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ItemPhotoMeter: Easy-to-use MonoGraphoMetrics(Georgia Institute of Technology, 2004) Muller, Hendrik ; Rossignac, JarekMonoGraphoMetrics is the science of computing 3D measures from a single image. Several recent research activities have produced theoretical principles and practical tools for extracting 3D measures from uncalibrated photographs. These tools require that the user identifies configurations of edges, which are used to establish constraints or to identify planes in the scene. The process involved is often laborious and its application is limited to images where the required configurations of edges are visible. In contrast, the work presented here is limited to photographs taken with a calibrated camera, oriented horizontally, at a known height above the floor. Under these conditions, a single mouse click provides enough information to compute the 3D position of any point p in the coordinate system of the camera, provided that p and its projection f on the floor can be identified in the image. With this approach, a novice user of our PhotoMeter system can easily measure dimensions and positions of windows, doors, pieces of furniture, and even people with one or two mouse clicks per measurement. The paper describes the geometric computation of the measurements, the user interface, and a study of how errors in the height and horizontal orientation of the camera affect the measurements.
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ItemSupporting Personal Digital Storytelling: From People to Software(Georgia Institute of Technology, 2004) Landry, Brian Michael ; Guzdial, MarkEveryone has a personal story to tell. Often these stories are captured in the photos and videos we take to remember and share our experiences. Through a study of the Center for Digital Storytelling's workshops, we discovered telling personal stories using digital media captured during the experience requires more support than current software tools provide. We present a set of guidelines for supporting digital storytelling and strategies to implement each. We use the guidelines to assess the support a current software solution (Apple Computer's iLife series) provides. From our analysis, we identify supports needed for personal digital storytelling that are absent in tools today and provide suggestions for providing those missing supports.
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ItemOrthoMap: Homeomorphism-guaranteeing normal-projection map between surfaces(Georgia Institute of Technology, 2004) Chazal, Frederic ; Lieutier, Andre ; Rossignac, JarekConsider two (n—1)-dimensional manifolds, S and Sʹ in Rn. We say that they are projection-homeomorphic when the closest projection of each one onto the other is a homeomorphism. We give tight conditions under which S and Sʹ are projection-homeomorphic. These conditions involve the local feature size for S and for Sʹ and the Hausdorff distance between them. Our results hold for arbitrary n.
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ItemLoCoL: Encouraging Social Interaction and Exploration Through a Distributed, Multi-Media, Location-Based Mobile Game(Georgia Institute of Technology, 2004) Patel, Shwetak Naran ; Kientz, Julie A. ; Zagal, José PabloWe present a mobile collector card game called LoCoL, which uses a GPS-enabled mobile phone with a built-in camera to collect, trade, and create digital artifacts from landmarks and places that players have visited. When a player carrying the phone with LoCoL enabled passes within a half-mile radius of a landmark, he or she collects a "card" for that location. Players may then trade with other co-located players to try and build a large collection of unique cards from places they have been or places their acquaintances have been. Additionally, if they discover new, interesting landmarks, they may share it with others by taking a picture with their phone's built-in camera and submit the location to the game as a new card which others may collect. There is an element of competition in that players compete worldwide to collect the highest number of unique cards or the most number of approved cards submitted. We hope to encourage players to learn about and explore new, interesting locations and promote social interaction by allowing users to trade cards and initiate conversations as a result of the game.
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ItemA Probabilistic Approach to the Semantic Interpretation of Building Facades(Georgia Institute of Technology, 2004) Alegre, Fernando ; Dellaert, FrankWe present a probabilistic image-based approach to the semantic interpretation of building facades. We are motivated by the 4D Atlanta project at Georgia Tech, which aims to create a system that takes a collection of historical imagery of a city and infers a 3D model parameterized by time. Here it is necessary to recover, from historical imagery, metric and semantic information about buildings that might no longer exist or have undergone extensive change. Current approaches to automated 3D model reconstruction typically recover only geometry, and a systematic approach that allows hierarchical classification of structural elements is still largely missing. We extract metric and semantic information from images of facades, allowing us to decode the structural elements in them and their inter-relationships, thus providing access to highly structured descriptions of buildings. Our method is based on constructing a Bayesian generative model from stochastic context-free grammars that encode knowledge about facades. This model combines low-level segmentation and high-level hierarchical labelling so that the levels reinforce each other and produce a detailed hierarchical partition of the depicted facade into structural blocks. Markov chain Monte Carlo sampling is used to approximate the posterior over partitions given an image.
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ItemExpert Chording Text Entry on the Twiddler One-Handed Keyboard(Georgia Institute of Technology, 2004) Lyons, Kenton Michael ; Plaisted, Daniel ; Starner, ThadPreviously, we demonstrated that after 400 minutes of practice, ten novices averaged over 26 words per minute (wpm) for text entry on the Twiddler one-handed chording keyboard, outperforming the multi-tap mobile text entry standard. Here we present an extension of this study that examines expert chording performance. Five subjects continued the study and achieved an average rate of 47 wpm after approximately 25 hours of practice in varying conditions. One subject achieved a rate of 67 wpm, equivalent to the typing rate of the last author who has been a Twiddler user for ten years. We provide evidence that lack of visual feedback does not hinder expert typing speed and examine the potential use of multiple character chords (MCCs) to increase text entry speed. We demonstrate the effects of learning on various aspects of chording and analyze how subjects adopt a simultaneous or sequential method of pushing the individual keys during a chord.
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ItemMorphological Simplification(Georgia Institute of Technology, 2004) Williams, Jason Daniel ; Rossignac, JarekMorphological filters, such as closuer, opening, and their combinations, may be used for cleaning and analyzing images and shapes. We focus on the most popular special cases of these operators: the rounding R(S) and filleting F(S) of an arbitrary set S and the combinations R(F(S)) and F(R(S)). These operators may be obtained by combining growing and shrinking operators, which are Minkowski sums and differences with a ball of a given radius r. We define the mortar M(S) as F(S)-R(S). Note that the mortar occupies the thin cracks, protrusions, constrictions, and areas near the high-curvature portions of the boundary of S. Thus, we argue that confining the effect of shape simplification to the mortar has advantages over previously proposed tolerance zones and error metrics, which fail to differentiate between the irregular regions contained in the mortar and the regular (low-curvature) regions of S. We point out that R(F(S)) and F(R(S)) are suitable filters in this context, because their effects are confined to M(S) and leave the core R(S) and the anticore, which is the complement of F(S), unchanged. Furthermore, they tend to replace the high-curvature portions of the boundary of S with with regular portions where the radius of curvature exceeds r. Unfortunately, these operators have a bias, which may result in a large total volume of the symmetric difference between S and its simplified version S'. In order to minimize this volume, we propose to select the filter locally, for each connected component of the mortar. Thus, some portions of the mortar will be simplified using F(R(S)) and some using R(F(S)). This approach, which we call the Mason filter, can be used for the simplification of shapes regardless of their representation or dimensionality. We demonstrate its application to discrete two-dimensional binary sets (i.e. black and white images) and discuss implementation details.
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ItemVector Field Design on Surfaces(Georgia Institute of Technology, 2004) Zhang, Eugene ; Mischaikow, Konstantin Michael ; Turk, GregVector field design on surfaces is necessary for many graphics applications: example-based texture synthesis, non-photorealistic rendering, and fluid simulation. A vector field design system should allow a user to create a large variety of complex vector fields with relatively little effort. In this paper, we present a vector field design system for surfaces that allows the user to control the number of singularities in the vector field and their placement. Our system combines basis vector fields to make an initial vector field that meets the user's specifications. The initial vector field often contains unwanted singularities. Such singularities cannot always be eliminated, due to the Poincar'e-Hopf index theorem. To reduce the effect caused by these singularities, our system allows a user to move a singularity to a more favorable location or to cancel a pair of singularities. These operations provide topological guarantees for the vector field in that they only affect the user-specified singularities. Other editing operations are also provided so that the user may change the topological and geometric characteristics of the vector field. We demonstrate our vector field design system for several applications: example-based texture synthesis, painterly rendering of images, and pencil sketch illustrations of smooth surfaces.
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ItemTightening: Curvature-Limiting Morphological Simplification(Georgia Institute of Technology, 2004) Williams, Jason Daniel ; Rossignac, JarekGiven a planar set S of arbitrary topology and a radius r, we show how to construct an r -tightening of S, which is a set whose boundary has a radius of curvature everywhere greater than or equal to r and which only differs from S in a morphologically-defined tolerance zone we call the mortar. The mortar consists of the thin or highly curved parts of S, such as corners, gaps, and small connected components, while the boundary of a tightening consists of minimum-length loops through the mortar. Tightenings are defined independently of shape representation, and it may be possible to find them using a variety of algorithms. We describe how to approximately compute tightenings for sets represented as binary images using constrained, level-set curvature flow.
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ItemTetStreamer: Compressed Back-to-Front Transmission of Delaunay Tetrahedra Meshes(Georgia Institute of Technology, 2004) Bischoff, Urs ; Rossignac, JarekWe use the shorts tet and tri for tetrahedron and triangle. TetStreamer encodes a Delaunay tet mesh in a back-to-front visibility order and streams it from a server to a client (volumetric visualizer). During decompression, the server performs the viewdependent back-to-front sorting of the tets by identifying and deactivating one free tet at a time. A tet is free when all its back faces are on the sheet. The sheet is a tri mesh separating active and inactive tets. It is initialized with the back-facing boundary of the mesh. It is compressed using EdgeBreaker and transmitted first. It is maintained by both the server and the client and advanced towards the viewer passing one free tet at a time. The client receives a compressed bit stream indicating where to attach free tets to the sheet. It renders each free tet and updates the sheet by either flipping a concave edge, removing a concave valence-3 vertex, or inserting a new vertex to split a tri. TetStreamer compresses the connectivity of the whole tet mesh to an average of about 1.7 bits per tet. The footprint (in-core memory required by the client) needs only to hold the evolving sheet, which is a small fraction of the storage that would be required by the entire tetmesh. Hence, TetStreamer permits to receive, decompress, and visualize or process very large meshes on clients with a small in-core memory. Furthermore, it permits to use volumetric visualization techniques, which require that the mesh be processed in viewdependent back-to-front order, at no extra memory, performance or transmission cost.