White Paper - SX12 Tracking and Target Separation 8
https://geospatial.trimble.com
8
Figure 10b. The light returning from a small prism does not fill the entire front lens of the instrument and gives a
smaller image on the detector.
To summarize, we can conclude that:
- The tracker, EDM and telecamera are all coaxial.
- Minimum prism separation depends on prism size and range. The images of two targets need to be
separate on the detector for the tracker to interpret them as two targets.
- The SX12 has good target separation capabilities: about 40 mm center-to-center at close distances,
and 85 mm at 100 m.
- At short range, the minimum separation will mainly be limited by the defocus, though a smaller prism
will allow for a smaller minimum prism separation.
- At long range, the minimum prism separation will be limited by the resolution of the tracker system
and will approach a constant angle.
- Prisms that are 25 mm in diameter or larger have the same center-to-center minimum prism
separation.
Minimum Prism Separation - Practical Measurements
Prism size 25 mm diameter or larger Prism size 12.5 mm diameter
Distance to Target
[m]
Minimum
Separation [mm]
Minimum
Separation [deg]
Minimum
Separation [mm]
Minimum
Separation [deg]
5 39 0.447 22 0.244
10 43 0.244 26 0.146
15 47 0.179 30 0.114
20 50 0.142 33 0.095
30 55 0.105 39 0.074
50 64 0.073 49 0.056
100 85 0.049 72 0.041
250 124 0.028 118 0.027
Figure 10. The table above shows the minimum separation where the instrument can still distinguish two prisms
as separate targets. Both distance and angle refers to the center-to-center distance or angle between the prisms.
