Once geodetic data has been processed by Delta Watch, you can create virtual sensors based on this data. A virtual sensor could be a:
- Convergence line: For example, often used in tunnelling to calculate stress or 3D vectors between 2 points.
- Horizontal profile with multiple points: For example, on a sheet pile wall or a building that is being underpinned.
- Tilt sensor: For example, to get angular tilt data of a building.
All of the above sensor types have their unique properties and applications but also their own data output on which alarms can be set, reports generated, and data exported.
In this article, a virtual tilt sensor will be configured.
The virtual sensor modules are activated via a license add-on. If you cannot see the modules in your copy of Delta Watch, then contact your local dealer to obtain these extra modules.
To be able to set up a virtual sensor, you need to have at least some epochs with geodetic observations.
An understanding of setup and creation of local coordinate systems is assumed. For details, refer to this article.
- Configure a local coordinate transformation, one for each group of observations that needs to get the same orientation for the output of the virtual sensor.
- Create point groups containing only the geodetic sensors that are going to be used, one group per orientation. This step is optional but allows you to, for example, view and export the data easily.
- Load a background image into Delta Watch.
- Add a sensor in the Sensor fields section of the Structural monitoring module. Multiple virtual sensors can be created within a sensor configuration.
- Create an individual sensor, and load geodetic points.
- Configure the Calculation section.
- [optional] Configure alarms.
- [optional] Configure data export.
- [optional] Configure automatic reports.
Configure a local coordinate transformation
Tilt is calculated along the longitudinal. Most likely, the direction of expected movement from the two points that make up the tilt sensor is currently not in the right plane. Therefore, create a local coordinate system to rotate only the points used. Rotate it such that the direction of expected movement is along the longitudinal. See the below illustrations where a rotation transformation will be applied to achieve this.
From the images below:
- On the left is the current situation: Without applying a local coordinate system, the resulting output of the virtual tilt sensor A3 would not be meaningful.
- On the right: After applying a local coordinate transformation, the output of virtual tilt sensor A3 will relate to the expected movement of the building.
Further: Virtual tilt sensor A2 could be in the same local coordinate system, but A1 could be given its own transformation if the output needs to be in relation to the façade of the building. See the illustration on the right.
Once the local coordinate transformation has been created, it needs to be assigned to a point group. It is possible to skip this step, but by doing so, you cannot view the data in charts, create reports, set alarms, or export data with the correct alignment, so it is recommended to not skip this step.
Create a point group
This step could be skipped, but as mentioned before, there are some downsides in skipping. Therefore, create a point group that will contain only the geodetic observations that are going to be used for the virtual sensor. Create a new point group for each group of observations that needs to get their own local coordinate transformation. Tilt is always calculated along the longitudinal.
Load a background image
The Structural monitoring module requires a background image to work correctly. This image could help you visualize the location and movement directions. It can be any image and does not need to be orientated like you do with map backgrounds.
In Delta Watch, navigate to Administration > System configuration > Background image, and Add your image(s). Below is a screenshot of our background image loaded in Delta Watch. Now it can be used and re-used on various places, including for Delta Live!
Add a sensor in the Structural monitoring module
- Navigate to Projects > Structural monitoring, and Add a sensor field.
- Give it a general name. Remember, multiple sensors can be defined in a single definition.
- Select the Sensor configuration tab where sensor definitions can be added.
- Specify the processing interval. This should not be smaller than the epoch interval from the network where the points are processed. Setting this to a multiple allows for averaging in the data results.
- Select your background image.
Create an individual sensor, and load geodetic points
- In the subsection Profile configuration, click on Add , and a new dialog box shows. See the screenshot below.
- In this example, select Vertical profile for the Dimension to add a vertical tilt sensor.
- Select the earlier created transformation.
- Check the values that need to be calculated.
- Save the settings.
- Add Geodetic sensors by clicking on the Edit icon ().
- If you made a point group, it is simple to add your points. Make sure you only add the 2 points that will be used for the vertical tilt. Selecting more than 2 points would only make sense when creating a horizontal profile sensor.
- Repeat for any other sensors.
Configure the Calculation section
For Delta Watch to create the plots and calculate correctly, the points of each profile sensor need to be placed on a background image in the correct relationship, i.e., top-to-bottom or left-to-right.
- Select the Calculation tab.
- Check the Edit mode: set points box.
- Select from the Profile drop-down list the one to start work on. The label of the selected profile will be highlighted.
- Drag each point to the correct position on the background, keeping the real-life relationship between points in mind.
- When all points of all profiles are on their position, uncheck the Edit mode: set points box.
- Save changes by clicking Apply.
Below is an example of 3 tilt profiles placed on an image.
It is not possible to configure and set alarms directly in virtual sensors. Alarms can only be configured in the normal way directly on point groups using the Limit monitoring section in the Point and Limit management module.
Configure data export
It is possible to export some of the fields from the structural sensor. This can be done in the Import & Export module under Interfaces.
Below is a rough outline of what needs to be done. For more details, read Delta Watch: Import & Export module.
- Click on the Add button to add a new definition. A dialog box opens, see below.
- Configure the fields here, making sure the correct Export type and sensor are selected.
- If required, alarm messages for data flow can be configured.
- [optional] The user can define their own export format and filename structure to be used under Export type. This must be done before being able to select it here.
Configure automatic reports
Automatic reports are a great way of distributing results on a regular basis to various parties. Navigate to the module Analysis > Reporting to configure. The description and image below show how to do this.
- Open the Automatic reports branch.
- Click on Add . A dialog box shows where you can give this report a name.
- Now various fields need to be configured:
- Sensor field: Select the sensor as created earlier.
- Output path: Where the PDF report will be saved.
- Start time: Date/time when the first report should be generated.
- Time interval: How often the report should be generated.
- Time span: What time period the report should cover.
- [optional] Configure emailing: This will email the actual report, NOT a download link.
- Apply the configuration.
Viewing the data
Data of the virtual sensor created can be viewed from within the module where it was created on the Calculations tab. Here, one can see the calculated values for a specific time or over a timeframe, depending on the sensor type. In the case of the virtual tilt sensor, the user can specify a date/time:  Select the sensor.  Scroll backward/forward in time  with steps as defined in the Sensor Field configuration in the field Processing interval. The results  will automatically update.
If a specific point group was created with its own local coordinate system applied, then it is also possible to see the Delta displacement of the observations used in the direction of movement as required. This makes it easy to set alarms or create graph reports. Below is an example of the same observations used for creating the virtual tilt sensor.
Top chart: No coordinate transformation applied. X and Y directions both seem to move.
Bottom chart: Specific transformation applied to rotate such that the direction of interest becomes the longitudinal, or X direction, in this specific case.