@Matthew_Brown

Unless you can’t ensure that the points are taken in strict order/direction (*i.e. clockwise or counter-clockwise direction*), you won’t be able to get an accurate calculation even with a 3rd party service. Provided you can maintain that data collection order, than it’s a very easy match calculation to do even without using a 3rd party service.

Assume 4 points as [PT1] to [PT4] and points taken in clockwise direction:

**SQ FT CALCULATION**

```
IFS(
DISTANCE([PT2],[PT1]) = DISTANCE([PT4],[PT3]),
IFS(
DISTANCE([PT3],[PT2]) < DISTANCE([PT4],[PT1]),
((DISTANCE([PT2],[PT1]) * DISTANCE([PT3],[PT2])) + (DISTANCE([PT2],[PT1]) * (DISTANCE([PT4],[PT1]) - DISTANCE([PT3],[PT2]))) / 2) * 10763910.0000,
DISTANCE([PT3],[PT2]) > DISTANCE([PT4],[PT1]),
((DISTANCE([PT2],[PT1]) * DISTANCE([PT3],[PT2])) + (DISTANCE([PT2],[PT1]) * (DISTANCE([PT3],[PT2]) - DISTANCE([PT4],[PT1]))) / 2) * 10763910.0000,
TRUE,
DISTANCE([PT2],[PT1]) * DISTANCE([PT3],[PT2]) * 10763910.0000
),
DISTANCE([PT2],[PT1]) > DISTANCE([PT4],[PT3]),
((DISTANCE([PT4],[PT3]) * DISTANCE([PT3],[PT2])) + (DISTANCE([PT3],[PT2]) * (DISTANCE([PT2],[PT1]) - DISTANCE([PT4],[PT3]))) / 2) * 10763910.0000,
TRUE,
((DISTANCE([PT2],[PT1]) * DISTANCE([PT3],[PT2])) + (DISTANCE([PT3],[PT2]) * (DISTANCE([PT4],[PT3]) - DISTANCE([PT2],[PT1]))) / 2) * 10763910.0000
)
```

**ACRES CALCULATION**

```
IFS(
DISTANCE([PT2],[PT1]) = DISTANCE([PT4],[PT3]),
IFS(
DISTANCE([PT3],[PT2]) < DISTANCE([PT4],[PT1]),
((DISTANCE([PT2],[PT1]) * DISTANCE([PT3],[PT2])) + (DISTANCE([PT2],[PT1]) * (DISTANCE([PT4],[PT1]) - DISTANCE([PT3],[PT2]))) / 2) * 247.1054,
DISTANCE([PT3],[PT2]) > DISTANCE([PT4],[PT1]),
((DISTANCE([PT2],[PT1]) * DISTANCE([PT3],[PT2])) + (DISTANCE([PT2],[PT1]) * (DISTANCE([PT3],[PT2]) - DISTANCE([PT4],[PT1]))) / 2) * 247.1054,
TRUE,
DISTANCE([PT2],[PT1]) * DISTANCE([PT3],[PT2]) * 247.1054
),
DISTANCE([PT2],[PT1]) > DISTANCE([PT4],[PT3]),
((DISTANCE([PT4],[PT3]) * DISTANCE([PT3],[PT2])) + (DISTANCE([PT3],[PT2]) * (DISTANCE([PT2],[PT1]) - DISTANCE([PT4],[PT3]))) / 2) * 247.1054,
TRUE,
((DISTANCE([PT2],[PT1]) * DISTANCE([PT3],[PT2])) + (DISTANCE([PT3],[PT2]) * (DISTANCE([PT4],[PT3]) - DISTANCE([PT2],[PT1]))) / 2) * 247.1054
)
```

Of course this approach disregards the area to be a parallelogram shape rather than a perfect rectangle. However, if you consider **Martin’s Law of Skewness**, the area of a parallelogram (*a rectangle which is shewed with an angle of alpha*), the area can be interpreted as:

and **provided the Skewness angle of the both opposite sides are equal than the area of that parallelogram is same than the perfect rectangle as the trigonometric limit approaches to 1**

The latter case; provided the Skewness angle of the opposite sides are not equal than (*which we call Obstructed Polygon*) you will need an Eigen Vector to correct the vector calculation of the so called area, which will need a GPS Total Station and I’m afraid in this case even a 3rd party service can’t help you for that calculation.

**Far more important, may be remind you that, the precision/accuracy of any GPS calculation strongly relies on the accuracy of the GPS accelerometer of the mobile device where it should be perfectly and appropriately calibrated.**