17 research outputs found
Detecting Flow Anomalies in Distributed Systems
Deep within the networks of distributed systems, one often finds anomalies
that affect their efficiency and performance. These anomalies are difficult to
detect because the distributed systems may not have sufficient sensors to
monitor the flow of traffic within the interconnected nodes of the networks.
Without early detection and making corrections, these anomalies may aggravate
over time and could possibly cause disastrous outcomes in the system in the
unforeseeable future. Using only coarse-grained information from the two end
points of network flows, we propose a network transmission model and a
localization algorithm, to detect the location of anomalies and rank them using
a proposed metric within distributed systems. We evaluate our approach on
passengers' records of an urbanized city's public transportation system and
correlate our findings with passengers' postings on social media microblogs.
Our experiments show that the metric derived using our localization algorithm
gives a better ranking of anomalies as compared to standard deviation measures
from statistical models. Our case studies also demonstrate that transportation
events reported in social media microblogs matches the locations of our detect
anomalies, suggesting that our algorithm performs well in locating the
anomalies within distributed systems
Inferring Unusual Crowd Events From Mobile Phone Call Detail Records
The pervasiveness and availability of mobile phone data offer the opportunity
of discovering usable knowledge about crowd behaviors in urban environments.
Cities can leverage such knowledge in order to provide better services (e.g.,
public transport planning, optimized resource allocation) and safer cities.
Call Detail Record (CDR) data represents a practical data source to detect and
monitor unusual events considering the high level of mobile phone penetration,
compared with GPS equipped and open devices. In this paper, we provide a
methodology that is able to detect unusual events from CDR data that typically
has low accuracy in terms of space and time resolution. Moreover, we introduce
a concept of unusual event that involves a large amount of people who expose an
unusual mobility behavior. Our careful consideration of the issues that come
from coarse-grained CDR data ultimately leads to a completely general framework
that can detect unusual crowd events from CDR data effectively and efficiently.
Through extensive experiments on real-world CDR data for a large city in
Africa, we demonstrate that our method can detect unusual events with 16%
higher recall and over 10 times higher precision, compared to state-of-the-art
methods. We implement a visual analytics prototype system to help end users
analyze detected unusual crowd events to best suit different application
scenarios. To the best of our knowledge, this is the first work on the
detection of unusual events from CDR data with considerations of its temporal
and spatial sparseness and distinction between user unusual activities and
daily routines.Comment: 18 pages, 6 figure
Can multimodal sensing detect and localize transient events?
National Research Foundation (NRF) Singapore under International Research Centres in Singapore Funding Initiativ
Detection of Anomalous Traffic Patterns and Insight Analysis from Bus Trajectory Data
© 2019, Springer Nature Switzerland AG. Detection of anomalous patterns from traffic data is closely related to analysis of traffic accidents, fault detection, flow management, and new infrastructure planning. Existing methods on traffic anomaly detection are modelled on taxi trajectory data and have shortcoming that the data may lose much information about actual road traffic situation, as taxi drivers can select optimal route for themselves to avoid traffic anomalies. We employ bus trajectory data as it reflects real traffic conditions on the road to detect city-wide anomalous traffic patterns and to provide broader range of insights into these anomalies. Taking these considerations, we first propose a feature visualization method by mapping extracted 3-dimensional hidden features to red-green-blue (RGB) color space with a deep sparse autoencoder (DSAE). A color trajectory (CT) is produced by encoding a trajectory with RGB colors. Then, a novel algorithm is devised to detect spatio-temporal outliers with spatial and temporal properties extracted from the CT. We also integrate the CT with the geographic information system (GIS) map to obtain insights for understanding the traffic anomaly locations, and more importantly the road influence affected by the corresponding anomalies. Our proposed method was tested on three real-world bus trajectory data sets to demonstrate the excellent performance of high detection rates and low false alarm rates
Time delay estimation of traffic congestion propagation due to accidents based on statistical causality
The accurate estimation of time delays is crucial in traffic congestion
analysis, as this information can be used to address fundamental questions
regarding the origin and propagation of traffic congestion. However, the exact
measurement of time delays during congestion remains a challenge owing to the
complex propagation process between roads and high uncertainty regarding future
behavior. To overcome this challenge, we propose a novel time delay estimation
method for the propagation of traffic congestion due to accidents using
lag-specific transfer entropy (TE). The proposed method adopts Markov bootstrap
techniques to quantify uncertainty in the time delay estimator. To the best of
our knowledge, our proposed method is the first to estimate time delays based
on causal relationships between adjacent roads. We validated the method's
efficacy using simulated data, as well as real user trajectory data obtained
from a major GPS navigation system in South Korea.Comment: http://www.aimspress.com/article/doi/10.3934/era.202303
Map Matching Based on Conditional Random Fields and Route Preference Mining for Uncertain Trajectories
In order to improve offline map matching accuracy of uncertain GPS trajectories, a map matching algorithm based on conditional random fields (CRF) and route preference mining is proposed. In this algorithm, road offset distance and the temporal-spatial relationship between the sampling points are used as features of GPS trajectory in a CRF model, which integrates the temporal-spatial context information flexibly. The driver route preference is also used to bolster the temporal-spatial context when a low GPS sampling rate impairs the resolving power of temporal-spatial context in CRF, allowing the map matching accuracy of uncertain GPS trajectories to get improved significantly. The experimental results show that our proposed algorithm is more accurate than existing methods, especially in the case of a low-sampling-rate
TRAVEL TIME ESTIMATION USING SPATIO-TEMPORAL INDEX BASED ON CASSANDRA
Travel time estimation plays an important role in traffic monitoring and route planning. Taxicabs equipped with Global Positioning System (GPS) devices have been frequently used to monitor the traffic state, and GPS trajectories of taxicabs also used to estimate path travel time in an urban area. However, in most cases, it is difficult to find a trajectory that fits perfectly with the query path, as some road segments may be traveled by no taxicab in present time slot. This makes it hard to estimate the travel time of the query path. This paper proposes a framework to estimate the travel time of a path by using the GPS trajectories of taxicabs as well as map data sources. In this framework, the travel time is represented as a series of residence time in cells (one cell is the gird segmentation unit), thus the key issues of the estimation are: finding the local traffic patterns of frequently shared paths from historical data and computing the stay time in cells. There are three major processes in this framework: trajectories preprocessing, establishing the temporal-spatial index and cell-based travel time estimation. Based on the temporal-spatial index, an algorithm is developed that uses similar route patterns, the cell-based travel time over a period of history and road network information to estimate the travel time of a path. This paper uses GPS trajectories of 10,357 taxicabs over a period of one week to evaluate the framework. The results demonstrate that this paper’s method is effective and feasible in city-wide scenarios