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HW1: VR Cardboard Setup and Calibration

Due date: 2024-08-16 23:59.

Why calibration is important

For those using the VR Cardboard in this course, this section will guide you through the necessary setup and calibration process. Calibration is crucial for any VR headset to ensure an optimal user experience, especially with the Cardboard. Unlike higher-end head-mounted displays (HMDs) that often include a guided, mandatory calibration process, the responsibility to accurately set up the Cardboard lies entirely on you. Proper calibration is not only essential for your comfort but also for ensuring that you get the most out of the course materials and homework.

For High-End HMD Users

Although we will not guide you through the process on your HMD, it is crucial that you perform the calibration procedures recommended by your HMD’s manufacturer.
Additionally, please complete the exercises below using your smartphone only. This will help you understand the calibration process that applies to most modern VR HMDs (likely including yours). Be sure to answer all questions as accurately as possible. For the best experience, we recommend purchasing a VR Cardboard to fully benefit from the calibration process.

Setting up Calibration Parameters

It is important that you complete the following steps in this recommended order.
On your PC:
  1. Begin by following the link to the VR Cardboard calibration site: Google Cardboard Viewer Profile Generator
  2. Scroll down on the page you will see the VIEWER PARAMETER FORM.
  3. Fill out the form fields for Your Company and Viewer Name with the appropriate values.
  4. For the Primary button type, select None.
  5. The rest of the parameters in the form will greatly impact your viewing experience and comfort. The exercises on this page will help you set them up appropriately and optimally.
  6. This additional reading may help you along the way: Google Cardboard Instructions.
On Your Smartphone:
  1. Compute the PPI of your smartphone screen (before opening the link in the next step). The first exercise below will help you compute PPI correctly.
  2. Open this link on your smartphone: https://wwgc.page.link/pLZEV. It will immediately ask you to input the PPI value that you just computed.
  3. Once you complete the above steps, your PC will couple with your phone viewer, and as you change the parameters on the PC form, the app on your smartphone will reflect the changes.

Question 1: Screen Size and PPI

To compute your phone's PPI (pixels per inch), you need the screen resolution and the screen size. Follow these steps:
  1. Find Your Screen Resolution: Check your phone’s specifications or search online for your phone model’s resolution, W x H (e.g., 1080x1920 pixels).
  2. Find Your Screen Size: Measure the diagonal size of your screen in inches.
  3. Use the PPI Formula:
PPI = \frac{\sqrt{(\text{W}^2 + \text{H}^2)}}{\text{Diagonal Size}}
For example, consider a phone screen below:
If the screen diagonal size is 5.66 inches and the resolution is 1080x1920 pixels, then the resulting PPI would be:
PPI = \frac{\sqrt{(1920^2 + 1080^2)}}{5.66} = \frac{\sqrt{3,686,400 + 1,166,400}}{5.66} = \frac{2202.91}{5.66} \approx 389
Note: Please do not rely on PPI information from the web, as the reported values, even from manufacturers, may differ from your calculations.
Now, enter the resulting PPI in the textbox below. Then continue with the steps on your smartphone.

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Question 2: Screen to Lens Distance (mm)

The Screen to lens distance (mm) parameter is crucial for the VR rendering engine to match the viewing angle to normal vision. Incorrect settings can cause objects to move unnaturally, reducing immersion and potentially causing motion sickness. This parameter depends on factors like the distance between the screen and the lens's optical center, screen thickness, eye to lens distance, and lens magnification. Proper calibration is essential but challenging to measure manually.
To pick the best Screen to Lens Distance, you will first need a ruler to perform manual measurements. Measure the distance between the lower curvature of the lense to the display in mm and set it in VIEWER PARAMETER FORM.
Note: To test if the setting is correct and adjust it if needed, view the app in your VR Viewer. While exposing one of your eyes to your surroundings, keep the other eye on the screen image. You have to tilt the headset about 45 degrees pushing one side up, away from one of your eyes. Depending on the VR headset, this can be easy or hard to do. An incorrect setting can cause objects in virtual reality worlds to move at a pace that does not match your visual expectations, potentially causing significant strain and discomfort in your future VR experiences. You may leave this experiment for after you set up other parameters, but make sure you come back and perform it, to finalize the Screen to lens distance (mm) correctly.
Please type the value you saved in the VIEWER PARAMETER FORM into the textbox below.

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Question 3: Inter-lens distance (mm)

The next parameter to set is Inter-lens distance.
When you view the grid room in your VR viewer on your smartphone, you see a pair of red circles that are not necesarilly merged into one. In this case you need to start decreasing the value of Inter-lens distance on your PC in the VIEWER PARAMETER FORM, until the first comfortable value when the red circles become one. You have to determine the highest value at which the circles appear as a single, undoubled image, while ensuring it is comfortable.
If the circles are already merged when you try this exercise, then try increasing the values to the highest most comfortable maintaining the single, undoubled image.
Yes, it is extremely awkward to change the parameters in the VIEWER PARAMETER FORM while wearing a blindfold. Unfortunately, we do not have any recommendations to make this process easier.
Note 2: It is important that you double-check this number manually, by measuring the distance between the centers of the lens of your viewer with a ruler.
Please type the value you saved in the VIEWER PARAMETER FORM into the textbox below.

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Question 4: Tray to lens-center distance (mm)

In this exercise, you will set the parameter that determines the correct height perception in VR. In your VIEWER PARAMETER FORM it is called the Tray to Lens-Center Distance (mm).
  • Screen Vertical Alignment: First, select which side of the smartphone you will be measuring the vertical center from in the Screen Vertical Alignment selection. Choose either bottom or top (do not select center, as it is more awkward to work with).
  • Setting the Parameter: This is a perceptual exercise, and manual measurements may help only slightly, depending on the shape of your lens. You need to adjust the value in the VIEWER PARAMETER FORM until the red circle is strictly in the middle of your virtual view while wearing the headset. It may be helpful to imagine concentric circles of increasing sizes emanating from the red circle that need to all be fully in your field of view.
Please type the value you saved in the VIEWER PARAMETER FORM into the textbox below.

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Question 5: Distortion coefficients, k1

To properly set up the Distortion coefficients, k1 value, increase or decrease the values in the VIEWER PARAMETER FORM until all of the lines in the inner part of your view appear straight, without any apparent curvature.
Please type the value you saved in the VIEWER PARAMETER FORM into the textbox below.

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Question 6: Distortion coefficients, k2

To properly set up the Distortion coefficients, k2 value, increase or decrese the corresponding value in the VIEWER PARAMETER FORM until all of the lines in the outer part of your view appear straight, without any apparent curvature.
Please type the value you saved in the VIEWER PARAMETER FORM into the textbox below.

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Question 7: Field-of-view Angles

The final step is to set up the Advanced viewer parameters -> Field-of-view angles to maximize your peripheral vision while avoiding unnecessary rendering on the screen that is not visible through your VR Cardboard.
Once you have determined the best values, please enter the Outer, Inner, Top, and Bottom angles in the textbox, separated by commas:

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Question 8: Generate Your QR Code

You are almost set! Now go back to Question 2 to make sure you selected the best possible screen to lens parameter. Complete this step as many times as needed, to ensure optimal calibration.
Once you are happy with what you see in the viewer app, click Generate Profile button! Once your QR code is generated, take a screenshot, and save it for future use. You may need to use it when you open various VR apps.
For this exercise, please upload the saved screenshot as a .jpeg file to Google Drive or a similar cloud service. Then, copy and paste the link to the uploaded file into the textbox below for submission:

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Question 9: Did You Succeed?

The most important outcome of the above exercises is to create calibration parameters that make viewing VR content comfortable. Did you succeed in accomplishing this? Does the virtual world move and behave the way you expected, without making you feel nauseated or dizzy? Are you happy with this calibration? How many tries did it take you to achieve the most pleasant result?
Also, compare your custom QR code with the QR code provided by the manufacturer of your headset. Which one is better?
Please describe your experience of completing this exercise in 1-2 sentences.

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Question 10: Smartphone and Headset Information

Many of our course activities involve 360-degree experiences, making it essential for your smartphone and VR Viewer/Cardboard to meet certain specifications. Below is an example of the minimum specifications needed to ensure a satisfactory experience in this course.
Please provide the following details for your setup:
  • Smartphone Model: (e.g., Samsung Galaxy S8)
  • Operating System: (e.g., Android 8.0 Oreo)
  • API Level: (e.g., 26)
  • VR Viewer: (e.g., Google Daydream, Google Cardboard)
You can find most of this information in your device's Settings under About Phone.
Note: For students using their own high-end HMDs, please specify the model.
Please submit your response in the textbox below:

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Authors

Anna LaValle, Elmeri Uotila.
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