In this article we consider the problem of mapping a noisy estimate of a user's current location to a semantically meaningful point of interest, such as a home, restaurant, or store. Despite the poor accuracy of GPS on current mobile devices and the relatively high density of places in urban areas, it is possible to predict a user's location with considerable precision by explicitly modeling both places and users and by combining a variety of signals about a user's current context. Places are often simply modeled as a single latitude and longitude when in fact they are complex entities existing in both space and time and shaped by the millions of people that interact with them. Similarly, models of users reveal complex but predictable patterns of mobility that can be exploited for this task. We propose a novel spatial search algorithm that infers a user's location by combining aggregate signals mined from billions of foursquare check-ins with real-time contextual information. We evaluate a variety of techniques and demonstrate that machine learning algorithms for ranking and spatiotemporal models of places and users offer significant improvement over common methods for location search based on distance and popularity.

Visual and auditory cues are important facilitators of user engagement in virtual environments and video games. Prior research supports the notion that our perception of visual fidelity (quality) is influenced by auditory stimuli. Understanding exactly how our perception of visual fidelity changes in the presence of multimodal stimuli can potentially impact the design of virtual environments, thus creating more engaging virtual worlds and scenarios. Stereoscopic 3-D display technology provides the users with additional visual information (depth into and out of the screen plane). There have been relatively few studies that have investigated the impact that auditory stimuli have on our perception of visual fidelity in the presence of stereoscopic 3-D. Building on previous work, we examine the effect of auditory stimuli on our perception of visual fidelity within a stereoscopic 3-D environment.

Foursquare is a location-based social application that helps users explore the world around them and share their experiences with friends. When foursquare users visit places, they ``check in" using their mobile phones, indicating they are at that place. People check in for a variety of reasons: to keep up with friends, get tips about places, redeem rewards, and keep track of their personal history. In aggregate, billions of these check-ins reveal distinct patterns about when places are popular and allow us to build a unique place recommendation engine which can identify and recommend interesting events in real-time based on statistical deviations from past historical trends.

SPROUT² is a query answering system that allows users to ask structured queries over tables embedded in Web pages, over Google Fusion tables, and over uncertain tables that can be extracted from answers to Google Squared. At the core of this service lies SPROUT, a query engine for probabilistic databases. This demonstration allows users to compose and ask ad-hoc queries of their choice and also to take a tour through the system's capabilities along pre-arranged scenarios on, e.g., movie actors and directors, biomass facilities, or leveraging corporate databases.

Histograms represent a popular means for feature representation. This paper is concerned with the problem of exhaustive histogram-based image search. Several standard histogram construction methods are explored, including the conventional approach, Huangpsilas method, and the state-of-the-art integral histogram. In addition, we present a novel multiscale histogram-based search algorithm, termed the distributive histogram, that can be evaluated exhaustively in a fast and memory efficient manner. An extensive systematic empirical evaluation is presented that explores the computational and storage consequences of altering the search image and histogram bin sizes. Experiments reveal up to an eight-fold decrease in computation time and hundreds- to thousands-fold decrease of memory use of the proposed distributive histogram in comparison to the integral histogram. Finally, we conclude with a discussion on the relative merits between the various approaches considered in the paper.

The underwater environment presents many challenges for robotic sensing including highly variable lighting, the presence of dynamic objects, and the six degree of freedom (6DOF) 3D environment. Yet in spite of these challenges the aquatic environment presents many real and practical applications for robotic sensors. A common requirement of many of these tasks is the need to construct accurate 3D representations of structures in the environment. In order to address this requirement we have developed a stereo vision-inertial sensing device that we have successfully deployed to reconstruct complex 3D structures in both the aquatic and terrestrial domains. The sensor temporally combines 3D information, obtained using stereo vision algorithms with a 3DOF inertial sensor. The resulting point cloud model is then converted to a volumetric representation and a textured polygonal mesh is extracted for later processing. Recently obtained underwater reconstructions of wrecks and coral obtained with the sensor are presented.

The aquatic realm is ideal for testing autonomous robotic technology. The challenges presented in this environment are numerous due to the highly dynamic nature of the medium. Applications for underwater robotics include the autonomous inspection of coral reef, ships, pipelines, and other environmental assessment programs. In this paper we present current results in using 6DOF entropy minimization SLAM (simultaneous localization and mapping) for creating dense 3D visual maps of underwater environments that are suitable for such applications. The proposed SLAM algorithm exploits dense information coming from a stereo system, and performs robust egomotion estimation and global-rectification following an optimization approach

Coral reef health is an indicator of global climate change and coral reefs themselves are important for sheltering fish and other aquatic life. Monitoring reefs is a time-consuming and potentially dangerous task and as a consequence autonomous robotic mapping and surveillance is desired. This paper describes an underwater vision-based sensor to aid in this task. Underwater environments present many challenges for vision-based sensors and robotic vehicles. Lighting is highly variable, optical snow/particulate matter can confound traditional noise models, the environment lacks visual structure, and limited communication between autonomous agents including divers and surface support exacerbates the potentially dangerous environment. We describe experiments with our multi-camera stereo reconstruction algorithm geared towards coral reef monitoring. The sensor is used to estimate volumetric scene structure while simultaneously estimating sensor ego-motion. Preliminary field trials indicate the utility of the sensor for 3D reef monitoring and results of land-based evaluation of the sensor are shown to evaluate the accuracy of the system

We describe recent results obtained with AQUA, a mobile robot capable of swimming, walking and amphibious operation. Designed to rely primarily on visual sensors, the AQUA robot uses vision to navigate underwater using servo-based guidance, and also to obtain high-resolution range scans of its local environment. This paper describes some of the pragmatic and logistic obstacles encountered, and provides an overview of some of the basic capabilities of the vehicle and its associated sensors. Moreover, this paper presents the first ever amphibious transition from walking to swimming.

Existing commercial technologies do not adequately meet the requirements for tracking in fully-enclosed VR displays. We present the Hedgehog, which overcomes several limitations imposed by existing sensors and tracking technology. The tracking system robustly and reliably estimates the 6DOF pose of the device with high accuracy and a reasonable update rate. The system is composed of several cameras viewing the display walls and an arrangement of laser diodes secured to the user. The light emitted from the lasers projects onto the display walls and the 2D centroids of the projections are tracked to estimate the 6DOF pose of the device. The system is able to handle ambiguous laser projection configurations, static and dynamic occlusions of the lasers, and incorporates an intelligent laser activation control mechanism that determines which lasers are most likely to improve the pose estimate. The Hedgehog is also capable of performing auto-calibration of the necessary camera parameters through the use of the SCAAT algorithm. A preliminary evaluation reveals that the system has an angular resolution of 0.01 degrees RMS and a position resolution of 0.2 mm RMS.

This paper describes an underwater walking robotic system being developed under the name AQUA, the goals of the AQUA project, the overall hardware and software design, the basic hardware and sensor packages that have been developed, and some initial experiments. The robot is based on the RHex hexapod robot and uses a suite of sensing technologies, primarily based on computer vision and INS, to allow it to navigate and map clear shallow-water environments. The sensor-based navigation and mapping algorithms are based on the use of both artificial floating visual and acoustic landmarks as well as on naturally occurring underwater landmarks and trinocular stereo.