@PHDTHESIS{Gottfried2005b,
  author = {Gottfried, Bj{\"o}rn},
  title = {Shape from Positional-Contrast: Characterising Sketches with Qualitative
	Line Arrangements},
  school = {Universit{\"a}t Bremen},
  year = {2005},
  address = {Bremen, Germany},
  abstract = {Graphical queries for the purpose of searching for pictorial information
	are of growing interest in areas where pictures provide valuable
	information, including, for instance, design, architecture, and engineering.
	Sketching graphical queries is a natural way of revealing the visual
	appearance of objects one has in mind. The problem which arises is
	identifying necessary shape properties of sketches, that is, those
	properties which are not accidental but are necessary for specifying
	a particular object property. This problem arises in particular because
	sketches are imprecise, and often distorted by the artistic limitations
	of the sketcher. From the theoretical point of view the concept of
	\textbackslashtextit{pictorial space} applies. In this context, new
	concepts are required, in particular for dealing with imprecise shape
	information in the plane. Taking into account constraints imposed
	by pictorial space, a relation algebra of intersection-free relations
	is proposed, which allows reasoning about qualitative line arrangements
	in the plane. The theory is further developed for characterising
	polygons, by deriving a number of qualitative properties which aid
	in describing polygons qualitatively. Applying this theory, only
	line arrangements which are both readily sketched and easily perceivable
	are considered to be different. The notion of positional-contrast
	is introduced, which points out that the particular arrangements
	of line segments, i.e. their positions relative to each other, provide
	an expressive means of characterising necessary shape properties.
	The method developed in this work is applied in using graphical queries
	to search for historical objects. Specifying objects graphically,
	it is shown that the new method is capable of dealing with imprecise
	sketches by describing necessary shape properties using qualitative
	line arrangements, i.e. by taking into account positional-contrast.
	Overall, the investigations which are carried out in this work pertain
	to the field of knowledge representation in artificial intelligence.
	The representation developed here sticks to ideas developed in the
	field of \textbackslashtextit{qualitative spatial reasoning} ---
	one of its principal goals being the representation of commonsense
	knowledge about the physical world. As is common practice in this
	field, knowledge about the domain in hand is made explicit in order
	to arrive at efficient reasoning methods. Here, we confine ourselves
	to a representation of shape information and make explicit knowledge
	about our object of research, namely about imprecise shape information
	in picture space.},
  owner = {pmania},
  timestamp = {2012.11.06},
  url = {http://www.tzi.de/~bjoerng/Gottfried2003a.pdf}
}