Dynamic Adjustment of Stereo Parameters for Virtual Reality Tools

Dynamic Adjustment of Stereo Parameters for Virtual Reality Tools

Felipe Carvalho, Daniel R. Trindade, Peter F. Dam, Alberto Raposo, Ismael H. F. dos Santos

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

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

Objective

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

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

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

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

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

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

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.

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

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

Dynamic Adjustment of Stereoscopy Parameters for Fly Navigation

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

Dynamic Adjustment of Stereoscopy Parameters for Examine Navigation

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