We extend the Iterative Closest Point (ICP) algorithm to obtain a method for vontinuous-time traj... more We extend the Iterative Closest Point (ICP) algorithm to obtain a method for vontinuous-time trajectory estimation (CICP) suitable for SLAM from actuated lidar. Traditional solutions to SLAM from actuated lidar rely heavily on the accuracy of an auxiliary pose sensor to form rigid frames. These frames are then used with ICP to obtain accurate pose estimates. However, since lidar records a single range sample at time, any error in inter-sample sensor motion must be accounted for. This is not possible if the frame is treated as a rigid point cloud. In this work, instead of ICP we estimate a continuous-time trajectory that takes into account inter-sample pose errors. The trajectory is represented as a linear combination of basis functions and formulated as a solution to a (sparse) linear system without restrictive assumptions on sensor motion. We evaluate the algorithm on synthetic and real data and show improved accuracy in open-loop SLAM in comparison to state-of-the-art rigid registration methods.
The innovative Student Technology ExPerience (iSTEP) is a new internship program offered by TechB... more The innovative Student Technology ExPerience (iSTEP) is a new internship program offered by TechBridgeWorld research group at Carnegie Mellon University. iSTEP provides Carnegie Mellon students and recent graduates with an opportunity to work in a multidisciplinary and globally distributed team to develop needs-based computing technology solutions in collaboration with developing communities.
This technical report retrospectively collects the final reports of the undergraduate Computer Sc... more This technical report retrospectively collects the final reports of the undergraduate Computer Science majors from the Qatar Campus of Carnegie Mellon University who elected to complete a senior research thesis in the academic year 2008-09 as part of their degree. These projects have spanned the students' entire senior year, during which they have worked closely with their faculty advisors to plan and carry out their projects. This work counts as 18 units of academic credit each semester. In addition to doing the research, the students presented a brief midterm progress report each semester, presented a public poster session in December, presented an oral summary in the year-end campus-wide Meeting of the Minds and submitted a written thesis in May.
We propose an automated method to recover the full calibration parameters between a 3D range sens... more We propose an automated method to recover the full calibration parameters between a 3D range sensor and a monocular camera system. Our method is not only accurate and fully automated, but also relies on a simple calibration target consisting of a single circle. This allows the algorithm to be suitable for applications requiring in-situ calibration. We demonstrate the effectiveness of the algorithm on a cameralidar system and show results on 3D mapping tasks.
Stereo visual odometry and dense scene reconstruction depend critically on accurate calibration o... more Stereo visual odometry and dense scene reconstruction depend critically on accurate calibration of the extrinsic (relative) stereo camera poses. We present an algorithm for continuous, online stereo extrinsic re-calibration operating only on sparse stereo correspondences on a per-frame basis. We obtain the 5 degree of freedom extrinsic pose for each frame, with a fixed baseline, making it possible to model time-dependent variations. The initial extrinsic estimates are found by minimizing epipolar errors, and are refined via a Kalman Filter (KF). Observation covariances are derived from the Crámer-Rao lower bound of the solution uncertainty. The algorithm operates at frame rate with unoptimized Matlab code with over 1000 correspondences per frame. We validate its performance using a variety of real stereo datasets and simulations.
Although para-social workers carry the primary responsibility in providing essential services to ... more Although para-social workers carry the primary responsibility in providing essential services to the growing population of orphans and vulnerable children in Tanzania, they are often not paid for this work. Moreover, these para-social workers are unable to access governmental resources due to the lack of an efficient means of reporting their needs to relevant government officials in a timely manner. In this paper we describe a text message (SMS) based solution that harnesses the prevalence of mobile phones coupled with several Open Source tools to empower these para-social workers. Specifically, we build a more efficient mechanism for reporting summary data on orphans and vulnerable children to relevant government officials in a cost-effective and efficient manner. This paper reports on our needs assessment process, reviews the related work, describes the implementation and testing of our prototype solution, and concludes with a discussion of relevant future work.
Liquid Natural Gas (LNG) processing facilities contain large complex networks of pipes of varying... more Liquid Natural Gas (LNG) processing facilities contain large complex networks of pipes of varying diameter and orientation intermixed with control valves, processes and sensors. Regular inspection of these pipes for corrosion, caused by impurities in the gas processing chain, is critical for safety. Popular existing non-destructive technologies that used for corrosion inspection in LNG pipes include Magnetic Flux Leakage (MFL), radiography (X-rays), and ultrasound among others. These methods can be used to obtain measurements of pipe wall thickness, and by monitoring for changes in pipe wall thickness over time the rate of corrosion can be estimated. For LNG pipes, unlike large mainstream gas pipelines, the complex infrastructure means that these sensors are currently employed external to the pipe itself making comprehensive, regular coverage of the pipe network difficult to impossible. As a result, a sampling-based approach is taken where parts of the pipe network are sampled regularly, and the corrosion estimate is extrapolated to the remainder of the pipe using predictive corrosion models derived from metallurgical properties. We argue that a robot crawler that can move a suite of sensors inside the pipe network, can provide a mechanism to achieve more comprehensive and effective coverage. In this technical report, we explore a vision-based system for building 2D registered appearance maps of the pipe surface whilst simultaneously localizing the robot in the pipe. Such a system is essential to provide a localization estimate for overlaying other non-destructive sensors, registering changes over time, and the resulting 2D metric appearance maps may also be useful for corrosion detection. For this work, we restrict ourselves to linear pipe formations.
Monocular visual odometry for robot localization in LNG pipes
Regular inspection for corrosion of the pipes used in Liquified Natural Gas (LNG) processing faci... more Regular inspection for corrosion of the pipes used in Liquified Natural Gas (LNG) processing facilities is critical for safety. We argue that a visual perception system equipped on a pipe crawling robot can improve on existing techniques (Magnetic Flux Leakage, radiography, ultrasound) by producing high resolution registered appearance maps of the internal surface. To achieve this capability, it is necessary to estimate the pose of sensors as the robot traverses the pipes. We have explored two monocular visual odometry algorithms (dense and sparse) that can be used to estimate sensor pose. Both algorithms use a single easily made measurement of the scene structure to resolve the monocular scale ambiguity in their visual odometry estimates. We have obtained pose estimates using these algorithms with image sequences captured from cameras mounted on different robots as they moved through two pipes having diameters of 152mm (6") and 406mm (16"), and lengths of 6 and 4 meters respectively. Accurate pose estimates were obtained whose errors were consistently less than 1 percent for distance traveled down the pipe.
ABSTRACT Pipe inspection is a critical activity in gas pro- duction facilities and many other ind... more ABSTRACT Pipe inspection is a critical activity in gas pro- duction facilities and many other industries. In this paper, we contribute a stereo visual odometry system for creating high resolution, sub-millimeter maps of pipe surfaces. Such maps provide both D structure and appearance information that can be used for visualization, cross registration with other sensor data, inspection and corrosion detection tasks. We present a range of optical configuration and visual odometry techniques that we use to achieve high accuracy while minimizing specular reflections. We show empirical results from a range of datasets to demonstrate the performance of our approach.
ABSTRACT Pipe inspection is a critical activity in gas pro- duction facilities and many other ind... more ABSTRACT Pipe inspection is a critical activity in gas pro- duction facilities and many other industries. In this paper, we contribute a stereo visual odometry system for creating high resolution, sub-millimeter maps of pipe surfaces. Such maps provide both D structure and appearance information that can be used for visualization, cross registration with other sensor data, inspection and corrosion detection tasks. We present a range of optical configuration and visual odometry techniques that we use to achieve high accuracy while minimizing specular reflections. We show empirical results from a range of datasets to demonstrate the performance of our approach.
Despite the importance of literacy to most aspects of life, underserved communities continue to s... more Despite the importance of literacy to most aspects of life, underserved communities continue to suffer from low literacy rates; especially for globally prevalent languages such as English. This is particularly problematic since English literacy is an important skill for increased access to income generation and higher education opportunities in these communities. Teaching English in underserved communities can be challenging due to a variety of obstacles. In this paper we report on our work with a primary school in Tanzania, with migrant workers in Doha, and with a school for the deaf in the USA to address some of these challenges using web technology and mobile phones. We developed a web-accessible content authoring tool that teachers can use to create and modify English grammar exercises, and a simple game that students use on a mobile phone to practice the content uploaded from the authoring tool. Our solution is primarily intended to increase the motivation for practicing English grammar among students, and thereby enhance English literacy in underserved communities. Feedback from teachers and students in all of our field studies indicate this solution is affordable and has significant potential to enhance the English classroom and homework experience.
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Papers by Hatem Alismail