**2 or 3 back sights for**

**Free Station (resection)?**

Following examples are calculated with BestNetwork

**Free Station is also known as Resection. Get Location of the total station by measuring distance and angles to known points (back sights).**

**Free Station with 2 known points**

**(back sights)**:- 1 new point (station) with unknown coordinates are marked in red (point 3).

- Existing points with known coordinates are marked in green (points 1, 2).

- Station on point 3 with observations (orange lines) to point 2 and 3

**Free Station with 3 known points**

**(back sights)**:- 1 new point (station) with unknown coordinates are marked in red (point 3).

- Existing points with known coordinates are marked in green (points 1, 2 and 4).

- Station on point 3 with observations (orange lines) to point 2, 3 and 4

**Example**

**Free Station with**

**2 back sights**

**Accuracy (blue error ellipse in map):**

Standard deviation is 3.5 mm. (notice that standard deviation of known points is set to 5 mm)

**Reliability:**

The report shows that the coordinates of point number 3 are not reliable. A false observation from station or a false coordinate of the reference points can cause an infinite wrong position of point 3 (999999 = infinite)

**Example**

**Free Station with**

**3**

**back sights**

**Accuracy (blue error ellipse in map):**

Standard deviation is 3 mm. There is not a very big improvement of accuracy if you are using 3 known points to set up your station.

**Reliability (yellow lines):**

The report shows that the coordinates of point number 3 are now reliable. A false observation from station to point number 2 can cause an wrong position of point 3 of 4 cm.

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