Free Station (Resection) with 2 or 3 back sights

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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