A framework for working with digitized cultural heritage artefacts

In this paper, we present our work in designing, implementing, and evaluating a set of 3D interactive spatial measurement tools in the context of Cultural Heritage Toolbox (CH Toolbox), a framework for computer-aided cultural heritage research. Our application utilizes a bi-manual, spaceball and mouse driven user interface to help the user manage visualized 3D models digitized from real artifacts. We have developed a virtual radius estimator, useful for analyzing incomplete pieces of radial artifacts, and a virtual tape measure, useful in measurement of geodesic distances between two points on the surface of an artifact. We tested the tools on the special case of pottery analysis

Normal map : High poly -mallin pinnanmuotojen siirtäminen low poly -mallille

Opinnäytetyö käsittelee 3D-mallien tekstuureita ja sitä, kuinka niillä voidaan luoda illuusio tarkemmin mallinnetusta kappaleesta. Normal map -tekstuurit, joihin työ erityisesti keskittyy, mahdollistavat yksityiskohtaisen mallin pinnanmuotojen näennäisen siirtämisen yksinkertaisemmalle kappaleelle. Opinnäytetyön tavoite on myös kartoittaa yleisesti reaaliaikaiseen renderöimiseen soveltuvia malleja ja tekstuureita. Aihetta lähestytään normaalikarttojen ja niiden ominaisuuksien kautta. Opinnäytetyö koostuu tekstuureihin, erityisesti pelialalla käytettyihin, ja normaalikarttoihin tutustumisesta ja sekä kolmen esimerkkityön yksityiskohtaisesta projektikuvauksesta. Esimerkkityöt esittelevät kolme erilaista tapaa luoda normal map Autodesk 3Ds Max -ohjelmalla luodulle mallille. Opinnäytetyössä käsitellään myös normal mapin luomista yleisemmällä tasolla. Normaalikartat ovat tehokas menetelmä luoda yksityiskohtaisia malleja tekemättä niistä liian raskaita nopealle renderöimiselle. Ennen normaalikarttoja käytettiin bump mapping -tekniikkaa, joka jää menetelmiä verratessa normal mapien taakse tarkkuudessaan ja realistisuudessaan. Menetelmän tekee hyödylliseksi se, että se ei tee 3D-scenestä tai objektista niin raskasta kuin mitä oikea korkearesoluutioinen kappale olisi. Normaalikartta pyrkii säilyttämään tarkan mallin yksityiskohdat siirtämättä high poly -mallien heikkouksia, kuten pitkiä renderöimisaikoja ja scenen raskautta low poly -malliin. Metodi on erityisen hyödyllinen reaaliaikaisessa mediassa ja on laajasti käytössä pelialalla.The thesis focuses on different textures used on a 3D model and how they can create the illusion of a more detailed surface on a simpler mesh. The main subject consisted of normal maps and how they enable the assigning of a more complex model's surface normals for a simpler one. The objective was to examine different ways of creating normal maps and to understand the demands of realtime rendering towards textures and models. This study includes illustration of the background of different textures used in the 3D field, especially those used in medium that require realtime rendering. It includes detailed description of three different ways to create a normal map for use on a model created in Autodesk 3Ds Max and information about creating a normal map in general. Normal mapping is an efficient way of creating light but detailed models. Prior to normal mapping, bump mapping was the method used to accomplish a similar result. Comparison of these approaches shows the advantage of normal maps over bump maps. The benefit of using normal mapping is to obtain the appearance of a high poly model without having to deal with slow processing and long rendering times. Normal maps are commonly utilised in real-time media and these days are essential for video games

Multilevel Solvers for Unstructured Surface Meshes

Parameterization of unstructured surface meshes is of fundamental importance in many applications of digital geometry processing. Such parameterization approaches give rise to large and exceedingly ill-conditioned systems which are difficult or impossible to solve without the use of sophisticated multilevel preconditioning strategies. Since the underlying meshes are very fine to begin with, such multilevel preconditioners require mesh coarsening to build an appropriate hierarchy. In this paper we consider several strategies for the construction of hierarchies using ideas from mesh simplification algorithms used in the computer graphics literature. We introduce two novel hierarchy construction schemes and demonstrate their superior performance when used in conjunction with a multigrid preconditioner

Exact Geosedics and Shortest Paths on Polyhedral Surface

We present two algorithms for computing distances along a non-convex polyhedral surface. The first algorithm computes exact minimal-geodesic distances and the second algorithm combines these distances to compute exact shortest-path distances along the surface. Both algorithms have been extended to compute the exact minimalgeodesic paths and shortest paths. These algorithms have been implemented and validated on surfaces for which the correct solutions are known, in order to verify the accuracy and to measure the run-time performance, which is cubic or less for each algorithm. The exact-distance computations carried out by these algorithms are feasible for large-scale surfaces containing tens of thousands of vertices, and are a necessary component of near-isometric surface flattening methods that accurately transform curved manifolds into flat representations.National Institute for Biomedical Imaging and Bioengineering (R01 EB001550

Surface Edge Explorer (SEE): Planning Next Best Views Directly from 3D Observations

Surveying 3D scenes is a common task in robotics. Systems can do so autonomously by iteratively obtaining measurements. This process of planning observations to improve the model of a scene is called Next Best View (NBV) planning. NBV planning approaches often use either volumetric (e.g., voxel grids) or surface (e.g., triangulated meshes) representations. Volumetric approaches generalise well between scenes as they do not depend on surface geometry but do not scale to high-resolution models of large scenes. Surface representations can obtain high-resolution models at any scale but often require tuning of unintuitive parameters or multiple survey stages. This paper presents a scene-model-free NBV planning approach with a density representation. The Surface Edge Explorer (SEE) uses the density of current measurements to detect and explore observed surface boundaries. This approach is shown experimentally to provide better surface coverage in lower computation time than the evaluated state-of-the-art volumetric approaches while moving equivalent distances

Signal-Specialized Parameterization

To reduce memory requirements for texture mapping a model, we build a surface parametrization specialized to its signal (such as color or normal). Intuitively, we want to allocate more texture samples in regions with greater signal detail. Our approach is to minimize signal approximation error --- the difference between the original surface signal and its reconstruction from the sampled texture. Specifically, our signal-stretch parametrization metric is derived from a Taylor expansion of signal error. For fast evaluation, this metric is pre-integrated over the surface as a metric tensor. We minimize this nonlinear metric using a novel coarse-to-fine hierarchical solver, further accelerated with a fine-to-coarse propagation of the integrated metric tensor. Use of metric tensors permits anisotropic squashing of the parametrization along directions of low signal gradient. Texture area can often be reduced by a factor of 4 for a desired signal accuracy compared to non-specialized parametrizations.Engineering and Applied Science