Calculates the surface area of a triangle based on a set of XYZCoords.

`sa_triangle(XYZcoords)`

- XYZcoords
A data frame with XYZ coordinates of three points in following order: X1,X2,X3,Y1,Y2,Y3,Z1,Z2,Z3.

The surface area of the triangle.

```
sa_triangle(c(X1 = 1, X2 = 2, X3 = 3 , Y1 = 1, Y2 = 2, Y3 = 1, Z1 = 1, Z2 = 1, Z3 = 1))
#> Y2
#> 1
```