Edit values for total station¶
Use this dialog to enter calibration data for total station (theodolite and distance meter) and assumed standard deviation for observed directions, distances, and zenith distances. This information is used for correction of measured distances and weighting of observations, respectively.
Where do I find the dialog?¶
On the toolbar in the terrain modeling drawing, select the icon for Gemini Terrain Settings... and then Surveying: Instruments under Common settings.
Number¶
Internal numbering system for the instrument.
If you need to enter the total station number using the Replace function in the list window, use the notation 1/1, 1/2, ..., 1/9.
Name¶
Designation of the instrument combination.
Standard deviation¶
Assumed observation accuracy when using the instrument combination. It distinguishes between the different observation types: direction measurement, zenith distance, and distance measurement.
Each observation's standard deviation is divided into three parts:
- Constant part: Distance-independent standard deviation. Expressed in gon or meters.
- Distance-dependent part: Distance-dependent standard deviation. Expressed in meters/km or gon/km.
- Centering: Assumed centering accuracy in meters.
Calibration¶
Addition constant: Specified in meters. Added to measured distance. (Any prism constant for the instrument combination must be added to the addition constant from the calibration.)
Scale: Delta value for scale correction (ppm = mm/km). Positive scale factor gives a positive addition to measured distance.
Reference pressure: Comparison pressure for calibration data.
When talking about comparison pressure during calibration of total stations, it means in practice:
- You define a reference pressure (often standard atmosphere: approx. 1013.25 hPa).
- At this pressure, you know what the instrument should measure (either through a known measurement or factory-set values).
- Then you compare the instrument's actual measurement with the expected result at this reference pressure.
This reveals any deviation. The deviation is what you adjust for during calibration, so that the instrument gives correct values also under other pressure conditions.
You must select pressure unit for the instrument: Auto, mmHg, or hPa and enter reference pressure.
In previous versions of the program, we only had automatic selection of pressure unit. The pressure unit, mmHg or hPa, was derived from the value in the field. This will still happen if you select method Auto. The intervals used are 300 ≤ mmHg ≤ 780, 780 < hPa ≤ 1100.
Warning
Auto can work poorly in some contexts, for example for underwater tunnels where the pressure is very low.
Note
mmHg and hPa have the same zero point, and for conversion you can use: 760 mmHg = 1013.25 hPa, which gives the formula for conversion: hPa = mmHg × 1.33322.
Reference temp: Comparison temperature for calibration data (Celsius).
Total standard deviation (Std)¶
Std² = (StdC + D*StdA)² + (StdS)² for distance.
Std² = (StdC + D*StdA)² + (StdS/D)² for direction.
Std² = StdC² + (D*StdA)² + (StdS/D)² for zenith distance.
Where StdC and StdA are the observation's constant and distance-variable parts respectively, StdS is centering accuracy, and D is distance. It is this total standard deviation that is eventually transferred to the observation (if you have not entered other values there yourself or request to update standard deviation).
Note
If you want to use the formulas to calculate the standard deviation for a given observation, you must pay attention to the units.
Alt.1: gon is converted to radians (PI/200) before you enter the numbers into the formula, i.e., the parameters for constant part and distance-dependent part. At the very end, the final answer is converted back from radians to gon (200/PI).
Alt.2: The centering part (StdS/D) is converted to gon (200/PI). Then all terms will have unit gon. This will give the same answer as alt.1.
Values for calculating standard deviation
| Observation type | Constant part | Distance-dependent part | Centering |
|---|---|---|---|
| Direction measurement | 0.0005 gon | 0.0000 gon/km | 0.003 m |
| Zenith distance | 0.0005 gon | 0.0025 gon/km | 0.003 m |
| Distance measurement | 0.003 m | 0.002 m/km | 0.003 m |