Structure of the Thesis

The content of this thesis is presented in two parts. In the first part (Synopsis) the above research papers are embedded in the scientific context. In the second part (Research Papers), the papers are presented with the content and format as they were submitted or published. In addition, a summary and key findings of each of these research papers can be found in chapter 3.

After this introductory chapter, the Synopsis continues with the theoretical background and a review of the state of the art (chapter 2). First, some principles of the movement model in mobility data mining and visual analytics disciplines are introduced. The chapter continues with a review to applications of similarity analysis in GKD in movement data. Following this, the concept of similarity for movement data is introduced and relevant techniques are reviewed. The Synopsis proceeds with an introduction to the research process, the methods used in this research, as well as the most relevant results of this study in chapter 3. Afterwards, in chapter 4 the individual contributions of the four papers is put into a broader context and the substances of the papers are discussed. Finally, the synopsis ends with conclusions and an outlook on future research (chapter 5).

Theoretical Background and

State of the Art

The overall aim of this chapter is fourfold: First, to illustrate the concept of movement itself in a generic model and describe the main components of move- ment model that are central to this research (section 2.1). Second, to capture the scope of movement research in a broad perspective (section 2.2) and give an overview of the previous and ongoing trends of research studies on movement (section 2.3). Third, to introduce the process of knowledge discovery in move- ment datasets (section 2.4). And finally, to introduce the movement similarity analysis problem and report on the relevant literature (section 2.5). However, first of all key terms of this thesis need to be explained:

Movement is “a fundamental characteristic of life, driven by processes that act across multiple spatial and temporal scales”. Movement for the purpose of this research is defined as “a change in the spatial location of the whole individual in time”, that is, as whole-body movement (Nathan et al., 2008, p.19052).

Frank (2001, p.22) identifies two forms of change in general: “change of the objects of interest” (appear, disappear, merge, and split); and “change in the position or geometric form of these objects” (move). Specifically, temporal change in the life of an individual (i.e. humans, animals) can take place in three forms of “birth, death, and movement” (Turchin, 1998, p.2). This thesis only deals with movement based on the Lagrangian approach, which in contrast to other forms of change, has at least two dimensions, namely, temporal and spatial (Turchin, 1998). Figure 2.1 represents the movement of an ant in a schematic way.

Trajectory In this thesis, the movement of an individual is represented by its trajectory, also called geospatial lifeline, as a time-ordered set of positions (Laube et al., 2007; Spaccapietra et al., 2008) as shown in Figure 2.1. For practical reasons of measuring or observing the positions of a moving object over time a trajectory consists of a series of discrete space-time observations. In this thesis, an observation point along a trajectory is referred to as a trajectory fix (or fix), like the ones shown in Figure 2.1.

X Y

fix

fix

fix

fix

Figure 2.1: Trajectory of a moving object (an ant), representative of its movement path over time.

Moving object (also called mobile object or dynamic object) is defined as an entity whose position changes over time (e.g. the ant in Figure 2.1). In this thesis, moving objects are conceptualized by moving points, called Moving Point Object (MPO) (i.e. as 0 − D geometric entities). That is, the location of the object in time is considered to be more important than its dimension. Location is usually indicated using geographic coordinates (φ, λ) or Cartesian coordinates (x, y, (z)). Accordingly, in this thesis the location of a moving object at time t is specified by a tuple (x, y(, z), t) of coordinates. We consider two categories of moving objects: a) georeferenced (i.e dynamic objects or processes that move about in geographic space, such as animals, vehicles, humans, and hurricanes); and b) non-georeferenced dynamic objects (i.e. dynamic phenomena that move in a non-geographic space such as gaze point movements of eyes) .

Movement Parameters (MP) comprise the measurable quantities of movements, that can be observed along objects’ geospatial lifelines, and their deriva- tives. Movement parameters are divided into two types of instantaneous parameters (i.e. detectable at individual moments) such as position, speed, acceleration, direction (e.g. as represented by the azimuth Azi at fixi in

Figure 2.1) and relative parameters (i.e. measurable over time intervals) such as relative speed, turning angle, and path sinuosity (Laube et al., 2007; Giannotti and Pedreschi, 2008).

Movement Features are properties of movement parameters of an object, es- sential to characterize its movement. In this thesis, movement features are identified as the amplitude and frequency of the variations of movement parameters.

Movement path How to move? Where to move? Internal state Why move? External factors Movement characteristics Which movement process external factors dynamics

geographic context spatial constraints barriers attractions

internal state dynamics

movement parameters

continuous

discontinuous (stop-and-move) scope of this research

situation? (b)

(d)

(a)

(trajectory)

(c)

Figure 2.2: Conceptual model of movement (an extended version of the framework by Nathan et al., 2008)

Dynamic behavior (also called movement behavior) of a moving object is re- ferred to as the dynamic movement characteristics of an object and the way that the object moves during the whole duration of observation or an episode (Dykes and Mountain, 2003) of its geospatial lifeline. In this thesis, the dynamic behavior gives an indication of variations or trends of movement parameters of the moving object over time.

2.1 Conceptual Model of Movement

The basis of this research is a theoretical model of movement, illustrated in Figure 2.2. This model is an extended version of the conceptual framework introduced in Nathan et al. (2008). The model was originally proposed for movement ecology, in order to explore the causes, mechanisms, and patterns of movements of organisms (Nathan et al., 2008).

The model is composed of four major components, including (a) internal state; (b) movement characteristics; (c) movement path; and (d) external factors (Fig- ure 2.2). The first three components are related to the focal individual (i.e. the moving object under study). The latter is related to the environment within which the movement takes place. The focal individual is specified by the object’s particular intrinsic physical and behavioral movement properties.

Internal state: The internal state of the individual is denoted by its physiological and, where appropriate, its psychological specifications such as the motiva- tion of an individual for movement activity, readiness to move, and ability to execute and orient its movement.

Movement characteristics: In the original version of this model by Nathan et al. (2008) the movement characteristics are divided into motion capacity and navigation capacity, which are related to the focal individual. Simi- larly, here the movement characteristics encompass both capacities, where appropriate, as well as positional and temporal information of movement, and the physical movement parameters of the individual. These parameters can be derived from the trajectory of the focal object or can be captured directly from sensors.

Movement path: The movement process generates a movement path, which can take two forms: Namely, continuous path (i.e. curvilinear path), exemplified by the trajectory of a hurricane or a pedestrian, and discontinuous path (i.e. steps) with a series of stops-and-moves (e.g. saccadic movement of eyes, trajectory of a butterfly or a bee between flowers). In the original framework, the movement path is considered as a product of movement. Here, we take it as one of the principal elements of the movement model, since for some objects the movement path is constrained and predefined by the geographic context such as the road network or barriers (e.g. rivers). External factors: The external factors represent the surrounding environment

and the context of the movement activity as well as factors constraining or triggering the movement (e.g. spatial constraints, barriers, and attractions, weather condition etc.).

The relationships between the four components are shown with arrows in Figure 2.2. The arrows indicate the direction of influence of the components on each other. The movement process is performed when the individual is triggered by an internal motivation (i.e. readiness to start an activity). However, the external factors affect the way the individual performs the movement process (i.e. move- ment behavior). And finally, the movement characteristics of the individual have an impact on the geometry of the movement path.

The scope of this research extends over those aspects of the focal individual that are related to its movement characteristics and movement path. The main focus is on movement parameters and the patterns of their variation over time. This research mainly deals with the continuous type of movement paths. However, a comparison between movement characteristics of objects generating the two different forms of movement paths is carried out in the second stage of this thesis, which is presented in Research Paper 2 (page 97). In this thesis, the trajectory approach is employed in order to represent the continuous movement path of objects 2.1.

Formal Sciences (Mathematics, Statistics, Computer Science, etc.)

Social

Sciences CognitiveSciences Natural Sciences

(Geography, Biology, Environmental Science, etc.)

GIScience Computer _Science

Movement Research

Figure 2.3: Movement is a multidisciplinary research area