Documenting Measurements and Data Management

One of the requirements presented in Sec. 2.2.1 is to improve efficiency of the work process and the documentation of measurements. This implies that the system needs a reliable and accessible persistent storage of the data produced by the application.

Persistent storage is storage of permanent data. [89].

6.2.3.1 Data storage

When the user starts the measurement process the application retrieves the required information from a file depending on the chosen panel. The information is stored in a plain text file and is not hard coded inside the application. The idea of this was to allow developers and users to update metrics like tolerance and position of points out-side of the application and even add new panels without having to redeploy the entire application. As of now the positioning of points demands some trial and error and the

parts only work for the composite panels that has been added and calibrated manually by the team.

In line with acceptance criteria XRI-181 (see Fig. 43) - when the measurements of a specific panel is saved, these measurements together with their respective point IDs is saved to a single Comma-Separated Values-file (CSV-file). CSV is a file type that separates fields of information with commas - the system use the common application as described in [90]. This file format was chosen because users can easily go into a document and view, or manually change different values without extensive knowledge of computers. The file type is also widely compatible with different text readers and can be opened in a popular spreadsheet reader, Microsoft Excel.

Figure 43: Acceptance criteria for saving the measurement data

From the users’ perspective the term ”directory” is a location for storing files [91]. Every time the micrometer register a measurement, the HoloLens takes a picture to document where the measurement were taken. From the users’ perspective the term ”directory”

is a location for storing files [91]. The file with measurements and a directory of the belonging pictures is stored unaccompanied in a directory, name of which is constructed using the panels ID, along with date and time of the storing. Looking at the directories - one level up from the directory with a measurement file, there is a directory listing all the directories with stored measurements that has been done on panels with this distinct Panel ID. One level up from this - all the panels ID’s which has measurements stored to them are listed, as seen in Fig. 44. This allows the user to locate and access previously stored sessions of measurements quickly, even when there are hundreds of

them. The directory structure is created as panels are measured and there are no empty, redundant directories. To extend the system any number of new panels can be added without changes to the file system or how measurements are stored.

Figure 44: Snapshot of the directories structure

When a measurement is sent from the micrometer to the XRI-application its value is evaluated on the application side. The measurement value is controlled to be inside the expected tolerance of that specific point (see Sec. 2.2.1). If the measurement is outside the tolerance - the system alerts the user in accordance to the acceptance criteria as seen in Fig. 45.

Figure 45: Acceptance criteria for marking a production error

The average value of the measurements taken for each point are stored as described in acceptance criteria in Fig. 46. At the same time, photo verifications are stored for every single measurement in accordance with the acceptance criteria in Fig. 49. Photos are named by its point ID and the time it was taken. This data is not moved into the persistent storage before the user uses the save instruction.

Figure 46: Acceptance criteria for comparing measurement values and storing the av-erage

For the user to retrieve measurement data from persistent storage, the user must use Windows Device Portal (WDP) - this application allows the user to access HoloLens files over network connection or USB [92]. Inside the applications installation directory there is a measurements directory which holds all of the measurement’s data.

6.2.3.2 Implementation of storage and data management

In the systems context which is to verify where a measurement is taken - a minor loss of image quality is acceptable in exchange for the reduced size. The images are stored as JPEG-files. JPEG was chosen since it provides compression of the images at a ratio of up to 10:1, uncompressed over compressed - with minor loss in perceptible image quality [93].

The code in fileHandlerprovides two functionalities - storing measurements and re-trieving a part. Store measurements takes a list of points and a panel ID and stores these to the appropriate location together with the belonging pictures - creating all necessary directories if needed. retrievePart()-functionality takes a panel’s ID and parses the information from that panel’s file and creates a list of points that holds all the data needed to perform a measurement on that panel.

There is a vast variety of options when handling files on Microsoft Windows operat-ing system and the resources on the web proves to be ambiguous and often hard to get working on HoloLens because of file access restrictions and deprecated solutions.

Plowing through these cost the team a lot of time. The group discovered two distinct ways to deal with files that work using Unity for HoloLens - Microsoft’s own API called Windows.Storage [94] and System.IO.File - the latter one is preferred according to an official blog post [95] by Unity, and thus has been the team’s choice as well. File access is restricted on HoloLens and there is no file explorer as on the common Windows Operating System used on the majority of PCs. Thus, all the directories and the CSV-files containing measurement data is created and stored within the installation directory.