Web-based Volume Rendering using Progressive Importance-based Data Transfer

Abstract

WebGL 2.0 makes it possible to implement efficient volume rendering that runs in browsers using 3D textures and complex fragment shaders. However, a typical bottleneck for web-based volume rendering is the size of the volumetric data sets. Transferring these data to the client for rendering can take a substantial amount of time, depending on the network speed. This can introduce latency that can in turn affect interactive rendering at the client. We address this challenge by introducing a multi-resolution bricked volume rendering, where data is transferred progressively. Similar to MIP-Mapping, the volume data is divided into multiple levels of detail. Each level of detail is broken down into bricks. The client requests the data brick by brick starting with the lowest resolution and renders each brick immediately as it is received. The 3D volume texture is updated as bricks with higher resolution are received asynchronously from the server. The advantages of this algorithm are that it reduces latency, the user can see at least a reduced-detail version of the data almost immediately, and the application always stays responsive while the data is updated. We also implemented a prioritization scheme for the bricks, where each brick can be assigned an importance value. Using this information, the client can request more important bricks first. Furthermore, we investigated the influence of data compression on the transfer and processing times.