EG UK Theory and Practice of Computer Graphics (2008) Ik Soo Lim, Wen Tang (Editors) A Haptic Rendering Algorithm for Drilling into Volume Data Y. Liu S. D. Laycock School of Computing Sciences, University of East Anglia Norwich, NR4 7TJ, UK Abstract With the developments of volume visualisation technology for complex data sets comes new challenges in terms of user interaction and information extraction. Volume haptics has proven itselfto be an effective way of extracting valuable information by providing an extra sense from which to perceive three dimensional data. In this paper, a novel indirect haptic rendering method using a Marching Cubes algorithm is presented for volume data removal. A novel three-step haptic rendering method is presented, which can be used to provide continuous and smooth force feedback during the drilling of various types of volumetric data. Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Geometric algorithms 1. Introduction Volume visualisation has become widely utilised for appli- cations such as Virtual Training [HBS97] and Scientific Visualisation [IN93]. The ability to visualise volume data directly is particularly important for medical applications where a correct anatomical view of the patient can prove vital for surgical planning. In this paper, a novel approach to drilling into surfaces based on the volumetric data is pre- sented. One of the major considerations of any application incor- porating haptic feedback is the rate at which the calculations must be performed. An update rate of 1KHz is required in order for a user to perceive stable and smooth haptic feed- back from the system. This is in contrast to the visualisation which must update at approximately 30Hz. One objective of this work is to create a system which can accurately render volume data at sufficient rates for both the visualisation and the haptics. There are two threads accessing and modifying the same set of volume data. To ensure a thread-safe implementation a novel three-step haptic rendering algorithm is employed to avoid accessing the same area of memory at the same time. 2. Related work Volume haptic rendering techniques can be categorised mainly into two classes. The first is direct volume haptic ren- dering, which computes the force feedback according to the information stored in the voxels. The second class is surface- based or indirect haptic rendering, which extracts an inter- mediate geometric representation of the volumetric datasets such as an iso-surface. The Marching Cubes algorithm is commonly used for extracting a surface from volume data. This method first partitions the volume data into voxels. The corners of each voxel are labelled exterior or interior depend- ing on the eight neighbouring volumetric data points. The surface configuration of each cube is then described by 15 basic surface patterns [LC87]. Once a surface pattern has been identified, for each voxel, a complete triangulation of the volume data will be obtained. There have been several attempts to utilise a localised Marching Cube algorithm for general computer graphics ap- plications. Shu et al. [SZK95] proposed an adaptive algo- rithm in 1995, which first applies the Marching Cubes al- gorithm to a sub-area of the volume. This sub-area was de- fined by a small fixed number of voxels in a grid. Later, Ko- rner et. al. [KBSS99] presented an approach where volu- metric data is locally transformed into a surface representa- tion for haptics. For the explicit local surface extraction, the Marching Cubes algorithm is employed on a 7x7x7 voxel c  The Eurographics Association 2008.