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Copy file name to clipboardExpand all lines: introduction.tex
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% GIS research
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The core of the research carried out in this thesis is concerned with \emph{geographic information systems (GIS)}, which produces tools to create, manipulate, analyse and visualise the digital objects that are inherent in these abstract representations of the world.
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The core of the research carried out in this thesis is concerned with \emph{geographic information systems (GIS)}\footnote{Within this thesis, I always use `GIS' and not `GISs'.
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This is partly because of aesthetics (GISs reads badly and hears worse), but also because I would argue that current GIS are not really systems but disparate collections of methods, tools and processes.
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As such, when I write about GIS I rarely refer to systems and most often use the word as a modifier rather than a noun.}, which produces tools to create, manipulate, analyse and visualise the digital objects that are inherent in these abstract representations of the world.
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Compared to other software categories that also allow us to model and manipulate objects that are represented geometrically, such as those used in computer-aided design (CAD) and geometric modelling, GIS tools stand out as being \emph{remarkably generic} \citep{Coppock91,Gold06}.
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GIS are used equally to manually build objects by applying interactive drawing operations, to semi-automatically create full models from raw acquired data, to manage large collections of heterogeneous datasets and keep them up to date, or as interactive point-and-click environments to query the attributes of and perform simple calculations on existing datasets.
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Because of this genericity, GIS are expected to support a large number of different data formats from multiple sources and a wide variety of operations---all while solving problems in a mix of 2D and 3D and preserving the key characteristics of sometimes mutually incompatible computer representations.
Copy file name to clipboardExpand all lines: math.tex
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While the study of set theory only formally started with \citet{Cantor74}, its intuitive and minimal concepts were later used in order to give a foundation to almost all areas of mathematics\footnote{Even as some mathematicians and philosophers have argued against set theory as a foundation for all of mathematics.}.
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Since the basic concepts of set theory are used in this thesis in order to describe many other concepts, this section gives a very short primer using the same notation that is used in this thesis.
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However, it is worth noting that the descriptions used here are reflect the concepts generally used in GIS, and so are meant to be intuitive and not very formal.
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Perhaps more importantly, these definitions do not reflect modern mathematical thought on the topic\footnote{In short, this intuitive definition of sets pretty much assumes that anything can be put into a set without leading to paradoxes, which is not the case.}, which is much more precise but is much less accessible, \eg\ axiomatic set theory.
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Perhaps more importantly, these definitions do not reflect modern mathematical thought on the topic\footnote{In short, these intuitive definitions pretty much assume that anything can be put into a set without leading to paradoxes, which formally is not the case.}, which is much more precise but also less accessible, \eg\ axiomatic set theory.
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Set theory starts by considering the existence of a given domain of objects from which one may build sets, which is known as the \emph{universe set} and denoted as $\mathbb{U}$.
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These objects can be anything, including other sets.
\caption[Two rectangles and two points defined as point sets]{The rectangle $\mathbb{A}$ is represented by the set of points where $1\leq x \leq4$ and $1\leq y \leq3$. In more compact (set builder) notation, $\mathbb{A} = \left\{ (x,y) \middle| x \in [1,4] \wedge y \in [1,3] \right\}$.
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For the other objects, rectangle $\mathbb{B} = \left\{ (x,y) \middle| x \in [2,3] \wedge y \in [1,2] \right\}$, point $a \in\mathbb{A}$, point $b \in\mathbb{B}$ and point $b \in\mathbb{A}$.
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$\mathbb{B}$ is a subset of $\mathbb{A}$ ($\mathbb{B} \subset\mathbb{A}$).
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$\mathbb{B}$ is a subset of $\mathbb{A}$ (\ie\ $\mathbb{B} \subset\mathbb{A}$).
\caption[An annulus partitions the Euclidean plane into three parts]{An annulus with boundary partitions the Euclidean plane into three parts: its interior (yellow), its boundary (black) and its exterior (white). Note that none of these necessarily have to be connected.}
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\caption[An annulus partitions the Euclidean plane into three parts]{An annulus with boundary partitions the Euclidean plane into three parts: its interior (yellow), its boundary (black) and its exterior (the rest of this page).
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Note that none of these necessarily have to be connected.}
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\label{fig:annulus}
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}
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The \emph{interior} of a point set $\mathbb{S}$ consists of all points where there exists an open ball centred at them such that all the points in the ball are in $\mathbb{S}$, the boundary of $\mathbb{S}$ consists of the points where all possible open balls centred at them have points in $\mathbb{S}$ and out of $\mathbb{S}$, and the exterior of $\mathbb{S}$ consists of all points where there exists an open ball centred at them such that all the points in the ball are out of $\mathbb{S}$.
Once objects are defined as sets of points, point-set topology works with functions that relate these sets to each other.
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A function from one point set to another is said to be \emph{continuous} if the preimage (\ie\ the inverse image) of every open set is open.
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If a function is continuous and its inverse function is also continuous, it is known as a \emph{homeomorphism}.
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When such a function exists between two point sets, they are said to be \emph{homeomorphic} or, more informally, \emph{topologically equivalent}, such as the two objects shown in \reffig{fig:homeomorphism}\footnote{Related to the joke: `A topologist is a mathematician who can't tell the difference between a coffee mug and a donut'.}.
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When such a function exists between two point sets, they are said to be \emph{homeomorphic} or, more informally, \emph{topologically equivalent}, such as the two objects shown in \reffig{fig:homeomorphism}.
\caption[A coffee mug and a donut are homeomorphic]{A coffee mug and a donut are homeomorphic. Intuitively, this can be known as it is possible to deform one into the other. The mug was rendered from the model at \url{http://www.thingiverse.com/thing:7953}.}
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\caption[A coffee mug and a donut are homeomorphic]{A coffee mug and a donut are homeomorphic\footnotemark. Intuitively, this can be known as it is possible to deform one into the other. The mug was rendered from the model at \url{http://www.thingiverse.com/thing:7953}.}
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\label{fig:homeomorphism}
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\end{figure}
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\footnotetext{Related to the joke: `A topologist is a mathematician who can't tell the difference between a coffee mug and a donut'.}
More formally, a simplicial complex can be defined as a collection of simplices such that:
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\begin{itemize}
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\item
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Every face of a simplex is also in the simplicial complex
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every face of a simplex is also in the simplicial complex;
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\item
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The intersection of any two simplices is either empty or is a common face of both of them\footnote{Note that this implies a definition where a simplex contains its boundary.}
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the intersection of any two simplices is either empty or is a common face of both of them\footnote{Note that this implies a definition where a simplex contains its boundary.}.
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\end{itemize}
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Based on the set of common vertices shared by two simplices, it is possible to define certain \emph{topological relationships} between them.
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