Dynamic Adjustment of Stereo Parameters for Virtual Reality Tools

1. Dynamic Adjustment of Stereo Parameters for Virtual Reality Tools Felipe Carvalho, Daniel R. Trindade, Peter F. Dam, Alberto Raposo, Ismael H. F. dos Santos

2. Introduction • Currently new stereoscopic technologies are increasingly present in our lives, reaching new areas, among which are virtual reality, cinema and games • However the use of stereoscopy may cause problems such as nausea and headache if the parameters aren’t set correctly

3. Introduction • Problems related to stereoscopy: • Objects with a high parallax value (positive or negative) cause discomfort because the eyes have a hard time converging • When the zero parallax plane isn’t on the same plane as the screen (accomodation/convergence problem) • Objects being clipped by the screen borders when they are in negative parallax • In multiscale environments, if the stereoscopy parameters are kept constant throughout the scenario, the convergence problem may occur

4. Objective • This work’s objective is to propose a solution capable of dynamically adjusting the stereoscopy parameters for virtual reality applications, including multiscale scenarios

5. Cubemap • Provides information about the virtual environment at a certain moment • Given a camera position, this structure is built doing 6 rendering passes, each one in a different direction so to cover the whole environment • Camera’s FOV is 90 degrees, so the combination of 6 resulting frustrums yields a cube • A shader is used to calculate the distance of the generated fragment to the camera, which is stored in the alpha channel • The cubemap images’ RGB channels store a unit vector originating from the fragment and pointing to the camera

6. Navigation Techniques • The way the user interacts with the scene may influence the stereoscopy effect • The stereoscopy parameter adjustment should consider how the user navigates and interacts with the scene • In this work we consider two interaction techniques: • Fly – free navigation through the scene • Examine – visualization centered upon a selected object

7. Navigation Techniques • The Fly navigation speed is automatically adjusted based on minDist (smallest value yielded by the cubemap for a certain camera position) • This way the navigation speed is in accordance to the scale in which the camera is in • Collision detection avoids the camera going through objects: every time the camera gets near an object it suffers a repulsion factor which makes it swerve gently • The clipping planes are also adjusted according to minDist to guarantee their correctness

8. Clipping Planes • The adjustment avoids objects being unduly clipped or the appearance of artifacts in distant objects, hindering the stereoscopy effect • Using minDist from the cubemap we are able to obtain optimal values for the near and far planes, keeping the visible geometry between the planes • We update near and far using the equation below, where n is the near plane, f is the far plane, alpha, beta, A, B and C are constants • C establishes a ratio between near and far • In our tests we found that the following values produce good results: • Alpha = 0,75 • Beta = 1,5 • A = 2 • B = 10 • C = 10000

9. Dynamic Adjustment of Stereoscopy Parameters for Fly Navigation • The stereoscopy parameters are dynamically adjusted using the following equations: • Distpzero = minDist • Eyesep = k * minDist • Where Distpzero is the distance to the zero parallax plane, Eyesep is the virtual eye separation, minDist is the smallest value yielded by the cubemap and k is a constant • This adjustment is done every time the clipping planes are adjusted

10. Dynamic Adjustment of Stereoscopy Parameters for Fly Navigation • The first equation creates an effect where the objects stay in positive parallax during most of the time, creating a more comfortable depth effect • The use of minDist avoids objects in negative parallax being clipped. It’s as if we could predict if an object will enter the camera’s visible area • It doesn’t matter if the user rotates the camera, minDist depends only on the camera’s position. This way a camera rotation doesn’t change the stereoscopy parameters.

11. Dynamic Adjustment of Stereoscopy Parameters for Fly Navigation • The second equation adjusts the eye separation according to the scale in which the camera is at a certain moment • For example: if the camera is in a room it may be reasonable that the eye separation is in accordance to the eye separation of a real person, however if the camera is looking at a whole planet, the eye separation must be changed to a larger scale • The constant k is chosen to provide a comfortable depth sensation to the user. In our tests we found that using k = 0.01 gives a satisfactory effect

12. Dynamic Adjustment of Stereoscopy Parameters for Fly Navigation • The proposed adjustment depends on the navigation techniques previously implemented due to the following reasons: • For the adjustment to work correctly the values of minDist must vary smoothly. This is possible due to the automatic adjustment of navigation speed • The collision detection guarantees that the stereoscopy effect will not be broken because the camera does not pass through objects

13. Dynamic Adjustment of Stereoscopy Parameters for Fly Navigation

14. Dynamic Adjustment of Stereoscopy Parameters for Examine Navigation • In this approach we decided to place the zero parallax plane in the center of the selected object • The eye separation is determined by a constant multiplied by the object’s bounding box. In our tests we set the constant to 0.18 • This adjustment produces an interesting stereoscopic effect since half the object is in the negative parallax while guaranteeing that it will not suffer clipping from the screen’s borders

15. Dynamic Adjustment of Stereoscopy Parameters for Examine Navigation

16. Conclusion • In our informal tests we have verified that the proposed adjustments produce comfortable stereoscopy and facilitates the use of stereoscopic virtual reality applications since the user does not need to worry about adjusting the parameters. • As future work we intend to conduct more accurate usability tests to evaluate our solution