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Topic: Visibility graph analysis

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	Visibility Graph Analysis
		Visibility graph analysis is a spatial analysis technique for urban and building spaces pioneered at the VR Centre, which may also be applied to landscapes.
		VGA has led us to talk about "Visual Integration" (the analogue of axial integration), or "visual depth" (number of visibility turns from one location to another), or even "visual connectivity" (for "neighbourhood size", or the approximate isovist area, as in space syntax, "connectivity" is used to discuss the number of lines connected to another).
		Turner, A., Doxa, M., O'Sullivan, D. and Penn, A., 2001, From isovists to visibility graphs: a methodology for the analysis of architectural space.
	www.vr.ucl.ac.uk /research/vga (1995 words)

	Graph theory Summary
		Graphs with weights can be used to represent many different concepts; for example if the graph represents a road network, the weights could represent the length of each road.
		Definitions of graphs vary in style and substance, according to the level of abstraction that is approriate to a particular approach or application.
		Firstly, analysis to determine structural properties of a network, such as the distribution of vertex degrees and the diameter of the graph.
	www.bookrags.com /Graph_theory (3094 words)

	Visibility graph - Wikipedia, the free encyclopedia
		Visibility graphs are classically regarded as two dimensional artefacts.
		In addition to theoretical problems, visibility graphs also have practical uses, for example, to calculate the placement of radio antennas, or as a tool used within architecture and urban planning through visibility graph analysis.
		Visibility graphs are also used in mobile robotics as a (generally offline) path-planning tool when the geometry of the environment is known, although robots have been designed that collect isovist information as they explore the environment using ultrasound sensors, which can then be turned into a visibility graph of recognisable known locations.
	en.wikipedia.org /wiki/Visibility_graph (213 words)

	Visibility graph analysis - Wikipedia, the free encyclopedia
		Visibility graph analysis (VGA) is a method of analysing the inter-visibility connections within buildings or urban networks.
		Visibility graph analysis was developed from the architectural theory of space syntax by Turner et al (2001), and is applied through construction of a visibility graph within the open space of a plan.
		Visibility graph analysis uses various measures from the theory of small-world networks and centrality in network theory in order to assess perceptual qualities of space and the possible usage of it.
	en.wikipedia.org /wiki/Visibility_graph_analysis (144 words)

	Representative Visibility for Forest Service Class I Areas
		Visibility is expressed as Standard Visual Range (SVR) – the greatest distance at which an observer can just see a fl object viewed against the horizon sky.
		Visibility conditons worse (lower SVR) than the 10th percentile SVR occur on only 10% of days, or 90 % of days have better (higher SVR) visibility.Visibility conditions worse than the 50th percentile SVR occur half the days and, likewise, visibility conditions are better than the 50th percentile half the days.
		Visibility conditions are better than the 90th percentile on 10% of days and are worse on 90% of days.
	www.fs.fed.us /r6/aq/natarm/representative_svr.html (566 words)

	Graphs and graphical methods
		A graph is inherently more limited in precision than a table of numerical values or an analytic equation, but it can contribute a "feel'' for the behavior of data and functions that numerical tables and equations cannot.
		Most good graph papers are ruled in colors that are soft enough that they do not distract the viewer from the plotted lines and points, which are usually in fl.
		The legend should state what the graph is about, identify symbols.and line types used, and provide all needed information that will not be provided in the document to which the graph will be attached.
	www.chemistry.adelaide.edu.au /external/soc-rel/content/datagraph.htm (1496 words)

	Viewer
		This visibility list is passed to the viewer and defines the default display of structures when each group is viewed.
		The graphs drop down will contain a list of possible graphs that can be drawn based on the currently visible molecules.
		As the shape is moved all the equivalent data points within the structure view and graph views are highlighted to give an interactive paintbrush for the data.
	www.ebi.ac.uk /msd-srv/apps/Viewer/index.html (3327 words)

	Gamasutra - Features - "Game AI: The State of the Industry" [11.01.00]
		Terrain analysis takes the relatively simple task of path-finding across a map to its next logical step, which is to get the AI to recognize the strategic and tactical value of various terrain features such as hills, ridges, choke-points, and so on, and incorporate this knowledge into its planning.
		Visibility graphs are fairly simple constructs originally developed for the field of robotics motion.
		The visibility graph for this scene uses the vertices of the polygons for the vertices in the graph, and builds the edges of the graph between the vertices wherever there is a clear (unobstructed) path between the corresponding polygon vertices.
	www.gamasutra.com /features/20001101/woodcock_02.htm (1508 words)

	Introduction
		Unlike numerical analysis, where an algorithmic contribution is accompanied by the source code (in Fortran) and is kept in central databases, implemented geometric algorithms are not catalogued or, when offered to the community, are offered as stand-alone units rather than units building on the work of others.
		Whereas the discussion above about visibility problems in the plane was not concerned with a particular output device, one can partition the work done on visibility in space clearly to one of two categories depending on the stage at which we are concerned with the output device.
		Also, the advantage of using the visibility map rather than the SVBSP for shadow computation under a point light source is that it makes it possible to preserve the solids in the input because all adjacency information in the solids can be maintained after determining the shadows.
	www.cs.ualberta.ca /~ghali/thesis/node3.html (7094 words)

	SuperMemo: Learning statistics dialog
		For that reason, the initial value of the RF matrix is taken from the model of a less-than-average student (the model of average student is not used because the convergence from poorer student parameters upwards is faster than the convergence in the opposite direction).
		This graph is used by the SuperMemo Algorithm to quickly estimate the first value of A-Factor at the moment when all we know about an element is the first grade it has scored in its first repetition
		The first interval graph shows exponential regression curve that approximates the length of the first interval for different numbers of memory lapses (including the zero-lapses category that corresponds with newly memorized items).
	www.supermemo.com /archive/help2002/analysis.htm (1726 words)

	Graph Drawing
		The problem that graph drawing tries to tackle is how to represent a set of edges and vertices in such a way that it will convey the most meaning.
		Looking at the graph on the right, it is very hard to see that vertex 4 has so many connections and it is hard to tell that vertex 3 and 7 only have one vertex separating them and are therefor relatively close.
		In this step, the graph is converted from its mathematical representation (in this case V={1, 2, 3, 4, 5, 6} and E={(1,4), (1,5), (1,6), (2,4), (2,5), (2,6), (3,4), (3,5), (3,6)}) into a 2d drawing where the number of crossings are kept to a minimum.
	davis.wpi.edu /~matt/courses/graphs (2391 words)

	Visibility Analysis in the Umayri Region
		The first of these concerns the limited visibility at Tall al-Umayri and uses a GIS to reconstruct a system of watchtowers that would have functioned to expand Umayri's visual control of the surrounding landscape.
		If the target cell is visible the GIS places a "1" in that cell in the viewshed map, if it is not visible the GIS assigns a "0" to the cell.
		One of the most obvious applications of visibility analysis to Near Eastern archaeological material is the establishment of viewsheds for fortified sites.
	www.casa.arizona.edu /MPP/viewshed/vspaper.html (3944 words)

	Research Projects and Publications
		Topological analysis of a scalar function defined on the surface and its associated gradient field reveals the relationship between the features of interest and critical points of the scalar function.
		We prove tight upper and lower bounds on thenumber of loops in the Reeb graph that depend on the genus, the number of boundary components,and whether or not the 2-manifold is orientable.
		Visibility graphs of simple polygons have been characterized and there are algorithms that construct these graphs efficiently.
	graphics.cs.ucdavis.edu /~vijayn/research/research.html (1722 words)

	An Extended Data-Flow Architecture for Data Analysis and Visualization
		The challenge from the perspective of developing tools for data analysis and visualization based upon the data-flow paradigm is to preserve the virtues of such an approach while trying to minimize the inherent limitations embodied by the use of a naive "data-flow" execution model for the visual programs.
		Hence, the selection may be performed by a simple transformation of the graph: excising the Switch module altogether, and substituting arcs from the selected source (either Isosurface or MapToPlane) to each of the modules that, in the original network, received the result of the Switch module.
		Instead, the graph must be evaluated in stages: 1) determine the selection value, 2) determine the necessary input to the Switch module and 3) evaluate the remainder of the graph.
	www.research.ibm.com /dx/proceedings/dx_paper/index.htm (4865 words)

	Visibility and Shadows from a Point in Space
		In the rest of this chapter, we show how to represent and compute the visibility map from a point, how to use the visibility map to determine the shadow edges in a scene illuminated by a point light source, and how to refine the model to include these shadow boundaries.
		The set P represents the set of faces in the planar graph corresponding to the transparent view from the same viewpoint when the graph is embedded on the image plane and the hidden edges and vertices are eliminated.
		If the size of the visibility map is quadratic in the size of the input, the size of the model after inserting the shadow edges is quadratic in its size before the insertion.
	www.cs.ualberta.ca /~ghali/thesis/node11.html (4675 words)

	Robotics \| 2. Robot Navigation.
		The visibility graph method creates an exact model of the world (modified appropriately to reflect the fact that the robot is represented as a point) and checks line-of-sight between vertices on the map.
		The first required task was to build a visibility graph that would allow the robot to navigate around two 4 ft. x 4 ft. obstacles spaced 4 ft. apart, parallel to each other, representing the obstacles as continuous polygons.
		Since the graph is only constructed in terms of eight-connected squares, the robot's motion planning is in 45-degree increments.
	www.cs.swarthmore.edu /~apsheni1/cs82/web/lab2 (1705 words)

	Zoomgraph version 0
		A zoomable interface to large graphs. Zoomable means you can smoothly zoom in and out and easily move between nodes. It’s not exactly what you would expect and is a little hard to explain, you’ll have to try it.
		The graph that popped up represents a corporate communication network. Each node represents an employee (with a department property), and each edge represents communication between two employees (with a frequency property on the edge indicating the number of undirected communications).
		A basic export of a graph to a Pajek file. The default behavior is to save out all nodes and edges that are visible. To change this you can specify a query (this is a little broken).
	www.hpl.hp.com /research/idl/projects/graphs/doc/zg-manual.html (3957 words)

	JOT: Journal of Object Technology - Class-based Visibility from an MDA Perspective: From Access Graphs to Eiffel, M. ...
		Eiffel visibility principles enlarge the range of potential visibility use, by letting a class propose different “interfaces” based on the application semantics.
		Considering visibility in the framework of MDA demands, as for other object orientation concepts, to clarify what is visibility independently from specificities of target programming languages.
		Our proposal is twofold: first we introduce a language-independent visibility model which has a graphical counterpart easy to integrate into UML (access graphs); then, on the basis of the philosophy of the MDA approach, tools that automate visibility model transformations are developed.
	www.jot.fm /issues/issue_2004_04/article10 (4873 words)

	School of Computing, Queen's University (Site not responding. Last check: 2007-11-05)
		Computational geometry, the design and analysis of combinatorial algorithms for geometric problems, is currently at the forefront in the design and development of computer software for geometric intensive applications.
		Rappaport is focusing on the structure of visibility graphs, as it may apply to graph drawing.
		A combinatorial description of a graph, perhaps with some incomplete geometric information, is given as input, and a readable drawing of the graph is to be produced as output.
	www.cs.queensu.ca /researchreport/faculty/rappaport.html (428 words)

	Amazon.com: Drawing Graphs: Methods and Models (Lecture Notes in Computer Science): Books: M. Kaufmann,D. ... (Site not responding. Last check: 2007-11-05)
		Graph drawing comprises all aspects of visualizing structural relations between objects.
		Gives a systematic overview of graph drawing and introduces the reader gently to the state of the art in the area.
		Graph drawing has emerged in recent years as a very lively area in computer science.
	www.amazon.com /Drawing-Graphs-Methods-Lecture-Computer/dp/3540420622 (1070 words)

	XGRAPH General Purpose 2D Graphing Utility
		A 'soft' range means that the graph will be drawn out to that range even if your data does not span that range, but if data exists outside that range, the range will be extended to include the data.
		Often it is helpful to add a line to your graph, perhaps to better point at something you are annotating, or to show a critical region on your graph.
		It is often useful to re-position the boundaries of the graph on the screen or printed-page, to allow more space for axis label names, or textual notes and explanations around the graph.
	www.xgraph.org (7109 words)

	Exploring isovist-based correlates of spatial behavior and experience
		Isovist and visibility graph analysis offer the great chance to describe spatial properties of environments generically.
		Therefore, the exploratory spatial analysis concentrated on the translation of qualitative classic theories from environmental psychology (e.g., information rate, prospect and refuge) into concrete isovist measurands.
		One approach evaluated a single isovist from a central position within the environment, the other approach combined aspects of visibility-graph analysis and isovi st analysis by evaluating and averaging over isovist measurands derived on a regular grid.
	www.kyb.mpg.de /publication.html?publ=2994 (405 words)

	Gamasutra Printer Friendly Article
		Terrain analysis is a much tougher problem than simple pathfinding in that the AI must study the terrain and look for various natural features -- choke-points, ambush locations, and the like.
		Good terrain analysis can provide a game's AI with multiple "resolutions" of information about the game map that are well tuned for solving complex pathfinding problems.
		The developers used a visibility graph (see "Visibility Graphs" sidebar) to break down the game's terrain into distinct but interconnected areas; the AI can then use these larger areas for higher-level pathfinding and vehicle direction.
	www.gamasutra.com /features/20001101/woodcock_pfv.htm (3682 words)

	Problem Set 4 (Site not responding. Last check: 2007-11-05)
		Free space is defined as the complement of P. The visibility graph of P is defined as the graph whose nodes are the vertices of P, and whose edges join pairs of nodes for which the corresponding segment lies in free space.
		However, in typical cases, the number of edges in the visibility graph is often closer to O(n).
		which, given a graph and a vertex in the graph, returns a list of vertices that can be reached from the vertex by traversing a single edge in the graph.
	www.cs.dartmouth.edu /brd/Teaching/AI/Homeworks/DFA/ps4.html (3463 words)

	Quality Analysis Methodology
		The quality analysis comparison performed between CineForm's 10-bit Visually Perfect codec and the DVCPRO HD codec was performed at CineForm's facilities by CineForm employees.
		PSNR analysis uses a standard mathematical model to measure an objective difference between two images.
		It is commonly used in the development and analysis of compression algorithms, and for comparing visual quality between different compression systems.
	www.cineform.com /technology/HDQualityAnalysis10bit/HDmethodology10bit.htm (625 words)

	SuperMemo: Learning statistics dialog
		This graph is used to compute the estimated forgetting index that in turn is used to normalize grades (for delayed or advanced repetitions) and estimate the new value of item's A-Factor.
		To zoom in on a portion of the graph (as in pictures below), sweep the portions of the graphs that are to be removed with the mouse (e.g.
		The period shown on the graph spans from Sep 11, 2002 to Jan 3, 2003.
	www.supermemo.com /help/analysis.htm (2069 words)

	Research Projects and Publications
		Topological analysis of a scalar function defined on the surface and its associated gradient field reveals the relationship between the features of interest and critical points of the scalar function.
		We prove tight upper and lower bounds on thenumber of loops in the Reeb graph that depend on the genus, the number of boundary components,and whether or not the 2-manifold is orientable.
		Visibility graphs of simple polygons have been characterized and there are algorithms that construct these graphs efficiently.
	graphics.idav.ucdavis.edu /~vijayn/research/research.html (1722 words)

	2006 Air Pollution Events - Texas Commission on Environmental Quality - www.tceq.state.tx.us
		Analysis of satellite imagery, wind flow, and PM2.5 regional patterns indicates that much of the PM2.5 observed on March 14 and 15 was probably smoke from agricultural burning in southeastern Mexico and Central America.
		In contrast, the PM2.5 on March 16 and 17 appears to be primarily from sources in the U.S. On March 16 and 17, winds were from the northeast, bringing in continental air from the midwestern U.S., and wind speeds were very light.
		Visibility is affected by the particulate levels and by the relative humidity.
	www.tceq.state.tx.us /assets/public/compliance/monops/air/sigevents/02/event2002-03-14ctx.html (335 words)

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