Animation on the web: a survey <s> Compression & Preprocessing <s> Level-of-detail (LOD) representations are an important tool for realtime rendering of complex geometric environments. The previously introduced progressive mesh representation defines for an arbitrary triangle mesh a sequence of approximating meshes optimized for view-independent LOD. In this paper, we introduce a framework for selectively refining an arbitrary progressive mesh according to changing view parameters. We define efficient refinement criteria based on the view frustum, surface orientation, and screen-space geometric error, and develop a real-time algorithm for incrementally refining and coarsening the mesh according to these criteria. The algorithm exploits view coherence, supports frame rate regulation, and is found to require less than 15% of total frame time on a graphics workstation. Moreover, for continuous motions this work can be amortized over consecutive frames. In addition, smooth visual transitions (geomorphs) can be constructed between any two selectively refined meshes. A number of previous schemes create view-dependent LOD meshes for height fields (e.g. terrains) and parametric surfaces (e.g. NURBS). Our framework also performs well for these special cases. Notably, the absence of a rigid subdivision structure allows more accurate approximations than with existing schemes. We include results for these cases as well as for general meshes. CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation Display algorithms; I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling surfaces and object representations. Additional <s> BIB001 </s> Animation on the web: a survey <s> Compression & Preprocessing <s> Many applications in computer graphics require complex, highly detailed models. However, the level of detail actually necessary may vary considerably. To control processing time, it is often desirable to use approximations in place of excessively detailed models. We have developed a surface simplification algorithm which can rapidly produce high quality approximations of polygonal models. The algorithm uses iterative contractions of vertex pairs to simplify models and maintains surface error approximations using quadric matrices. By contracting arbitrary vertex pairs (not just edges), our algorithm is able to join unconnected regions of models. This can facilitate much better approximations, both visually and with respect to geometric error. In order to allow topological joining, our system also supports non-manifold surface models. CR Categories: I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling—surface and object representations <s> BIB002 </s> Animation on the web: a survey <s> Compression & Preprocessing <s> Lossless transmission of 3D meshes is a very challenging and timely problem for many applications, ranging from collaborative design to engineering. Additionally, frequent delays in transmissions call for progressive transmission in order for the end user to receive useful successive refinements of the final mesh. In this paper, we present a novel, fully progressive encoding approach for lossless transmission of triangle meshes with a very fine granularity. A new valence-driven decimating conquest, combined with patch tiling and an original strategic retriangulation is used to maintain the regularity of valence. We demonstrate that this technique leads to good mesh quality, near-optimal connectivity encoding, and therefore a good rate-distortion ratio throughout the transmission. We also improve upon previous lossless geometry encoding by decorrelating the normal and tangential components of the surface. For typical meshes, our method compresses connectivity down to less than 3.7 bits per vertex, 40% better in average than the best methods previously reported [5, 18]; we further reduce the usual geometry bit rates by 20% in average by exploiting the smoothness of meshes. Concretely, our technique can reduce an ascii VRML 3D model down to 1.7% of its size for a 10-bit quantization (2.3% for a 12-bit quantization) while providing a very progressive reconstruction. <s> BIB003 </s> Animation on the web: a survey <s> Compression & Preprocessing <s> Surface geometry is often modeled with irregular triangle meshes. The process of remeshing refers to approximating such geometry using a mesh with (semi)-regular connectivity, which has advantages for many graphics applications. However, current techniques for remeshing arbitrary surfaces create only semi-regular meshes. The original mesh is typically decomposed into a set of disk-like charts, onto which the geometry is parametrized and sampled. In this paper, we propose to remesh an arbitrary surface onto a completely regular structure we call a geometry image. It captures geometry as a simple 2D array of quantized points. Surface signals like normals and colors are stored in similar 2D arrays using the same implicit surface parametrization --- texture coordinates are absent. To create a geometry image, we cut an arbitrary mesh along a network of edge paths, and parametrize the resulting single chart onto a square. Geometry images can be encoded using traditional image compression algorithms, such as wavelet-based coders. <s> BIB004 </s> Animation on the web: a survey <s> Compression & Preprocessing <s> We present the "Geometry Video," a new data structure to encode animated meshes. Being able to encode animated meshes in a generic source-independent format allows people to share experiences. Changing the viewpoint allows more interaction than the fixed view supported by 2D video. Geometry videos are based on the "Geometry Image" mesh representation introduced by Gu et al. 4. Our novel data structure provides a way to treat an animated mesh as a video sequence (i.e., 3D image) and is well suited for network streaming. This representation also offers the possibility of applying and adapting existing mature video processing and compression techniques (such as MPEG encoding) to animated meshes. This paper describes an algorithm to generate geometry videos from animated meshes.The main insight of this paper, is that Geometry Videos re-sample and re-organize the geometry information, in such a way, that it becomes very compressible. They provide a unified and intuitive method for level-of-detail control, both in terms of mesh resolution (by scaling the two spatial dimensions) and of frame rate (by scaling the temporal dimension). Geometry Videos have a very uniform and regular structure. Their resource and computational requirements can be calculated exactly, hence making them also suitable for applications requiring level of service guarantees. <s> BIB005 </s> Animation on the web: a survey <s> Compression & Preprocessing <s> A view-dependent graphics streaming scheme is proposed in this work that facilitates interactive streaming and browsing of three-dimensional (3-D) graphics models. First, a 3-D model is split into several partitions. Second, each partition is simplified and coded independently. Finally, the compressed data is sent in order of relevance to the user's requests to maximize visual quality. Specifically, the server can transmit visible parts in detail, while cutting out invisible parts. Experimental results demonstrate that the proposed algorithm reduces the required transmission bandwidth, and provides an acceptable visual quality even at low bit rates. <s> BIB006 </s> Animation on the web: a survey <s> Compression & Preprocessing <s> 3D triangle meshes are extremely used to model discrete surfaces, and almost always represented with two tables: one for geometry and another for connectivity. While the raw size of a triangle mesh is of around 200 bits per vertex, by coding cleverly (and separately) those two distinct kinds of information it is possible to achieve compression ratios of 15:1 or more. Different techniques must be used depending on whether single-rate vs. progressive bitstreams are sought; and, in the latter case, on whether or not hierarchically nested meshes are desirable during reconstruction. <s> BIB007 </s> Animation on the web: a survey <s> Compression & Preprocessing <s> 3D animations have been widely used in the movie and gaming industries. However, the huge storage requirements of dynamic mesh data make it difficult for a number of applications such as rendering, transmitting over a network, etc.This study proposes a multiresolution representation for 3D animation. The results show that the coarse animation appears by using only 10% of the original faces. More detailed animation appears by using 80% of original faces, but only requires 3% of original storage space. Consequently, this approach enables a continuous level of detail for dynamic 3D mesh sequences. <s> BIB008 </s> Animation on the web: a survey <s> Compression & Preprocessing <s> Abstract In recent years, 3D graphics has become an increasingly important part of the multimedia web experience. Following on from the advent of the X3D standard and the definition of a declarative approach to presenting 3D graphics on the web, the rise of WebGL has allowed lower level access to graphics hardware of ever increasing power. In parallel, remote rendering techniques permit streaming of high-quality 3D graphics onto a wide range of devices, and recent years have also seen much research on methods of content delivery for web-based 3D applications. All this development is reflected in the increasing number of application fields for the 3D web. In this paper, we reflect this activity by presenting the first survey of the state of the art in the field. We review every major approach to produce real-time 3D graphics rendering in the browser, briefly summarise the approaches for remote rendering of 3D graphics, before surveying complementary research on data compression methods, and notable application fields. We conclude by assessing the impact and popularity of the 3D web, reviewing the past and looking to the future. <s> BIB009
The large amount of data which needs to transmitted for animation thus benefits from some level of compression and preprocessing, in order to reduce the time taken to transfer the data. However, as pointed out by BIB009 , the balance between compression and speed is delicate, as complex compression can take time to decompress within a browser context, which is required to use interpreted JavaScript to do the work (and, thus, is slower). The balance between compression and bandwidth has been demonstrated effectively by  . Every mesh and its animation data is defined by: Geometry (Vertex Positions), Connectivity (graph of triangles) BIB007 BIB003 BIB008 and texture/color data. On a broad scale, Compression can be divided into two groups: Single Rate Compression: encodes and decodes the 3D object as a whole, thus we see the entire 3D object only after the data is decoded. These algorithms work by removing the redundancy in the dataset, while making no assumptions about its complexity, regularity or uniformity. Although these methods can achieve really good compression ratios, they are unsuitable for the network  . For readers interested, we direct them to these comprehensive survey papers as a starting point  BIB007  Progressive Compression: Progressive compression of 3D meshes uses the concept of refinement over a period of time. The idea is to transmit the crude approximation first, then predict intermediate vertices and either transmit the residues for the prediction or generate refinement of the mesh progressively. During decoding the connectivity of geometry is reconstructed incrementally from the transmission stream. The main advantage here is the minimal wait time for the user as intermediate states are transmitted through the network.  proposed progressive meshes (PM) in his seminal paper: a progressive mesh is obtained from a simplified base mesh and a series of vertex splits (vsplits), which are used to refine the base mesh into a more refined and detailed mesh. Hoppe et al. took this further and developed view-dependent progressive meshes (VPM) where features contributing to the visible part is given priority for transmission. BIB001 BIB006 . Garland et al. proposed BIB002 a method based on simplifying the vertex pair in the mesh iteratively, which was accurate and had a very low computation time. The simplified edge sequence is determined by the quadric error metrics (QEM) -a quadric measure which is a matrix that represents the sum of the squared distances from the vertex to the planes of neighboring triangles, is associated with each vertex. Geometry videos BIB005 ] offer a different approach, based on the geometry images of BIB004 . The mesh is first parameterized, then re-sampled over a regular grid in space. The result is a 2D image with three channels, for x, y and z coordinates. The mesh geometry is stored or transmitted simply as an image stream, which can be compressed using existing video compression methods.