Mobility Lab is designed for brief, clinical assessments of pre-defined tasks (e.g., the Timed Up and Go, or the 2-minute Walk). In almost all environments, it is desirable to capture the data using the Wireless Streaming Mode, where you can instantly view the analysis results for your recorded trials. Under some circumstances, however, it is not optimal to collect data using the wireless streaming mode. For example:
- You are trying to capture a Walk trial in a subject's home and bringing and setting up a laptop for the wireless data capture is not possible due to time and/or space constraints.
- You are recording data in an environment with severe wireless interference
- You are recording data where the subject may be at a distance and cannot be close to the access point at the beginning of each trial to initiate the recording or at the end of the trial to stream the recorded data
While not seamlessly integrated into the Mobility Lab workflow, it is possible to capture data using the Synchronized Logging mode of data collection and to then import these recordings into Mobility Lab for analysis and reporting. Below, we describe the process of configuring your system for data collection in the Synchronized Logging mode.
Assigning the correct labels to the sensors
If you wish to use the logged recording as a Mobility Lab trial, the labels on the sensors (e.g., "Right Arm" must be set correctly so that the algorithms know where the sensors were placed. The easiest way to assign the correct labels to the sensors is to first configure your Opals in Mobility Lab following the standard configuration procedure.
Configuring for synchronized logging mode
1. Switching to the Motion Studio view
To configure for recording in the Synchronized Logging mode from within Mobility Lab, navigate to View→"Motion Studio View", which will result in a change in the user interface. You can return to the Mobility Lab view at any time by navigating to View→"Mobility View". See the screenshot below, which displays the Mobility Lab configuration screen and shows the menu option to switch to the Motion Studio view.
2. Opening the Motion Studio Configuration Dialog
From the Motion Studio view, click the Configure button on the left of the toolbar. Because the system was already configured from within Mobility Lab, all Opals are ready to be placed into synchronized logging mode by selecting the option from the "Record Mode" drop down menu (screenshot below). Click the Configure button to configure the Opals to record in the Synchronized Logging mode (screenshot below).
Recording logged data
The Opals will begin recording as soon as they are undocked and will continue recording until the battery runs low or they are connected to a dock or power supply. When all Opals have been undocked, they will wirelessly synchronize with each other. Their logged data can later be converted merged into a single, multi-Opal HDF file that can be used in Mobility Lab.
Processing your logged data
1. Selecting logged data for conversion to HDF format
When data collection is complete, return all Opals to the docking station, and click the Import button in the toolbar. The screen will show you logged data that is available for conversion to HDF. It will search the contents of any docked Opals and your logged data backup folder. Select the recordings you would like to convert for analysis. When selecting a recording from the list, any additional recordings from the same time period will be highlighted, making it easier to identify all sensors used in a synchronized recording event.
2. Converting the entire logged recording into a single HDF file
For some users, having the complete logged recording is desirable. If this is your use case, you can simply click on the "Convert" button, which will extract the regions of the selected recordings that overlap with each other. This results in a single, multi-Opal recording in HDF format where each Opal has the same number of recorded samples and they are all synchronized (i.e., the nth sample from Opal X occurred at the same time as the nth sample from Opal Y). Do not disconnect the Opals from the dock/computer, or close the application while conversion is in progress. When complete, the resultant file with appear in your workspace under Mobility Lab Project, and can then be exported to CSV or another application.
- Note: there is an option in the configuration dialog that states "Convert all data in the selected files, and not just the range where their timestamps overlap". Do NOT select this option, as the analysis of these files will be inaccurate. The algorithms expect synchronized recordings from each Opal in the resulting HDF file that start and stop at the same instant.
- Note: Mobility Lab's algorithms are tuned for relatively short assessments. Analyzing Walk trials that exceed 10 minutes in duration may be inefficient, and take a long time to analyze.
3. Segmenting logged data for use as a trial in Mobility Lab
If you intend to use logged data recordings with Mobility Lab for analysis, "segmenting" the data to align with a prescribed test type is required. This is because the Opals start recording as soon as they are undocked and record until they are docked again. Without segmenting, you will be analyzing the entire recording, including putting the sensors on the subject and removing them from the subject.
There are a few ways to identify the correct segments of logged recordings, but the goal is to extract segments of the recording that correspond to the Mobility Lab trial you are attempting to perform. A few ways to identify the correct data segments are:
- Button events: The most foolproof way to identify the trial segments is through the use of button events. A single Opal can be configured to have each button act as a trigger to write a user defined text string to the annotations field of the recording, along with a precise timecode stamp to indicate the event. As an example, button 1 could write "StartTrial" to the annotations field to indicate the beginning of a trial, and button 2 could be configured to write "StopTrial" to indicate the trial event has ended. These button events are recorded along with the inertial data and can be used at the time of import and conversion to specify the segment corresponding to your trial. Configuring an Opal log button events does not interrupt normal function and can still be used to gather inertial data.
- Computer clock: The Opal's internal clocks are set at configuration time, and should closely match the clock on the computer used for configuration. When a subject performs a trial, note the time (to the second) of the start and end. You should use the clock on the computer used for configuration for this task, or another clock that is set identically or has a known offset. These times will be used when the data is imported and converted into a trial.
- Visual inspection: You can have the subject perform some type of easily identifiable movement indicating the beginning and end of a trial. For example, you can the subject clap 3 times a fixed duration (e.g., 3s) before the start of the trial and after the end of the trial. You can then initially import the complete recording and locate the time stamps of these events by visual inspection of the raw data (in the clapping example, the right and left arm sensors would display 3 sharp peaks at the same time). You would then re-import the trial specifying these time stamps, deleting the original trial when complete. This approach is particularly tedious, but is included here for completeness.
Select both the "Custom Start Time" and "Custom End Time" options to specify either button events or clock time to segment the file. Once the data segment has been identified, click the "Convert" button to create a single file that contains the recordings of all selected sensors. The resultant file can now be imported as a trial in Mobility Lab to be analyzed.
4. Importing your logged recording into Mobility Lab
Navigate to View→"Mobility View" to return to the Mobility Lab interface. Navigate to the subject that corresponds to the data set, and from the cog menu in the upper-right corner, select "Create Trial from Recording". Select the test type and condition that was performed, and then select the "File" icon to locate the file converted earlier in this step. Mobility Lab will now import the segmented data as a trial, and return to the "Subjects" view. Select the subject to view all completed trials, and select the imported trial to view the analysis.