Delta Link: Station relocation function

Sometimes during the life of a monitoring project, the total station needs to be moved to maintain sightlines to prisms.

DeltaLog 2.x provides a relocate function that will greatly simplify this process.

This document guides you step-by-step through the relocate process.

The relocate function should NOT be used for:

• Setting the horizontal angle of a station when it comes back from service. Use the Set Hz tool for this.
• Adjusting angles after releveling of the station. The Searchwindow settings and 3D checks values should be sufficient.
• Any other action where the mounting position of the station has not changed.

The relocate function calculates and applies a transformation between the old and new station location based on the observation data from 3 points visible from both the old location and the new location.

• Choose points that are equally spread out over the monitoring site, both in horizontal and vertical planes and that represent distances compared with the rest of the observations.
• Have more than 3 points in case line of sight issues or residuals are not acceptable.
• Verify and update ALL observations just before taking down the station from the old location. Re-level the instrument if required/possible before doing this.
• Perform a field calibration on the instrument just before placing it in the new mount position.
• Adjust or rename the Station ID to mark a clear separation in datafiles, etc.
• Verify/update, and deactivate where required, all observations from the new position.

Before you start, assume the following:

• The operator is familiar with operating and controlling the Delta Link unit.
• The operator knows how to and can perform a station field calibration.
• The operator is familiar with Delta Watch.
• Total station and Delta Link have been set up and are actively monitoring.
• Delta Watch is processing the data.
• A new location is identified for the station and a check was done to see which reference/common prism can (possibly) be seen to be used for the relocation calculation.

1. Identify a minimum of 3 observations that can be seen from both the old and new locations.
2. At a minimum, verify and update these observations just before taking down the old location. It is best to update ALL observations.
3. Install the station and Delta Link on the new location.
4. [optional] Adjust or change the name of the station in DeltaLog.
5. Start the relocate tool, and use it with 3 of the observations from step 1.
6. Start monitoring again.

There are additional steps that can be done for best results. These steps will ensure that:

• All targets are verified so that observations can be disabled if there is no line of sight. This will save monitoring time, reduce wear and tear of the instrument, and consume less power.
• Accurate angles and distances are used so that any 3D check can be performed correctly and monitoring speed is not adversely affected.
• The Delta Watch Point and Limit management table is updated with new coordinates for the station position.

7. Verify and update at a minimum all reference and common observations. It is best to update all observations.
8. Deactivate any observation that could not be made.
9. Recalculate the station position in Delta Watch, and update the Point and Limit management table with this information.
10. Update the WGS84 coordinates for Delta Live! for all affected items. Update Delta Link STNI, THP, and CUI as well as the station position itself.
11. Add a note to the total station position at the date/time for both the old and new positions.

The workflow described here will apply best practices to achieve best performance for the complete setup. It is up to the operator to ensure the right decisions are taken.

Preparation: On site

1. Identify a suitable new location for the total station, and, where possible, verify which points can be seen and used for the relocate function without having to adjust the actual prism for best sighting line. It is best to have a set of more than 3 points that can be used. This is in case a combination might not give good results (residuals).
2. When possible, prepare the new location before taking down the old.

Preparation: In office

1. Prepare the Delta Watch Point and Limit management table (PandL) by adjusting the Station ID. In the PandL table, copy the current station record and adjust the name to reflect the new Station ID. For the moment, the current coordinates can stay the same. This step of creating a new Station ID is important if the station is a fixed point. In such a case, it is very important to calculate new coordinates for the station before continuing automated processing once the new location is up and running.
2. Print out a map view that shows all the point locations and their names.
3. Mark on the same map the new station location and name (Station ID).
4. Mark the points that should be used for the relocate calculation.
5. Log on to the Delta Link unit, and check for any software updates. You need at least DeltaLog 2.0 for the relocate function to be available.
6. Deactivate any point that has not been measured for some time. Do this by analyzing the monitored points from the station over a period of several days. The observation data files (OBS*.DAT) are ideal for this.

Decommissioning the old station location

Before decommission, there are a few actions that need to be done. Some can be done from the office or locally when in the field.

1. Check the station bubble and re-level if possible.
2. Verify, at a minimum, the points that have been identified to be used for the relocate calculation. Do so using the DeltaLog Turn To and Check functions, and always update the data by clicking on Use New Values. Refer to the image below.
3. We strongly advise you to verify ALL other active observations. This will give the best result when calculating the new set of angles and distances.
4. Shut down the Delta Link unit and the total station, making sure DeltaLog is NOT in monitoring mode.
5. Make a note of the date/time when the monitoring was stopped so that a note can be added to the last epoch taken from this location.

Commissioning the new location

1. Perform a field calibration on the instrument. Refer to the instrument's manual for how to do this.
2. Level the tribrach before installing the instrument, and then level the instrument up.
3. Roughly check if and which of the selected points for the relocate function can be seen. You do not need to measure them—only a rough check of the sight lines is sufficient.
4. Connect to the Delta Link unit, and open DeltaLog.
5. Alter the Station ID in the top left of the main screen of DeltaLog.
6. Use the Connect button to turn the station on and check if it can communicate.
7. Navigate to Settings > Tools & Info, and click on Relocate Station.

8. Select your first Target (left image), and click on Add (right image). Repeat this for the other 2 targets.

9. Once 3 targets have been selected, click the Start button (left image). The quick support text updates to tell that you need to manually aim the total station to the first point in the table. At this time, you can turn on the laser pointer of the instrument by clicking the Laser checkbox at the bottom left.
10. Once aimed, click the Find Target button (middle image) to let the station search and measure the point.
11. Repeat the aim and measure for the other points, and then click Confirm that you want to continue (right image).

12. DeltaLog will now calculate the transformation and show the results (left image). If all went well, the residuals are very small: centimeters or less. Click Transform to complete the process. If errors were not acceptable, then the following might resolve this:
    
    1. Repeat the process, and make sure the correct targets are used, both in the list and when measuring.
    2. If errors stay high, use one or more other points. It is best to replace a point one-by-one to eliminate the bad observation. Avoid using points that are:
       • 180° opposite relative to the station
       • are situated close to each other
       • are only on one side of the station
       • have very small angles between them
    3. Was the field calibration of the station performed correctly?

13. All observations are now updated with new angles and distances. If your residuals were (almost) zero, then it should be no problem to aim correctly to all observations. However, because of the location change, some points might now have line-of-sight issues or, due to the angle between prism and total station, can now not be found/measured. It is also possible that a previously blocked prism can now be measured. For best results, it is strongly advised to perform a validation on all prism and sheet target observations. To do so:
    
    1. In the main screen of DeltaLog, select the first point in the list and perform a Turn to, Check, and Use New Values action.
    2. If the point could not be found, make an assessment as to why this is:
       • line-of-sight issue. Either resolve it, or mark the point as not active.
       • invalid angle between prism and total station. Adjust the prism orientation to be sighted correctly again. Make a note of the location so that in Delta Watch, offsets can be applied if needed.
    3. Repeat the steps for all the other points.
14. When it has been verified that all points can still be measured and their values have been updated, the automated monitoring can commence again.

If Delta Watch was previously prepared to accept the new Station ID, then automated processing should not fail. If the station was configured as a fixed point type, then this will lead to big errors in the calculations and even movements of monitoring prism. Either way, it is good practice to use the first data set(s) to calculate just the new station position and update the PandL table with it.

Station is of type: Object point

Navigate to the first automated epoch calculated with the new data set, and examine the network adjustment results. If these are acceptable or no different than before the relocation action, then you could update the station coordinates in the PandL table directly from this epoch by navigating to Coordinates > Output coordinates.

1. Open the Output Coordinates tab, and locate the station.
2. Right-click on the station entry, and select Write coordinates in point definition.

Delta Watch will now use these coordinates as approximate coordinates next time when it performs a calculation.

Station is of type: Fixed point

In this situation, you need to recalculate the network to get a new coordinate for the station position. This is not an ideal situation, as the station was most likely one of just a few reference points to be able to calculate.

1. If Delta Watch already did attempt to calculate an epoch with the new position, then navigate to this epoch, and create a manual epoch from it by clicking on the copy icon while the epoch is selected.
2. Navigate to the manual network to which you just copied the epoch, and select it.
3. For better results, you might want to import some extra data:
   
   1. Open the total station data section, and click on load measurements.
   2. Select a few more data files with data from the new station position.
   3. Calculate and apply the settings.
4. Navigate to the epoch, and make a selection of points, making sure the affected station is NOT a datum or reference point.
5. Perform the network adjustment for both horizontal and vertical, and check the results.
6. If results are acceptable, then write the new coordinates for the station to the PandL table. Open the Output Coordinates tab, and locate the station.
7. Right-click on the station entry, and select Write coordinates in point definition.

The basic configuration is now adjusted in Delta Watch, and automated processing can continue.

If you have configured things like:

• Point groups with the station included
• Alarms on the station position or its data flow
• Map views
• Delta Live!
• Data or report exports

then each of these items needs to be reviewed and adjusted to handle the new position, e.g., WGS84 coordinated for Delta Live!, and/or the new Station ID.