Patrick Marais

Terrain sketching

Procedural methods for terrain synthesis are capable of creating realistic depictions of heightfield terrains with little user intervention. However, users often do wish to intervene in controlling the placement and shape of landforms, but without sacrificing realism. In this paper, we present a sketching interface to procedural terrain generation. This system enables users to draw the silhouette, spine and bounding curves of both extruding (hills and mountains) and embedding landforms (river courses and canyons). Terrain is interactively generated to match the sketched constraints using multiresolution surface deformation. In addition, the wavelet noise characteristics of silhouette strokes are propagated to the surrounding terrain. With terrain sketching users can interactively create or modify landscapes incorporating varied and complex land-forms.

Animation space: A truly linear framework for character animation

Skeletal subspace deformation (SSD), a simple method of character animation used in many applications, has several shortcomings; the best-known being that joints tend to collapse when bent. We present animation space, a generalization of SSD that greatly reduces these effects and effectively eliminates them for joints that do not have an unusually large range of motion.While other, more expensive generalizations exist, ours is unique in expressing the animation process as a simple linear transformation of the input coordinates. We show that linearity can be used to derive a measure of average distance (across the space of poses), and apply this to improving parametrizations.Linearity also makes it possible to fit a model to a set of examples using least-squares methods. The extra generality in animation space allows for a good fit to realistic data, and overfitting can be controlled to allow fitted models to generalize to new poses. Despite the extra vertex attributes, it is possible to render these animation-space models in hardware with no loss of performance relative to SSD.

A case study in the gamification of a university-level games development course

Gamification is the application of game mechanics and player incentives to non-game environments. When designed correctly, gamification has been found to increase engagement and encourage targeted behaviours among users. This paper presents the gamification of a university course in Computer Games Development using an online learning management tool, including how this might generalize to other courses. Our goal with gamification was to improve lecture attendance, content understanding, problem solving skills and general engagement. The success of this intervention was measured using course marks, lecturer evaluations, lecture attendance, and a questionnaire; all with strongly positive results. However, this must be balanced against the costs, both monetary and time, required to successfully implement gamification.

Compression of dense and regular point clouds

We present a simple technique for single-rate compression of point clouds sampled from a surface, based on a spanning tree of the points. Unlike previous methods, we predict future vertices using both a linear predictor, which uses the previous edge as a predictor for the current edge, and lateral predictors that rotate the previous edge 90° left or right about an estimated normal.By careful construction of the spanning tree and choice of prediction rules, our method improves upon existing compression rates when applied to regularly sampled point sets, such as those produced by laser range scanning or uniform tesselation of higher-order surfaces. For less regular sets of points, the compression rate is still generally within 1.5 bits per point of other compression algorithms.

Three-dimensional surface deformation-based shape analysis of hippocampus and caudate nucleus in children with fetal alcohol spectrum disorders.

Surface deformation‐based analysis was used to assess local shape variations in the hippocampi and caudate nuclei of children with fetal alcohol spectrum disorders. High‐resolution structural magnetic resonance imaging images were acquired for 31 children (19 controls and 12 children diagnosed with fetal alcohol syndrome/partial FAS). Hippocampi and caudate nuclei were manually segmented, and surface meshes were reconstructed. An iterative closest point algorithm was used to register the template of one control subject to all other shapes in order to capture the true geometry of the shape with a fixed number of landmark points. A point distribution model was used to quantify the shape variations in terms of a change in co‐ordinate positions. Using the localized Hotelling T2 method, regions of significant shape variations between the control and exposed subjects were identified and mapped onto the mean shapes. Binary masks of hippocampi and caudate nuclei were generated from the segmented volumes of each brain. These were used to compute the volumes and for further statistical analysis. The Mann–Whitney test was performed to predict volume differences between the groups. Although the exposed and control subjects did not differ significantly in their volumes, the shape analysis showed the hippocampus to be more deformed at the head and tail regions in the alcohol‐exposed children. Between‐group differences in caudate nucleus morphology were dispersed across the tail and head regions. Correlation analysis showed associations between the degree of compression and the level of alcohol exposure. These findings demonstrate that shape analysis using three‐dimensional surface measures is sensitive to fetal alcohol exposure and provides additional information than volumetric measures alone. Hum Brain Mapp 35:659–672, 2014.

Visualising Cerebral Asymmetry

We describe techniques for visualising and measuring the asymmetry of the cerebral hemispheres based on MRI scans. These techniques improve on previous approaches in two ways: firstly, measurements are not limited to voxel discretisation scales; secondly, symmetry measurements are inherently 3D. This avoids the errors in slice-based measurements arising from shape distortions introduced by misalignment between the head and MRI machine.

A stateless client for progressive view-dependent transmission

We present a framework for real-time view-dependent refinement, and adapt it to the task of browsing large model repositories on the Internet. We introduce a novel hierarchical representation of atomic operations based on a graph structure, and provide a correspondence between the nodes of this hierarchy and a spatial representation of these operations, called visibility spheres. Selective refinement is achieved by performing a breadth first search on the graph. We show that the graph representation allows for significant space savings. The framework presented makes options available for performance tailoring. By efficient traversal of the graph structure an ordered list of refinements can be generated which are progressive and evenly distributed over the refinement area. This list can easily be truncated to comply with polygon limitations indicated by a client. CR Categories: I.3.2 [Computer Graphics]: Picture/Image Generation—Display Algorithms; I.3.5 [Computer Graphics]: Computational Geometry and Object Modelling—Surfaces and Object Representations

Parallel, Realistic and Controllable Terrain Synthesis

The challenge in terrain synthesis for virtual environments is to provide a combination of precise user control over landscape form, with interactive response and visually realistic results.

Enhanced Texture-Based Terrain Synthesis on Graphics Hardware

Curvilinear features extracted from a 2D user‐sketched feature map have been used successfully to constraint a patch‐based texture synthesis of real landscapes. This map‐based user interface does not give fine control over the height profile of the generated terrain. We propose a new texture‐based terrain synthesis framework controllable by a terrain sketching interface. We enhance the realism of the generated landscapes by using a novel patch merging method that reduces boundary artefacts caused by overlapping terrain patches. A more constrained synthesis process is used to produce landscapes that better match user requirements. The high computational cost of texture synthesis is reduced with a parallel implementation on graphics hardware. Our GPU‐accelerated solution provides a significant speedup depending on the size of the example terrain. We show experimentally that our framework is more successful in generating realistic landscapes than current example‐based terrain synthesis methods. We conclude that texture‐based terrain synthesis combined with sketching provides an excellent solution to the user control and realism challenges of virtual landscape generation.

Compression of Dense and Regular Point Clouds

We present a simple technique for single‐rate compression of point clouds sampled from a surface, based on a spanning tree of the points. Unlike previous methods, we predict future vertices using both a linear predictor, which uses the previous edge as a predictor for the current edge, and lateral predictors that rotate the previous edge 90°left or right about an estimated normal.