the third is negative (because of the counterclockwise bearing change) and the fourth is positive. The tricky triangles are number 2, 3 and 4 – number 2 and 3 include area outside the polygon, but that area is eliminated when triangle number 3 is subtracted. You get the same result by counting the squares. The same rule applies for spheric surfaces like the earth. Triangle sides is calculated as great circle distances.