First Person Indoor/Outdoor Augmented Reality Application: ARQuake Abstract: This paper presents a first person outdoor/indoor augmented reality application ARQuake that we have developed. ARQuake is an extension of the desktop game Quake, and as such we are investigating how to convert a desktop first person application into an outdoor/indoor mobile augmented reality application. We present an architecture for a low cost, moderately accurate six degrees of freedom tracking system based on GPS, digital compass, and fiducial vision-based tracking. Usability issues such as monster selection, colour, input devices, and multi-person collaboration are discussed. Many current applications place the user in a first-person perspective view of a virtual world [1] , such as games, architectural design viewers [2] , geographic information systems and medical applications [3, 4] . In this paper, we describe a project to move these forms of applications outdoors, displaying their relevant information by augmenting reality. In particular we consider the game Quake (idSoftware). As with other researchers [5] , we wish to place these applications in a spatial context with the physical world, which we achieve by employing our wearable computer system Tinmith [6] [7] [8] . Tinmith is a context-aware wearable computer system, allowing applications to sense the position of the user's body and the orientation of the user's head. The technique we are developing will genuinely take computers out of the laboratory and into the field, with geographically-aware applications designed to interact with users in the physical world, not just in the confines of the computer's artificial reality. The key to this exciting practical technology is augmented reality (AR). Users view overlaid computer-generated information by means of see-through head-mounted displays. Unlike virtual reality, where the computer generates the entire user environment, augmented reality places the computer in a relatively unobtrusive, assistive role.. In the ARQuake application, a simplified representation of the physical world gaming location is modelled as a Quake 3D graphical model. The augmented reality information (monsters, weapons, objects of interest) is displayed in spatial context with the physical world. The Quake model of the physical world (walls, ceiling, floors) is not shown to the user: the see-through display allows the user to see the actual walls, ceilings and floors which ARQuake need only model internally. Coincidence of the actual structures and virtual structures is key to the investigation; the AR application models the existing physical outdoor structures, and so omission of their rendered image from the display becomes in effect one of our rendering techniques. This paper reports on an ongoing research project -ARQuake, an outdoor/indoor augmented reality first-person application. Although the implementation has not been completed, many interesting results have been found, in particular user interface issues for AR outdoor/indoor augmented reality games; an architecture for low cost, moderately accurate indoor/outdoor 6DOF tracking; and implementation issues for converting a desktop application into an AR application.. The current ARQuake game is running on our wearable computer platform with the 6DOF GPS/compass tracking system. The interaction of the game was operating within the accuracy of this tracking system. We have modelled an outdoor section of our campus and interior of the WCL. The graphics of the game are running at approximately 30 frames per second, with GPS updates once per second and compass updates at 15 times per second.. The results of our research to this point in the implementation, include the design and implementation of a user interface for an augmented reality application, and proposed some guidelines. Specifically, identified by informal experimental evidence, a set of colours that take into account different lighting and background colours for outdoors use. We successfully mapped the keyboard and mouse interactions of the ARQuake application to head/body movements and a simple two-button input device. A simple user interface layout was incorporated into the ARQuake application. The game is quite playable in this configuration, and we are continuing to investigate how to overcome difficulties with registration errors when indoors and close to buildings.. We proposed and described a low cost moderately accurate indoor/outdoor 6DOF tracking system, by a novel combination of optical tracking and GPS/compass tracking to provide an absolute tracking system.. The solution is not restricted to overcoming registration problems, but it does provide a general tracking solution. Fiducial markers are placed at the corners of buildings to provide more accurate positioning information for ARQuake. When a fiducial marker comes into view of a head mounted camera, this more accurate tracking information is used instead of the GPS/ compass data. The vision based tracking is not fully functional, and we are continuing to investigate and develop this solution.. Aside from the specific technical achievements of our work to date, it is perhaps most important to point out that our work can serve as proof that augmented reality is readily achievable with inexpensive, off-the-shelf software. The translation of the application set from the desktop to incorporate the physical world brings closer the possibility of truly ubiquitous computing. There are two basic styles of tracking: absolute and relative. Furthermore, machine learning can train a system to recognise locations in a building or outdoors. Golding and Lesh use an array of sensors: accelerometers, magnetometers, temperature and light to track a user in a set of known locations [10] . Aoki, Schiele and Pentland [11] use a camera to train the system to recognize the user's location and approaching trajectory. These systems can determine its present room, and whether it is entering or leaving that room.. Previous research has established that outdoor tracking with inexpensive differential GPS and commercial grade magnetic compasses are inaccurate for augmented reality applications [12] . Traditional hybrid approaches combine a number of different systems such as inertial, optical, electro-magnetic and GPS. In this paper, we present our hybrid approach of combining vision-based optical tracking with GPS and a magnetic compass.. A number of researchers are investigating fiducial vision-based tracking [3, 13] . We based our optical tracking system on the fiducial marker tracking system ARToolKit developed by Kato and Billinghurst [14] . The ARToolKit is a set of computer vision tracking libraries that can be used to calculate camera position and orientation relative to physical markers in real time. ARToolKit features include the use of a single camera for position/orientation tracking, fiducial tracking from simple black squares, pattern matching software that allows any marker patterns to be used, calibration code for video and optical see-through applications, and sufficiently fast performance for real-time augmented reality applications.. The fiducial markers are known-sized squares with high contrast patterns in their centres. Figure 1 shows an example marker. The ARToolKit determines the relative distances and orientation of the marker from the camera. In addition, the ARToolKit incorporates a calibration application to determine the placement of the camera relative to the user's line of sight; thus the ARToolKit can determine proper placement of graphical objects for AR applications.

O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Constructing Two-layered Freight Traffic Network Model from Truck Probe Data The road network in the Keihanshin area (the second most populated urban region in Japan encompassing the metropolitan areas of the cities of Osaka in Osaka prefecture, Kobe in Hyōgo Prefecture, and Kyoto in Kyoto prefecture) is modeled as two layers from the viewpoint of the frequency of use of roads by freight vehicles. This model was derived ,tested and validated from the probe car data of 300 trucks operated by 21 freight companies in the Keihanshin area. The two layers are called high-frequency-network and low-frequency-network layers. Characteristics, such as the density of probe data, average driving time, and speed of both network layers, were estimated. This analysis revealed that trucks spend a duration about 6 times longer on the high-frequency network even though it is 1/4 the size of the low-frequency network. The instantaneous velocity histograms indicated a significant difference in speeds between the two network layers of 25.03 km/h in the high-frequency layer and 16.87 km/h in the low-frequency layer. Service-level evaluations, reliability analysis, and route-selection modeling should become easier to deal with in the future by introducing these layered networks. We tried to identify frequently used road networks, or the distribution of probe data in other words, traveled by freight vehicles from truck probe data. This was done through an experiment involving 300 trucks from 21 freight companies in the Keihanshin area of Japan. If we can understand frequently used networks traveled by freight vehicles, we can study the behavior of freight vehicles that choose routes more efficiently than that in studies without knowledge on frequently used networks. There have been several papers that have discussed the spatial coverage problem and the construction of driver route-choice models based on probe car data. However, very few studies have been done on the spatial distribution of probe cars. To estimate the density of probe data, the target area in the Keihanshin area was divided into small cells of 20 by 20 m and the probe data that fell into these cells were counted. This count was defined as probe density. We found that the distribution in the number of cells with respect to the minimum probe density followed that of the sum of two different exponentially decaying functions. We assumed that the road network could be separated into two distinctive layers according to the frequency of the use of road links acquired from the probe data. These layers reflected the actual truck traffic flow and were generated from the viewpoint of the frequency of truck probe car traffic. Two layers, i.e., high-frequency-network and low-frequency-network layers, were generated based on these distributions. This assumption was tested, validated and we propose a formulation of the model. This model should contribute to useful evaluations of road-network-service levels and reliability. Route-selection models should be able to be formulated based on the high-frequency-network layer in the future. We presented results that we obtained by analyzing truck probe data. The six main findings were: 1) The road network could be modeled as a two layered network, and both layers could be adaptively constructed according to the frequency of road use, which was calculated with probe data. 2) Trucks in the Keihanshin area spent about 6 times longer on the high frequency network even though it was 1/4 the size of the low frequency network. It should be emphasized that 87% (model) or 78% (actual) of the time spent by trucks was in the high frequency network in the Osaka area. Thus, improving the reliability, efficiency, and safety of the high frequency network deserves a higher priority.. 3) The instantaneous velocity histograms did reveal a significant difference between the two layers as one of their main characteristics, e.g., the mean value was 16.87 km/h in the low frequency network and 25.03 km/h in the high frequency network. 4) There was a saddle point in the profile of the number of stop points for trucks. The saddle point ranged from 200 to 600 sec. This means that trucks" inherent stops ranged from about 600 seconds. 5) Evaluation of services, analysis of reliability and modeling of route selection should become easier to deal with and become simpler and more effective based on this two-layered network. 6) The concept of the layered network model may also be applied to traffic involving passenger vehicles.

O O B I B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O


Political expression and action on social media: Exploring the relationship between lower- and higher-threshold political activities among Twitter users in Italy Scholars and commentators have debated whether lower-threshold forms of political engagement on social media should be treated as being conducive to higher-threshold modes of political participation or a diversion from them. Drawing on an original survey of a representative sample of Italians who discussed the 2013 election on Twitter, we demonstrate that the more respondents acquire political information via social media and express themselves politically on these platforms, the more they are likely to contact politicians via e-mail, campaign for parties and candidates using social media, and attend offline events to which they were invited online. These results suggest that lower-threshold forms of political engagement on social media do not distract from higher-threshold activities, but are strongly associated with them. Social media are an increasingly populated forum in which voters interact with politicians and express their views about public affairs. Some scholars emphasize the participatory potential of the "information exuberance" (Chadwick, 2009 ) that emerges on these platforms, whereas others dismiss it as "slacktivism", an irrelevant distraction from effective collective action. As Gladwell (2010, p. 49 ) put it, social media "makes it easier for activists to express themselves, and harder for that expression to have any impact." We evaluate these competing claims by testing whether lowerthreshold forms of political engagement -accessing political information and expressing political views on social media -are associated with higher-threshold modes of political action on and beyond the web. Alternatively, as the slacktivism hypothesis suggests, acquiring information and expressing oneself politically on social media may delude individuals into thinking that they are engaged whereas in reality they are not, thus subtracting valuable time and effort from more demanding political activities. We test hypotheses related to these relationships with data from a unique online survey of a representative sample of Italians who discussed the 2013 general election campaign on Twitter. We assess whether respondents' use of social media for political information and expression -which are relatively easy ways to engage politically on these platforms -are associated with increased probabilities that they participate in more demanding activities such as emailing politicians, campaigning for them on social media, and attending offline political events after receiving an online invitation. In contrast with the most critical views of new forms of political information and expression afforded by social media, we find positive and statistically significant associations between the lower-threshold and higher-threshold activities we tested. We also find that individuals who intensely use social media to both publish and read political messages, as well as those who post high amounts of messages while reading fewer, are the most likely to also engage in higher-threshold political action. These findings suggest that, by enabling individuals to express their political views and to learn political news, social media can meaningfully contribute to political action. The health of democracies depends, among other things, on citizens' political participation. Our findings suggest that political information and self-expression on social media contribute to these qualities rather than endangering them. We evaluated whether lower-threshold forms of engagement enabled by social media are a form of "slacktivist" chatter unrelated to, and distracting from, other forms of higher-threshold involvement, and found that this does not seem to be the case, at least in our population of Twitter users who discussed the Italian 2013 election. On the contrary, higher levels of online political information and expression are associated with higher probabilities that individuals also email politicians, use social media to encourage others to vote for a party or candidate, and attend events after receiving an online invitation. We interpret these results as a strong encouragement to treat citizens' expression on social media as a substantial and potentially consequential mode of political engagement rather than a diversion from it. This conclusion is reinforced by our findings that participation in higher-threshold activities was greater in those groups that were either very active as publishers of political messages or intensely involved in both the production and consumption of political content on the web 2.0. Digital citizenship is thus enhanced when individuals use social media in "write" and "read-write" modes rather than when they resort to "read-only" approaches whereby they expose themselves to political messages without contributing much to exchanges of ideas and information.. The evidence presented here suggests various lines of future inquiry. First, the content of citizens' political discussions and interactions on social media should be studied to determine whether observable acts of self-expression on these platforms corroborate the evidence from the self-reports that we presented. Second, comparative research is needed to assess the role of institutions and context in shaping political engagement on social media and their implications.. Thirdly, more work is needed to disentangle the causal patterns and mechanisms behind the associations that we found. Fourth, we need to study the connections between citizens' political activities on and off the internet in a more systematic way, possibly combining qualitative and quantitative methods of inquiry, in order to gauge the extent to which digital media are changing the context of important democratic endeavors as well as affecting specific modes of citizen information and participation. Finally, to the extent that social media use is increasing in all societies where it has been measured and that Twitter is only one of several such platforms, it is crucial to investigate whether our conclusions can be generalized to broader populations than the one we studied here-in which case the implications of social media for political engagement may turn out to be even more profound than we have shown here. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 1 Gender -2 Age .11** - Our findings suggest that activities enabled by social media generally thought of as lower-threshold forms of political engagement are positively associated with higher-threshold political activities that occur both online and offline. We tested two specific forms of lower-threshold engagementgetting political information and expressing oneself politically -and found support for both the first and, especially, the second type of activity as potential precursors to more demanding forms of participation. Thus, communicating about politics on social media is likely to be accompanied by more demanding action, whether it is contacting politicians, campaigning for them, or attending events. Our findings concerning political information confirm earlier studies of the implications of political news acquired via mass and digital media, and our findings concerning political expression echo those of more recent research suggesting that social media and other discursive online environments contribute a great deal to citizens' participatory repertoires. They are also consistent with the argument that the very act of "being political" on social media -that is, sharing political content and opinions -facilitates other forms of political action in two possible ways. First, engaging in political discussions on social media may reveal to a given individual his or her own political preferences (of which s/he might not previously have been entirely aware), a possibility that is not unrealistic given the pervasiveness of social media in users' everyday lives and the ease with which individuals can be drawn into various types of conversations, including political ones, on these platforms. Secondly, being part of these political exchanges may increase users' beliefs in their own internal efficacy by demonstrating that they can indeed participate in the political process and this may give them the confidence needed to try other forms of political participation.. Higher-threshold online activism is most common among those individuals who use social media intensively to post political messages as well as those who, in addition to publishing high amounts of political content, are also heavily involved in reading other people's comments and viewpoints. By contrast, respondents who prefer to read rather than to post were substantially less likely to be active in other domains. These findings reinforce the idea that online political expression and engagement strengthen one another rather than being alternatives. Similar outcomes can be observed when frequent expression is matched with sustained exposure to other individuals' political postings, suggesting that inward-oriented flows of political communication enabled by social media are associated with higher-threshold forms of participation when they are matched with outward-oriented ones.. It is important to recognize that our data do not allow us to investigate the direction of the causal patterns underlying the associations that we observed. First, establishing causality would require the analysis of longitudinal or experimental rather than cross-sectional survey data.. Secondly, we studied a specific population of individuals who posted at least one election-related message, and we cannot determine whether our findings can be generalized to other populations.. Endogeneity is inevitable in our models and our data do not allow us to establish the direction of the causal relationships behind the associations we have identified; indeed, it is for this reason that our hypotheses specifically predict associations, as opposed to causal effects. Moreover, as with any single-country study, our findings may also be affected by some specific systemic features of Italian politics and technology, discussed in section 4. However, we have no a priori reason to believe that the patterns we have identified among Italian Twitter users who discussed the 2013 elections would be absent in other political systems. For one thing, the socio-demographic and political characteristics of Italians who engage with politics online -relatively young, well-educated, and highly interested in politics -are similar to those of their Western counterparts (Vaccari, 2013) . The most unique aspect of the Italian 2013 elections that needs to be considered is the success of the internet-enabled Five Star Movement. In our sample, 23% of respondents claimed to have voted for this party, on par with the 25% it achieved nationally, which suggests that our findings are not skewed by an overwhelming presence of Five Star online activists. The Italian electorate itself, however, may be somewhat unique because of the wide appeal of this web-based insurgent party.. Thus while we do not claim to have demonstrated a causal relationship, the results clearly hold out the possibility that political activity on social media could function more as a "gateway drug" leading to offline forms of political activity as opposed to simply a "slacktivist" alternative to such activity. In particular, our findings undermine popular pessimistic views that lower-threshold political talk on social media displaces citizens' time and energy from other forms of higherthreshold engagement, as well as skeptical perspectives suggesting that these forms of involvement are irrelevant. If learning and talking about politics on Twitter really distracted people from other opportunities to take action, we would have expected negative rather than positive correlations between lower-and higher-threshold endeavors. The positive correlations we found are empirically relevant, and politically consequential, regardless of whether our sample of respondents became more engaged because they talked about politics on social media or talked about politics on social media because they were active in politics. Moreover, our study of a subset of Twitter users confirms previous studies that have shown online political information and discussion to be conducive to participation as well as more recent studies that emphasize the role of self-expression -and its enhanced possibilities via social media -as a precursor to other types of engagement.. Finally, as suggested by Bimber et al. (2012) , the ubiquity of digital media has changed the context for participation, and understanding the implications of this change for institutions, organizations, and citizens may be as important as disentangling specific causal patterns linking internet use with political behavior. Even if the associations we found depended solely on the fact that those who are already engaged in other types of political action also turn to social media rather than the other way around, this pattern still opens interesting possibilities for indirect mobilization processes. Citizens who engage in online political actions will also intensely communicate about those actions on social media, which may then lead the people in their online networks to learn about opportunities to engage and to become more motivated to participate. This two-step flow of engagement could not take place unless there was a strong link between information and expression on social media and participation in other types of activities, consistent with our main findings.

B I O O O B I O O O O O O O O O O B O O B O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O B I O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O


Bin Packing with Fragmentable Items: Presentation and Approximations We consider a variant of the Bin Packing Problem dealing with fragmentable items. Given a fixed number of bins, the objective is to put all the items into the bins by splitting them in a minimum number of fragments. This problem is useful for modeling splittable resource allocation. In this paper we introduce the problem and its complexity then we present a -approximation algorithm for a special case in which all bins have the same capacities. The bin packing problem is a widely studied problem. In its standard form, many results have been proposed (see for instance [3] , [8] , [10] ) as well as on approximation algorithms for this problem [1] , [11] . A variant of this problem has been proposed to model a problem of VLSI Circuit design [2] . In this variant, it is allowed to split an item into two or more fragments. Each fragment needs an additional space to be packed and the objective is to minimize the number of bins used. In [12] , the application is a scheduling problem in CATV (Community Antenna TeleVision) networks. Again, it is possible to fragment items and two variants are considered. In the first one, as in [2] , overhead units are added to the size of each fragment. The second concerns the bin packing problems where a cost function has to be minimized (the processing time or the reassembly delay in their scheduling application). Each fragmentation induces an extra cost in this case.. In this paper, we study a new variant in which the number of bins is fixed and items are fragmentable but without additional space. The goal is there to put the items into the bins by splitting them in a minimum number of fragments. This variant is usefull to modelize splittable resource allocation such as the two following applications.. The first application deals with settling accounts. A group of friends goes in holidays. Common charges, such as food, locations ... are payed by some people of the group and recorded in a list. At the end of the holidays the friends settle accounts. Some of them have payed more and need to be refunded by those who have payed less. Obviously, they would like to make a minimum of money transferts. In such an application, a bin corresponds a member of the group who has to be refunded while an item is a member who has to pay. The total size of items is equal to the total space of bins. Finally, each money transfert (a cheque for instance) corresponds to one fragment.. The second application is the wavelength assignment. In optical networks using POADM (Packet Optical Add/Drop Multiplexer) technology [5] , [4] , a node is able to send trafic on any wavelength but it could read trafic on a limited number of wavelengths. The least wavelengths are read, the least energy is consumed. The problem is to assign the trafic sent by node to wavelengths in a way which allows a receiver node to read a minimum number of wavelengths. As it can be seen on Fig. 2 , this application also corresponds to a bin packing with fragmentable items. The items are the transmitting nodes with the quantity of trafic they have to send while the bins are the wavelengths. Here, the total size of the items could differ from the total space of the bins but, on another hand, all the bins have the same capacity that was not the case in the first application. Figure 1 : Four nodes send different amount of traffic to four receiver nodes. Traffic sent from node S 4 to R 4 is split on two wavelengths. R 1 , R 2 and R 3 read one wavelength but R 4 have to read two wavelengths. By switching the trafic from S 2 on the first wavelength, we can assign all trafic from R 4 to the second wavelength. Then R 4 reads only one wavelength and saves power.. A related problem can be found in wireless networks but the problem is studied in two dimensions [7] . Due to its complexity , it has been solved using simple heuristic algorithms without performance guarantee. To the best of our knowledge no other work deals with this variant of the bin packing problem.. The remainder of this paper is organized as follows: Section 2 describes the problem, proves its complexity and presents some general properties; Section 3 describes algorithms and particulary a 6 5 -approximation. Finally, Section 4 con-cludes this paper by summarizing its main achievements and discussing further work. In this paper a new variant of bin packing problem has been introduced. The items are allowed to be splitted into several fragments so that all the items can fill a given number of bins but the total number of fragments has to be minimized. This problem is specially usefull to model splittable resource allocation. We have first defined this problem formally and presented properties on optimal solutions. We have then presented a family of approximation algorithms for instances of the problem in which the bins are all of the same size and each item is smaller than a bin. The best one provides a 6 5 approximation ratio.. Many questions remain open but we think that the following ones are the most important. First is it possible to provide a better approximation ratio than 6 5 . Then, how to generalize the approximation algorithm to the general case where the bins can have different capacities. Finally, which optimization methods -heuristics and exact methods -can be proposed to efficiently solve this problem.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O


CADRE: The CArma Data REduction pipeline The Combined Array for Millimeter-wave Astronomy (CARMA) data reduction pipeline (CADRE) has been developed to give investigators a first look at a fully reduced set of their data. It runs automatically on all data produced by the telescope as they arrive in the CARMA data archive. CADRE is written in Python and uses Python wrappers for MIRIAD subroutines for direct access to the data. It goes through the typical reduction procedures for radio telescope array data and produces a set of continuum and spectral line maps in both MIRIAD and FITS format. CADRE has been in production for nearly two years and this paper presents the current capabilities and planned development. The Combined Array for Millimeter-wave Astronomy (CARMA) radio telescope array is located in the Inyo mountains in California, USA. The array is heterogeneous and is composed of 23 antennas (six 10 m dishes, nine 6.1 m dishes, and eight 3.5 m dishes). The array observes in the 1mm, 3mm, and 1cm wavelength regimes, in both continuum and spectral line modes, and has dual polarization capabilities at 1mm. The array can observe in two independent subarrays, observing different sources at different frequencies with different correlator configurations at the same time. All data produces by the telescope are in the MIRIAD [2, 3] format.. The primary purpose of CADRE [1] is to give the investigators a quick first look at a fully reduced version of their data. This reduced data is of the quality produced by the average user. CADRE runs automatically on all CARMA data as it arrives in the CARMA archive.. CADRE is capable of reducing the following observing modes: continuum, spectral line, mixed mode (spectral and continuum in the same track), single pointings, multipoint mosaics, and SunyaevZel'dovich effect. Future upgrades of CADRE will be able to reduce dual polarization, full stokes, and CARMA23 (all 23 antennas observing together) data. This paper has introduced the CArma Data REduction pipeline (CADRE) and gives a detailed description of its processes. CADRE goes through typical data reduction procedures for radio telescope array data and produces maps to give the investigator(s) a first look at the quality calibratability of their data. All CADRE products are stored in and retrievable from the CARMA data archive, with the same proprietary access restrictions as the raw CARMA data. CADRE will continue to be developed to handle more of CARMA's current and future capabilities.

O O O B I I O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


A multiscale decomposition approach to detect abnormal vasculature in the optic disc This paper presents a multiscale method to detect neovascularization in the optic disc (NVD) using fundus images. Our method is applied to a manually selected region of interest (ROI) containing the optic disc. All the vessels in the ROI are segmented by adaptively combining contrast enhancement methods with a vessel segmentation technique. Textural features extracted using multiscale amplitude-modulation frequency-modulation, morphological granulometry, and fractal dimension are used. A linear SVM is used to perform the classification, which is tested by means of 10-fold cross-validation.The performance is evaluated using 300 images achieving an AUC of 0.93 with maximum accuracy of 88%. Diabetic retinopathy (DR) is one of the leading causes of blindness in the world (Bhavsar et al., 2010) . The disease is asymptomatic in its early stages and can be best managed by the patient by maintaining tight blood sugar and blood pressure control. However, as the disease progresses, it can become sight threatening. Studies (Aiello et al., 2005; Klein et al., 1989) have demonstrated that 50% of type I diabetics and 20% of patients with type II diabetes will progress to advanced stages of DR some time in their lives. One of these advanced stages is proliferative diabetic retinopathy (PDR). PDR is characterized by the appearance of new, abnormal vessels in the retina.. Depending on the location of these new vessels, they can be classified as neovascularization on the optic disc (NVD), where new vessels grow on or within 1 disc diameter (DD) of the optic disc, or neovascularization elsewhere (NVE), where the new vessels are present anywhere outside this NVD region. This paper focuses on the detection of NVD. In early stages, NVD appears as loops or networks of fine vessels (Jelinek and Cree, 2009) . As the disease progresses, the vessels extend outside the optic disc margin and their caliber increases. These new vessels are fragile and can grow into the vitreous gel.. Vitreous traction with normal eye movement may lead to the rupture of the new vessels, causing hemorrhages and significant vision loss. Timely treatment with laser photocoagulation can slow progression of the disease.. Therefore, detection of these new vessels is of critical clinical importance.. Most of the methodologies used to detect DR have been focused on finding other pathologies such as microaneurysms, hemorrhages, and hard exudates, as summarized in Winder et al. (2009) , while a few have looked for vascu-lar abnormalities (Gregson et al., 1995; Gang et al., 2002 ). An approach to detect NVD has been presented by Goatman et al. (2011) . In their paper, vessel segments were separated into abnormal and normal classes. Vessellike candidate segments on the optic papilla are detected by using watershed lines and ridge strength measurements. Fifteen features, including shape, position, brightness, contrast, and density, were extracted from each candidate. Gaussian-kernel support vector machines (SVM) was used to classify data represented by those features. The results were validated using leaveone-out cross-validation. Based on 38 NVD and 71 normal cases, the method achieved an area under the receiver operator characteristic curve (AUC) of 0.79 for the detection of segments with NVD and an AUC of 0.91 for the detection of optic discs with neovascularization.. Others papers in the literature are focused in the detection of neovascularization in the images such as Hassan et al. (2012) , in which they combine morphology-based operations, Gaussian filtering, and thresholding techniques. In their approach, 11 images that presented neovascularization were analyzed, obtaining an average sensitivity/specificity of 89%/64%. Lee et al. (2013) proposed a vessel detection method which includes statistical texture analysis, high order spectrum analysis, and fractal analysis for the detection of neovascularization. They obtained an accuracy of 98.5% but good quality images were hand-picked from DR datasets and 27 out of 137 images present neovascularization.. The fundamental advantages from the use of amplitude-modulation frequencymodulation (AM-FM) features have been previously documented in Pattichis (2009); Murray et al. (2012) . In summary, AM-FM models: (i) provide a large number of non-stationary texture features that are meaningful (e.g., instantaneous frequency, instantaneous amplitude), (ii) allow image reconstructions using multi-scale AM-FM decompositions, and (iii) enable the implementation of robust methods (e.g., Murray et al. (2010) ). A summary of recent medical imaging applications is given in Murray et al. (2012) . Beyond DR applications, we note the recent application to MRI images in Loizou et al. (2011) , and tree image analysis in Ramachandran et al. (2011) .. In what follows, we present a summary of our prior research and list the new contributions of the current paper. In Agurto et al. (2010) , we presented an early study of the use of AM-FM methods for DR. The focus of this paper was on the use of AM-FM features for image classification. The results included a summary of classification of retinal images from different risk levels. The statistics for different AM-FM features were compared over regions with different types of lesions. In Yu et al. (2012a) , we presented a robust method for the detection of the optic disc in DR images. The approach did not use AM-FM features. In Agurto et al. (2014) , we presented a multi-scale approach for detecting exudate regions in DR images. In an earlier conference publication in Agurto et al. (2012) , we presented preliminary results over a limited dataset, a reduced set of AM-FM features, and a different classification approach.. The current paper makes the following contribution over our prior research:. • Adaptive vessel segmentation method: A new approach for adaptive vessel segmentation is developed that uses feedback to determine jointly-optimal parameters for image enhancement and segmentation.. This new approach allows the use of different levels of enhancement.. The new approach is described in subsection 3.1.. • Extended texture feature set extraction and comparison: we focus on the development of a multiscale image processing approach to better capture NVD vessel properties such as narrow vessel caliber and tortuosity levels. The paper provides a comparative study that investigates the use of AM-FM features, granulometries, fractal dimension, as well as the combination of all of them together. The paper establishes the performance of each set of texture features independently and shows that the combined use of all of the features yields the best results.. • Analysis of the vasculature: We focus in the characterization of the entire vasculature in the optic disc to determine the presence of neovascularization without the need to analyze each vessel segment independently. By doing so, we obtain high accuracy in the detection of NVD, which is the ultimate goal of this research.. • Large dataset validation: The approach is tested on a larger database than those used in other papers and it is shown to perform better than current techniques for NVD segmentation and detection.. The organization of this paper is as follows. Section 2 describes the database used to test the proposed approach. The methodology is described in section 3. Results and discussion based on 300 images are presented in section 4. Conclusions are presented in section 5. This paper presents a novel methodology for the detection of neovascularization in the optic disc. The focus of this method is not to characterize segments of the vasculature as performed by Goatman et al. (2011) . Instead, we characterize the vasculature as normal or abnormal. The proposed adaptive vessel segmentation method adequately detects neovascularization, allowing us to correctly extract features of these structures, thus minimizing the inclusion of spurious information from other structures in the retina. By combining an adaptive vessel segmentation approach with the features extracted using AM-FM, granulometry, and spatial information with fractal dimensionality, we have improved upon previous results presented in the automatic classification of NVD Goatman et al. (2011) . The significance of these results is supported by the fact that we used a medium-scale database com- posed of 300 images, achieving a high generalization capacity. This method can be further improved by optimizing empirically set parameters, the adaptive vessel segmentation iteration, and feature selection. This system can be used in conjunction with an automatic DR screening algorithm to ensure that no sight-threatening conditions due to neovascularization are missed. Since the green channel provides excellent contrast for vessel segmentation Soares et al. (2005) ; Ricci and Perfetti (2007) ; Niemeijer et al. (2004) , we restrict our approach to working with the green image. To avoid possible boundary artifacts, a margin of 60 pixels was added to our region of interest (ROI) of 800 × 800 pixels. However, features were extracted from the ROI only.. The method is summarized in Fig. 2 . First, the vessels are segmented using an adaptive vessel segmentation approach. AM-FM features are then extracted from the segmented vessels areas. Next, we compute the fractal dimension and morphological granulometry from the segmented vessels. The extracted features are classified using an SVM with a linear kernel. We provide further details on the approach in the remaining subsections.

O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O


Real-time path planning for virtual agents in dynamic environments We present a novel approach for real-time path planning of multiple virtual agents in complex dynamic scenes. We introduce a new data structure, Multi-agent Navigation Graph (MaNG), which is constructed from the first-and second-order Voronoi diagrams. The MaNG is used to perform route planning and proximity computations for each agent in real time. We compute the MaNG using graphics hardware and present culling techniques to accelerate the computation. We also address undersampling issues for accurate computation. Our algorithm is used for real-time multi-agent planning in pursuit-evasion and crowd simulation scenarios consisting of hundreds of moving agents, each with a distinct goal. Crowds, ubiquitous in the real world from groups of humans to schools of fish, are vital features to model in a virtual environment. Realistic simulation of virtual crowds have diverse applications in architecture design, emergency evacuation, urban planning, personnel training, education and entertainment. Existing work in this area can be broadly classified into agent-based methods that focus more on individual behavior, or crowd simulations that aim to exhibit emergent phenomena of the groups.. In this paper, we address the problem of collision-free path computation for agents moving in a complex virtual environment. Since individuals constantly adjust their behavior according to dynamic factors (e.g. another approaching individual) in the environment, agent-based techniques that focus on modeling individual behaviors and intents offer many attractive benefits. They often result in more realistic and detailed simulations. One of the key challenges in a large-scale agent-based simulation is global path planning for each virtual agent. The path planning problem can become very challenging for real-time applications with a large group of moving virtual characters, as each character is a dynamic obstacle for other agents. Many prior techniques are either restricted to static environments or perform local collision avoidance computations. The latter can result in unnatural behavior or "getting stuck" in local minima. These problems tend to be more visible in a dynamically changing scene with multiple moving virtual agents. Our approach for motion planning of multiple agents uses the 1 st and the 2 nd order Voronoi diagrams to compute a global navigation data structure, the MaNG. The MaNG graph is the union of the 1 st and the 2 nd order Voronoi graphs and is formally presented in Section 4. We treat each agent as a site (in addition to other obstacles in the environment) and the MaNG is computed. The MaNG can be computed in time O(c), and provides a path of maximal clearance for each agent. In addition, we compute the proximity information from the second order Voronoi diagram [31] and apply it within a potential-field based simulator [16] . Let the number of sites be n, and the size of the grid used to compute the discrete Voronoi diagrams be m × m. We assume the number of agents |P a | = O(n). We now present the time complexity of each stage in our algorithm.. The cost of computing the 1 st and 2 nd order discrete Voronoi diagrams is as follows. The size of the quadtree is O(( . The cost of reading back the framebuffers is O(m 2 ). The cost of extracting the MaNG is O(|E|), where |E| is number of edges in MaNG. From lemma 2, the number of edges in MaNG, |E| ≤ |E 1 |+ |E 2 |, where |E k | is number of edges is VD k (P), and |E k | = O(kn) [9] . Thus cost of extracting the MaNG is O(n). The cost of path planning using A * is typically polynomial in O(|E| + |V|). Therefore cost of computing all paths is O(n(|E|+|V|)) = O(n 2 ). In practice, as shown by Table 1 the associated constant with path planning is much smaller and the bottleneck is the discrete Voronoi diagram computation and graph construction. We now highlight the performance of our algorithm in complex dynamic environments. Our approach can perform real-time path planning for each agent in environments up to 200 agents with different destinations, at the rates of 5 to 20 fps. The discrete Voronoi diagrams are computed on grid of resolution 1K × 1K pixels. The fruit stealing simulation has 64 trees with a varying number of thieves and farmers. The crowd simulation has 15 static obstacles and between 2 and 5 moving cars, with a varying number of humans. The performance of our approach, with a timing breakup is presented in Table 1 . We have implemented our algorithm on a PC running Windows XP operating system with an AMD Opteron 280 CPU, 2GB memory and an NVIDIA 7900 GPU. We used OpenGL as the graphics API and Cg language for implementing the fragment programs. The discrete Voronoi diagram and distance field are computed at 32-bit floating point precision using floating point buffers. The Voronoi diagram is stored in the red channel, and the distance field in the depth buffer. We use stencil tests to disable 2 nd order Voronoi diagram computation in the 1 st order Voronoi regions of the obstacles. In the first pass, the stencil mask is set for all pixels in the 1 st order Voronoi regions of the agents. In the second pass, distance functions are evaluated at pixels with stencil mask set. This optimization speeds up both discrete Voronoi diagram computation and MaNG construction. We perform readback of the discrete Voronoi diagrams and construct the MaNG on the CPU. The optimal path is computed using an A * search with Euclidean distance metric to guide the search.. We use a complete quadtree for Voronoi region culling described in Section 5.1. The depth of the quadtree is set such that one leaf node corresponds to a block of 32 × 32 pixels. We need to determine if a node contains up to 2 sites -hence the number of sites per node is encoded in 1 byte. By using a complete quadtree, the node addresses can be efficiently computed using bit shifts, avoiding pointer addressing.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Bayesian Minimax Estimation of the Normal Model With Incomplete Prior Covariance Matrix Specification Abstract-This work addresses the issue of Bayesian robustness in the multivariate normal model when the prior covariance matrix is not completely specified, but rather is described in terms of positive semi-definite bounds. This occurs in situations where, for example, the only prior information available is the bound on the diagonal of the covariance matrix derived from some physical constraints, and that the covariance matrix is positive semi-definite, but otherwise arbitrary. Under the conditional Gamma-minimax principle, previous work by DasGupta and Studden shows that an analytically exact solution is readily available for a special case where the bound difference is a scaled identity. The goal in this work is to consider this problem for general positive definite matrices. The contribution in this paper is a theoretical study of the geometry of the minimax problem. Extension of previous results to a more general case is shown and a practical algorithm that relies on semi-definite programming and the convexity of the minimax formulation is derived. Although the algorithm is numerically exact for up to the bivariate case, its exactness for other cases remains open. Numerical studies demonstrate the accuracy of the proposed algorithm and the robustness of the minimax solution relative to standard and recently proposed methods.Index Terms-Bayesian point estimate, gamma-minimax, minimax estimator, normal model, prior uncertainty, robust Bayesian analysis, shrinkage method. W E consider the estimation problem of random parameters in the multivariate normal model under the Bayesian paradigm (1) Here, both the measurement noise covariance matrix and the design matrix are known, and the random parameter follows a conjugate prior given as: When this prior is completely specified and both and are invertible, it is widely known [21] that there exists an analytical Bayesian solution to this model given by where (3) (4) The posterior mean minimizes the Bayes risk under the quadratic loss. The analytical solution has led to many widely applicable algorithms, for example, the Kalman filter.. However, complete prior specification may not always be available to a statistician for various reasons, such as, an insufficient number of observations to ensure good domain knowledge, missing and noisy data, or many parameters in large-scale problems [20] . In particular, we consider the situation addressed by Leamer [14] and DasGupta and Studden [9] that the prior belongs to a class of distributions with known mean, and the covariance matrix can only be specified by the upper and lower bounds as (5) (6) where denotes the Löwner partial order for symmetric matrices 1 (i.e., means is positive semi-definite (psd). Similarly, means is strictly positive definite. ) We note that the specification in (6) is not the only unique way to describe the incomplete prior. One may also bound the covariance matrix in terms of a Frobenius norm, for example, as in [12] . Other constraints are also discussed by Eldar and Merhav in [10] . However, we note that the constraint (6) implies constraints on the trace, determinant, and norm but not the converse. Accordingly, if the constraints in [10] are imposed, an analytical minimax solution can be derived from the subsequent results of this work (see Appendix A). The incomplete specification is only for the covariance matrix due to the assumption that, in practice, eliciting the prior mean rather than higher moments is easier for a statistician. More arguments for the constraint (6) are discussed in [9] and references therein.. The above incomplete prior specification problem can be tackled by different approaches under the Bayesian paradigm (a thorough discussion is given in Berger's textbook [3, Ch. 4] ). For example, parametric empirical Bayes treats the variances as hyperparameters that can be estimated from the data. However, there is a problem with passing the uncertainty in the hyperparameter estimates to the final decision for small and moderate size problems unless one develops approximations (such as [17] ) that account for that uncertainty [3, p. 170] . A full Bayesian treatment (i.e., hierarchical Bayes analysis) places hyperpriors on top of the prior distribution and performs nested integrations to obtain the final estimates. Hierarchical Bayes is often robust [3] , but the main drawback is the computational burden, unless one uses approximations by assuming other parametric forms for the hyperpriors. We note that the estimation problem of normal means under both empirical and hierarchical Bayes analysis is well documented in [3, Ch. 4] .. In this work, we are interested in an approach within the Bayesian paradigm that is concerned more with the sensitivity of the analysis to possible mis-specification of the prior distribution. Given a class of plausible prior distributions that a statistician can elicit, robust Bayesian analysis finds a decision rule that is optimized for the worst-case scenarios. In other words, robust Bayesian analysis ensures that the decision made is guarded against the least favorable prior in [3] , [24] . Such a minimax approach is used by many statistical decision procedures [2] , [6] , [8] . Even in the robust Bayesian frameworks, there are numerous ways to design procedures that possess either prior or posterior robustness (see [3, Ch. 4.7] for more details). For the problem under consideration, we propose to follow the conditional -minimax framework that was first posed by Watson [25] and subsequently studied in [4] , [9] , and [24] . The key difference with respect to the classical -minimax framework [3] , [24] is that it does not integrate over unobserved data to obtain robustness. We also note that there are other variations of the -minimax principle such as the -minimax regret [3] , [24] . Our aim in this work is not to advocate any particular Bayesian approach 2 . Rather, our main goal is to extend the previous work by DasGupta and Studden [9] , who have solved this problem for a special case. More specifically, we place no restriction on the bounds of the covariance matrix. Our first major contribution is a theoretical result (Theorem 3) that indicates when an analytical minimax solution is available and it covers previous results by DasGupta and Studden [9] as a special case. The second contribution is an algorithm to compute the minimax solution when such an analytical result is not available. This algorithm exploits the geometry of the minimax problem and is based on semi-definite programming. Our theoretical analysis of the algorithm indicates that the algorithm is numerically exact for the bivariate case (i.e.,. ). Further numerical studies suggest that it is also numerically exact for . However, its exactness for is an open question. The paper is organized as follows. In Section II, we detail the -minimax approach and the geometry of the minimax problem. We then present a theoretical study of this problem 2 A complete discussion on robust Bayesian analysis is given in [3] and a comparison between some robust Bayesian methods is given in [9] and specify the conditions for when an analytical solution is available, thereby extending the previous result of DasGupta and Studden [9] . When the analytical solution does not exist, we provide a numerical algorithm that is based on semi-definite programming and exploits the convexity of the minimax formulation, to compute the minimax solution. In Section III, we perform numerical studies to investigate the accuracy and compare the proposed method to some commonly used Bayesian and recently proposed methods [10] . Concluding remarks are given in Section IV.. Notation: The field of real numbers is denoted as , whilst denotes a -dimensional vector space over . Vector quantities are in lower-case bold-face (e.g., ), matrix quantities are in upper-case bold-face (e.g., ), set quantities are in calligraphic letters (e.g., ), denotes expectation, denotes trace, denotes the boundary of a set. For technical clarity, the statement means is positive semi-definite singular (i.e., at least one eigenvalue of is zero). Finally, all technical proofs are detailed in the Appendices. We addressed the robustness issue with respect to prior uncertainty in the multivariate normal model. This problem is practically important for Bayesian data analysis where one cannot obtain a complete prior specification. A theoretical study on the minimax solution was conducted under the Bayesian conditional -minimax approach. An extension to a previous result by DasGupta and Studden, when the ellipsoidal bound of the conditional mean is not spherical, was obtained. For the more general case, we proposed a practical algorithm to compute the minimax estimate. This algorithm is numerically exact for the case and is based on a geometrical interpretation of the space of the posterior mean, and by exploiting the problem's geometry. We also discussed technical issues related to implementation. Numerical studies show that the proposed algorithm improves minimax solution accuracy in the general case and achieves robustness as well as desirable MSE properties.

O O O O O B I O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B I B I B I B I I B I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Application-level graphic streaming channel Scene Graph APIs are used to interact at the application level with a 2D or 3D scene. Examples of such APIs are the External Authoring Interface for VRML scenes or the MPEG-J scene graph API for MPEG-4 scenes. In theory, a remote or local application could interact with the scene using these APIs. But in practice, the application is running in the scene player as a java applet or MPEGlet. This paper shows how a remote scene graph API can be implemented by defining a new graphic streaming channel at the application level. We describe a simple and compact communication protocol corresponding to this streaming channel and give some results of use of this channel. A comparison between EAI and MPEG-J scene graph is also presented. Virtual Reality Modeling Language (VRML) is a text file format used to describe interactive 3D objects and worlds [1, 9] . MPEG-4 has extended this language with new nodes and streaming channels for audio, video and graphics [1, 7] . The graphics channel is a binary format called BIFS for Binary Format for Scene [1, 7] . BIFS has been defined to stream graphics elements directly in the scene graph. MPEG-4 can handle 3D graphics objects with streaming media such as text, audio, video and images. MPEG-4 players, as well as authoring tools for the creation of MP4 files, are becoming available on different platforms, such as desktop computers, mobiles or set-top boxes.. A scene graph API specifies the communication interface between a scene and an application. Examples of such API are the External Authoring Interface [10] for VRML, and the MPEG-J Scene Graph API [6] for MPEG-4. Thanks to these kinds of API, an application can interact with the scene in the following ways:. • Creating or deleting nodes on the scene graph. This functionality is given by a programming interface that initializes the access to the scene graph.. • Sending an event to a node, modifying the field's values. For example, to change the position or colors of a node.. • Sending an event to a node, to read the current value of one of its fields. For example, to get the current position or color of an object.. • To be notified, by means of events, when the value of a field on a node was modified. For example, when an object is clicked.. To play a VRML or MPEG-4 scene a player [2, 11] is necessary. An external application can interact with the scene using the scene graph API of the player. Both EAI and MPEG-J are not limited to a local implementation, but in practice the player and the external application run both in the same local program. For VRML, the local program is a Web browser (Internet Explorer, Netscape), the VRML player is a plug-in and the external application is a java applet. For MEPG-4, we have a similar situation, but where the delivery mechanism change. The external application is called MPEGlet [6] and is streamed to the MPEG-4 player via a MPEG-J channel (figure 1). Thanks to definition of a new graphic stream channel and a compact communication protocol, we have shown how remote scene graph architecture can be implemented. This applicationlevel streaming channel represents an easy way to put new services at run-time in a running MPEG-4 or VRML world. It is, to our knowledge, the only existing remote implementation of type scene graph, although a standard as EAI speaks about it explicitly. The main idea behind it, is to let the player offers its scene graph API as a service to service providers. We are now using the Jini Connection technology [3, 4] to let service providers find in a standardized way the objects that implement the remote scene graph API (the player publishes in a Jini Lookup Service its remote scene graph API). Our ultimate goal is to be able to bring an MPEG-4 player in a Jini federation both as a client and a service.. In addition, we have shown that the MPEG-J scene graph API is a subset of the ISO VRML-EAI. The main missing feature being the creation of new nodes from a string description. Another difference is inside vs outside. In VRML, outside is clearly an HTML page and this html page is used by the EAI to draw objects like buttons or menus. In MPEG-4 scene, no outside can be presupposed, but the inside can be populated with menus or buttons through new nodes called layer2D and layer3D. he response time between the request's send and the return of the results may be influenced by the complexity of the scene. Indeed, by making a simple test of creation of objects, one discovers that after a certain number of objects in the scene, the response time is degraded. We carried out an evaluation of the response time to have an estimate of the time taken by the system in coding/decoding the requests and the results. All the tests were carried out on a local area network.. The first test corresponded to the creation of objects and its placement inside an initially empty scene graph. The application test did a sequential creation of objects (spheres) until arriving to the desired quantity. As table 2 and the figure 7 show, when the creation exceeds 500 objects, the average response time increases. The second test carried out corresponds to the modification of the properties of the objects on the scene. The application creates a whole set of objects (spheres). After this, the position of each object was modified. This time, the number of objects in the scene also influences the response time, however it is observable only over 4000 objects (table 3 and figure 8 ). This architecture and protocol were validated by means of a complete implementation. For this, we have defined a connection protocol to set up a graphic streaming channel between the remote application and the player. This protocol has been designed to allow the set-up of multiple channels.. The wrapper, which belongs to the player, owns a TCP/IP server socket. This server socket waits for a remote application to open two socket connections. For each connection, the application receives a connection ID and after that, sends a message to the wrapper indicating which socket will be used for request messages and which will be used for events messages. In our implementation, the player (wrapper) can accept a single connection as well as multiple connections (figure 6). This allows several remote applications to interact with the scene.. Our MPEG-4 3D player, called SoNG [11] , is running inside Internet Explorer as an active-X component. This plug-in provides a complete java implementation of the External Authoring Interface. Our wrapper is implemented as a signed java applet. The other way to implement it could have been as a COM component in C++.

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