Last year I worked on a group project developing an application designed for mobiles that was meant to demonstrate a "3D effect", the idea being we could bring 3D virtual reality to the masses via smartphones and gyroscopes. The main inspiration for our client was a video of a ballerina inside of a box. The video can be seen below.
From this vague description we were to research and make our own application that demonstrated a similar style of 3D effect. During the project we went through several different iterations and drastically different ideas before the final product was implemented. The first view versions focused mainly on being a game where you fly around the universe, go to different planets and space stations and witness all sorts of interesting and scripted events. Sadly when we approached the client with what we had made the 3D effect wasn't so good or prominent due to the set up of the scene. This resulted in a big change where we decided to try and create a holographic projector type set up.
A video of the application so far can be scene below:
To get this effect we made use of camera distortion technique known as the offset projection matrix. This is where the camera view frustum is distorted allowing various visual effects to be achieved. A regular view frustum is uniform in shape as can be seen in the image below.
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| Figure 1 - Example View Frustum |
The view frustum in most cases is defined simply by the distance and sizes of the far and near planes, they are usually centre aligned and thus symmetrical giving all the objects in the world the correct appearance. For our phone application the users perspective relative to the phones screen has changed, what we wanted to do in this case was alter the frustum relative to the rotation of the phone so that we maintain the users perspective and distort the objects in a manner which would be correct from their point of view.
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| Figure 2 - Far plane shifting (I apologise for the use of paint) |
In the above image we can see how the far plan must be shifted relative to the users position where the near plane is fixed and still parallel with the far plane. This is required because of the users change in position, simply rotating the camera on it's axis will not achieve the required distortion, feel free to attempt this and you will see exactly what I mean.
The only major problem that was not solved over the course of this project was the drift caused by the gyroscope on the mobile device. This drift meant that when the phone was righted back to it's original position it wouldn't quite be right or perhaps when rotating upon any axis it would detect false movement ruining the illusion if the application was used for too long. For just now we implemented a reset button that allowed the user to reset the view which helped alleviate most of the problem. As well as this I kept meaning to add in more of the application to bring it up to a complete level, the original idea being to create an "educational, hologram viewer" application, this would include information about each object that was shown but this is still a work in progress whilst I am at University.
Anyways thanks for reading. I will upload an APK of the application when I can.
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