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Tilt Compensation

Tilt compensation allows very accurate positional reading of points on the ground without the need to maintain an absolutely vertical, completely level surveying pole. Tilt compensation is also handy for measuring points up against obstacles that interfere with a vertical pole.

Configuration​

By default, tilt compensation is enabled. See the Instrument configuration section to disable the tilt sensor if desired.

Initialization​

An RTK fix is required before tilt compensation can be initialized. Once an RTK fix is achieved, an initialization process is required to activate tilt compensation. As demonstrated in the video below, the user rocks the device back and forth until a beep is heard.

  1. Turn the device on
  2. Extend the pole to 1.8 meters (default, but can be changed via the Antenna Height)
  3. Enable NTRIP or other and obtain an RTK Fix (required)
  4. Rock the FPM-T back and forth 2 or 3 times
  5. Spin the FPM-T 90°
  6. Rock the FPM-T back and forth 2 or 3 times
  7. Once a beep is heard, the device is actively tilt compensating and work can begin
  8. The device will emit a beep every few seconds indicating it remains in tilt compensation mode

Accuracy​

When tilt compensation is active, the SparkPNT FPM-T fuses IMU sensor and GNSS RTK positioning data to deliver a compensated position. This does slightly increase the inaccuracy of the location readings. The amount of added inaccuracy is based on how tilted the device is when a reading is taken and is shown below:

Tilt AngleAdded Inaccuracy to Position
0° - 30°+/-1cm
30° - 60°+/-2cm

Altitude Compensation​

By default, the SparkPNT FPM-T outputs the location of the spot slightly inside the dome where the GNSS signals are received. This spot is accurate to a few millimeters when an RTK Fix is achieved. The SparkPNT FPM-T's 'location' as seen in the GIS app is this spot hovering above the earth. While tilt compensation is active the device continues to output the location of the spot slightly inside the dome as if the pole were completely vertical. A GIS app usually has a setting to input 'Instrument Height' which will subtract this altitude above the ground so that gathered points are points on the ground (not ~1.858m in the air). Alternatively, the device can compensate the altitude reading by subtracting the instrument height. Please see the Output Tip Altitude setting to enable this compensation. Enabling this setting will cause the SparkPNT FPM-T to subtract the APC + Pole Length from the tilt-compensated altitude, and report the tip altitude to the GIS app. This setting is generally only used when a GIS app does not have an 'Instrument Height' setting.

For more information about Instrument Height please see APC and NRP.