Probing crowd density through smartphones in city-scale mass gatherings

EPJ Data Science

Table 2 Overview of technologies and methods for crowd density assessment

Sensor modality	Class	Method	Reference
Video	Holistic	Optical flow	[19]
		Fractal dimension	[41]
		Pixel counting	[42]
		Machine learning	[43]
	Object-based	Trajectories	[22, 28]
		Supervised classification	[44]
		Unsupervised clustering	[45]
		Social force model	[26]
Smartphone	In-network	CDR	[32, 33]
	In-network	Network bandwidth usage	[31, 46]
	On-device	Trajectories	[14, 38]
	Other	Bluetooth beacons	[39, 47]

Overview of technologies and methods to automatically to assess crowd density. Different video-based approaches have been investigated, a selection of methods is given here. Thanks to the location-awareness of modern smartphones, they have increasingly been considered as an alternative platform for crowd monitoring.