In the figure, we can obtain n-2 triangles in all. The area of each triangle can be obtained by the exterior product of the two plane vectors composed by the three vertexes. For example,area of is.
Because of the operation of vector exterior product each dependent small triangle has division of positive and negative.
In practical farmland area measurement, the start point GPS receiver obtained is usually used as coordinate origin. Then the plane right-angle coordinates showed as figure 1 along latitude and longitude direction is built. After a new point received, the MCU calculate the long and latitude of the point, and then use formula 1 and 2 to calculate the coordinate of the point relative to origin. Calculate area and make algebraic sum accumulation by substitution of the coordinate into formula 3 . Then the area of the farmland can be obtained by formula 3 after receiver received all plots of the farmland range.