References of "Liu, Feng"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailBuilding a validation measure for activity-based transportation models based on mobile phone data
Liu, Feng; Janssens, Davy; Cui, JianXun et al

in Expert Systems with Applications (2014), 41(14), 6174-6189

Activity-based micro-simulation transportation models typically predict 24-h activity-travel sequences for each individual in a study area. These sequences serve as a key input for travel demand analysis ... [more ▼]

Activity-based micro-simulation transportation models typically predict 24-h activity-travel sequences for each individual in a study area. These sequences serve as a key input for travel demand analysis and forecasting in the region. However, despite their importance, the lack of a reliable benchmark to evaluate the generated sequences has hampered further development and application of the models. With the wide deployment of mobile phone devices today, we explore the possibility of using the travel behavioral information derived from mobile phone data to build such a validation measure. Our investigation consists of three steps. First, the daily trajectory of locations, where a user performed activities, is constructed from the mobile phone records. To account for the discrepancy between the stops revealed by the call data and the real location traces that the user has made, the daily trajectories are then transformed into actual travel sequences. Finally, all the derived sequences are classified into typical activity-travel patterns which, in combination with their relative frequencies, define an activity-travel profile. The established profile characterizes the current activity-travel behavior in the study area, and can thus be used as a benchmark for the assessment of the activity-based transportation models. By comparing the activity-travel profiles derived from the call data with statistics that stem from traditional activity-travel surveys, the validation potential is demonstrated. In addition, a sensitivity analysis is carried out to assess how the results are affected by the different parameter settings defined in the profiling process. [less ▲]

Detailed reference viewed: 24 (3 ULg)
Full Text
Peer Reviewed
See detailSemantic Annotation of Global Positioning System Traces: Activity Type Inference
Reumers, Sofie; Liu, Feng; Janssens, Davy et al

in Transportation Research Record: Journal of the Transportation Research Board (2013), 2383

Because of the rapid development of technology, larger data sets on activity travel behavior have become available. These data sets often lack semantic interpretation. This lack of interpretation implies ... [more ▼]

Because of the rapid development of technology, larger data sets on activity travel behavior have become available. These data sets often lack semantic interpretation. This lack of interpretation implies that annotation of activity type and transportation mode is necessary. This paper aims to infer activity types from Global Positioning System (GPS) traces by developing a decision tree-based model. The model considers only activity start times and activity durations. On the basis of the decision tree classification, a probability distribution and a point prediction model were constructed. The probability matrix described the probability of each activity type for each class (i.e., combination of activity start time and activity duration). In each class, the point prediction model selected the activity type that had the highest probability. Two types of data were collected in 2006 and 2007 in Flanders, Belgium (i.e., activity travel data and GPS data). The optimal classification tree constructed contained 18 leaves. Consequently, 18 if-then rules were derived. An accuracy of 74% was achieved when the tree was trained. The accuracy of the model for the validation set (72.5%) showed that overfitting was minimal. When the model was applied to the test set, the accuracy was almost 76%. The models indicated the importance of time information in the semantic enrichment process. This study contributes to future data collection in that it enables researchers to infer activity types directly from activity start time and duration information obtained from GPS data. Because no location information is needed, this research can be easily and readily applied to millions of individual agents. [less ▲]

Detailed reference viewed: 123 (5 ULg)
Full Text
Peer Reviewed
See detailProfiling workers’ activity-travel behavior based on mobile phone data
Liu, Feng; Janssens, Davy; Wets, Geert et al

in Proceedings of the Third International Conference on the Analysis of Mobile Phone Datasets (NetMob) (2013)

Activity-based micro-simulation models typically predict 24-hour activity-travel patterns for each individual in a study area. These patterns reflect the characteristics of the available transportation ... [more ▼]

Activity-based micro-simulation models typically predict 24-hour activity-travel patterns for each individual in a study area. These patterns reflect the characteristics of the available transportation infrastructure and land-use system as well as individuals’ lifestyles and needs. However, the lack of a reliable benchmark to evaluate the generated patterns has been a major concern. To address this issue, we explore the possibility of using mobile phone data to build such a validation measure. Our investigation consists of three steps. First, the daily trajectory of locations, where a user performed activities, is constructed from the mobile phone records. To account for the discrepancy between the movements revealed by the call data and the real traces that the user has made, the daily trajectories are then transformed into travel sequences. Finally, all the inferred travel sequences are classified into typical activity-travel patterns which, in combination with their relative frequencies, define a profile. The established profile represents the activity-travel behavior in the study area, and thus can be used as a benchmark for the validation of the activity-based models. By comparing the benchmark profiles derived from the call data with statistics that stem from activity-travel surveys, the validation potential is demonstrated. In addition, a sensitivity analysis is carried out to assess how the results are affected by the different parameter settings defined in the profiling process. [less ▲]

Detailed reference viewed: 50 (0 ULg)
Full Text
Peer Reviewed
See detailAnnotating mobile phone location data with activity purposes using machine learning algorithms
Liu, Feng; Janssens, Davy; Wets, Geert et al

in Expert Systems with Applications (2013), 40(8), 32993311

Individual human travel patterns captured by mobile phone data have been quantitatively characterized by mathematical models, but the underlying activities which initiate the movement are still in a less ... [more ▼]

Individual human travel patterns captured by mobile phone data have been quantitatively characterized by mathematical models, but the underlying activities which initiate the movement are still in a less-explored stage. As a result of the nature of how activity and related travel decisions are made in daily life, human activity-travel behavior exhibits a high degree of spatial and temporal regularities as well as sequential ordering. In this study, we investigate to what extent the behavioral routines could reveal the activities being performed at mobile phone call locations that are captured when users initiate or receive a voice call or message. Our exploration consists of four steps. First, we define a set of comprehensive temporal variables characterizing each call location. Feature selection techniques are then applied to choose the most effective variables in the second step. Next, a set of state-of-the-art machine learning algorithms including Support Vector Machines, Logistic Regression, Decision Trees and Random Forests are employed to build classification models. Alongside, an ensemble of the results of the above models is also tested. Finally, the inference performance is further enhanced by a post-processing algorithm. Using data collected from natural mobile phone communication patterns of 80 users over a period of more than one year, we evaluated our approach via a set of extensive experiments. Based on the ensemble of the models, we achieved prediction accuracy of 69.7%. Furthermore, using the post processing algorithm, the performance obtained a 7.6% improvement. The experiment results demonstrate the potential to annotate mobile phone locations based on the integration of data mining techniques with the characteristics of underlying activity-travel behavior, contributing towards the semantic comprehension and further application of the massive data. [less ▲]

Detailed reference viewed: 61 (1 ULg)
Full Text
Peer Reviewed
See detailSemantic Annotation of GPS Traces: Activity Type Inference
Reumers, Sofie; Liu, Feng; Janssens, Davy et al

in Proceedings of the 92nd Annual Meeting of the Transportation Research Board (DVD-ROM) (2013)

Due to the rapid development of technology, larger data sets concerning activity travel behavior become available. These data sets often lack semantic interpretation. This implies that annotation in terms ... [more ▼]

Due to the rapid development of technology, larger data sets concerning activity travel behavior become available. These data sets often lack semantic interpretation. This implies that annotation in terms of activity type and transportation mode is necessary. This paper aims to infer activity types from GPS traces by developing a decision tree-based model. The model only considers activity start times and activity durations. Based on the decision tree classification, a probability distribution and a point prediction model were constructed. The probability matrix describes the probability of each activity type for each class (i.e. combination of activity start time and activity duration). In each class, the point prediction model selects the activity type that has the highest probability. Two types of data were collected in 2006 and 2007 in Flanders, Belgium, i.e. activity travel data and GPS data. The optimal classification tree constructed comprises 18 leaves. Consequently, 18 if-then rules were derived. An accuracy of 74% was achieved when training the tree. The accuracy of the model for the validation set, i.e. 72.5%, shows that overfitting is minimal. When applying the model to the test set, the accuracy was almost 76%. The models indicate the importance of time information in the semantic enrichment process. This study contributes to future data collection in that it enables researchers to directly infer activity types from activity start time and duration information obtained from GPS data. Because no location information is needed, this research can be easily and readily implemented to millions of individual agents. [less ▲]

Detailed reference viewed: 107 (0 ULg)