# To start an OmniSTAR survey

The steps for starting a survey using the OmniSTAR differential correction service depend on whether you are using OmniSTAR as part of an RTK survey, in a real-time differential survey, or on its own.

For more information on OmniSTAR, see OmniSTAR differential correction service.

To start an RTK OmniSTAR survey

1. Create an RTK survey style with the satellite differential set to OmniSTAR. See Rover options.

2. Start an RTK survey using this survey style.

   The Select OmniSTAR Offset screen appears.

   To relate the OmniSTAR positions to the RTK positions, you must measure the OmniSTAR offset between an RTK measured point and the same position measured using OmniSTAR. Before the offset can be measured, you must wait for the OmniSTAR survey to converge.

   To survey without the convergence delay, you can:

   - Measure the OmniSTAR offset later when the OmniSTAR system has converged. To do this:

     1. Tap Esc and continue surveying using RTK.
     2. To check to see if the OmniSTAR survey has converged tap and select Measure / OmniSTAR initialization.
     3. When the OmniSTAR survey has converged, tap Offset and then measure the OmniSTAR offset. See steps 4 to 10 below.
   - Initialize your OmniSTAR survey enabling you to continue surveying using the OmniSTAR signals if the ground‑based radio link goes down during an RTK survey. See Initializing an OmniSTAR survey.
3. Tap New.

4. From the Initialization point field select a previously measured point. Trimble recommends selecting the highest quality, most convenient RTK point.

5. Define the antenna.

6. With the survey receiver positioned at the Initialization point tap Start to measure the point.

   When the measurement is complete, the Trimble Access software computes the offset between the OmniSTAR position and the initialization point and applies this offset to the subsequent OmniSTAR corrected positions from the GNSS receiver, ensuring that the OmniSTAR positions are in terms of the RTK points.

   When OmniSTAR signals are being received, the radio icon changes to an SBAS/OmniSTAR icon , and RTK:OmniSTAR appears on the status line.

   - Tap to see the SBAS status. From the SBAS status screen, tap the Info softkey to see the OmniSTAR initialization details. The Info softkey is only available when you are in a survey.
   - Tap the Data link softkey from the SBAS status screen to access the Rover radio screen.

   - If the OmniSTAR solution is not converging as expected, you may need to wait longer for this to happen. If you measured an OmniSTAR offset when the precision estimates were high, or chose to use an offset with high precision estimates, then the OmniSTAR solution may not converge as expected.

7. Continue surveying.

   If the ground‑based radio link goes down during an RTK survey you can continue surveying using the OmniSTAR signals.

For subsequent RTK surveys using OmniSTAR and the same RTK base as before, you do not need to measure a new OmniSTAR offset. When you start the survey you will be presented with a list of previously measured offsets for the current base. Select an appropriate offset.

Tap All to see all previously measured offsets for all bases and then Filter to filter the list to display the offsets for the current base. You must select an offset for the current RTK base, or for another base that is in the same calibration. Tap Delete to delete an offset. Tap Clear to clear a previously selected offset.

To start a real-time differential OmniSTAR survey

To survey using real-time differential and OmniSTAR do this:

1. Create a real-time differential survey style with the broadcast format set to OmniSTAR. See Rover options.

2. Start a real-time differential survey using this survey style.

   When OmniSTAR signals are being received (and not RTK), the radio icon changes to an SBAS/OmniSTAR icon . Tap the SBAS/OmniSTAR icon to see the SBAS status.

If you subscribed for OmniSTAR HP, G2, or XP, the accuracy of your position after convergence will improve as the system converges.

To start a survey using OmniSTAR when RTK is unavailable

If you can't start an RTK survey you can start an OmniSTAR survey on its own. To do this:

1. Attempt to start an RTK survey configured to use the OmniSTAR system when RTK is unavailable.
2. Tap Esc. You will be asked if you want to cancel the survey or start an OmniSTAR survey without waiting for RTK.
3. Tap Continue to start an OmniSTAR survey.

4. Select an OmniSTAR offset. The selected offset is indicated by a tick.

   Because you have not yet received an RTK base, the offset list can not be filtered. You must select an offset with the appropriate base.

5. Continue surveying

   Later, if you are within radio range and the RTK base is detected, a New base detected message appears, enabling you to select the base and continue surveying using RTK.

To initialize an OmniSTAR survey

If you start a survey without RTK, or if the ground‑based radio link goes down during an RTK survey and you lose lock on satellites resulting in OmniSTAR losing convergence, you can manually initialize the OmniSTAR system. To do this:

1. Tap and select Measure / OmniSTAR initialization.

2. If you have not already done so, select an offset. The selected offset is indicated by a tick.

3. Tap Init.

4. From the Initialization point field, select a previously measured point.

   Trimble recommends that you select the highest quality, most convenient RTK point.

5. Define the antenna.

6. With the survey receiver positioned at the Initialization point, tap Start to measure the point.

   The OmniSTAR system will converge.

- This procedure is only available for OmniSTAR HP, G2 and XP subscription levels.
- If your RTK survey is running and an OmniSTAR offset is selected, OmniSTAR can initialize from the RTK survey automatically and this procedure is not necessary.
- Tap to see the SBAS status. From the SBAS status screen, tap the Info softkey to see the OmniSTAR initialization details. The Info softkey is only available when you are in a survey.
- The SBAS status screen shows the current Correction satellite name. To select a different satellite, tap Options and then select the required satellite from the list. You can change the correction satellite at any time; changing the correction satellite does not require restarting the survey. Alternatively, select Custom and then enter the frequency and bit rate to use. Changes you make to the settings are used the next time you start a survey.