For example, you have

point 1: x1, y1

point 2: x2, y2

point 3: x3, y3

and point 0: z0

I suggest the following:

point 1: x1, y1, z0 -> set accuracy 1/100

point 2: x2, y2, z0 -> set accuracy 1/100

point 3: x3, y3, z0 -> set accuracy 1/100

point 0: x, y, z0 -> set accuracy 1000/1

where x and y are somewhere close to the first three points.