Chacoan great houses have been described as providing "ritual" or "integrative" venues and as "monumental" in scale and in the amount of labor required for their construction. This study takes the approach that part of the function of community, monumental, or ritual structures is to transmit meaning and that an examination of visibility connections between these structures and small habitation sites in the surrounding community may provide information about the role of these messages in daily practice. Survey data from the Chacoan community at Kin Bineola, New Mexico is analyzed in a GIS environment using a model of visibility and distance developed for this project. The results show that, contrary to expectations, the great house is much less visible than a less monumental "Chacoan structure." Shrines, small structures interpreted as having a ritual function, are by far the most visible, suggesting a more complex relationship between monumentality and visibility.

A Geographic Information System (GIS) viewshed is the result of a function that determines, given a terrain model, which areas on a map can be seen from a given point(s), line or area. In the communications industry, this function has been used to model radio wave coverages and to site transceiver towers for cellular phones. However, there are errors involved with this function and, without the requisite data, it cannot account for building heights that may affect visibility in urban areas. This paper examines the ability to accurately show line-of-sight (LOS) radio wave coverages in order to establish the viability of replacing existing field methods with GIS viewshed analysis. An origin point capable of supporting a line-of-sight radio wave transmitter was chosen from within the Virginia Tech campus study area. A viewshed analysis was performed with ESRI's ArcView GIS, using this site as the observation point and a 30-meter resolution Digital Elevation Model (DEM) from the US Geological Survey. To check the accuracy of the viewshed, we transmitted at 27.5 GHz, a LOS frequency that has properties common in the wireless telecommunications industry. We also transmitted at 900 MHz from the same point to provide a comparison of the 27.5 GHz frequency to a non-line-of-sight radio wave.The data was recorded and then entered into the GIS where the visibility attribute of each point was compared to the viewshed's prediction of visibility. After this comparison, footprints and heights of campus buildings were included in the model, by adding them to the ground heights of the DEM. Another viewshed analysis was performed using the same origin site and the new building height DEM as the elevation grid. This second viewshed was compared with the recorded visibility attribute and signal strength data. The use of more complete surface data was shown to have a more positive correlation with the recorded data than the previous model. The comparison of these two viewsheds demonstrated how well the viewshed function can represent real-world visibility and showed that the accuracy of the viewshed function is dependent on the accuracy of the elevation model. The signal strength attribute enabled us to create a communications viewshed, or 'commshed'. The commshed consists of all data points that received a signal strong enough to carry data. The building viewshed and commshed were then compared to see to what degree the 27.5 GHz frequency deviates from true line-of-sight paths. There were slightly fewer points in the commshed than points 'in view' in the viewshed model due to the frequency's small wavelength and the lack of vegetation data in the elevation grid. However, when a power margin is added to the transmitter strength in order to overcome unpredictable conditions, the commshed's predictive accuracy increases as well. This means that for LOS radio systems running under normal operating conditions, the viewshed is an excellent predictor of receiving areas. A 900 MHz commshed was also created so that we could study the relationship between a line-of-sight radio wave and a wave that is not blocked by structures. This comparison showed that, as expected, a viewshed is a better predictor of LOS radio waves than non-LOS waves. The data sets and analysis presented here should help communications companies ascertain the best way to incorporate GIS and the viewshed function into their wave coverage mapping and tower siting processes. / Master of Science

Denna avhandling studerar befästningar i deras landskapssammanhang. Den undersöker vilka faktorer som bidragit till byggandet av befästningar, var de finns och förhållandet mellan bosättning och befästningar. Fokus ligger på stadsborgen från 1600-talet e.Kr. Jönköping, Kristianstad och Göteborgs samt förhistoriska befästningar i Jönköpings och Skåne län samt Göteborgs kommun. Litteraturstudier, kartstudier, Geografiska Informationssystem (GIS) och fältbesök används för att sätta befästningarna i ett sammanhang. Visuella analyser (Viewshed) skapas för att ytterligare visualisera befästningarna i deras landskapsmiljö och för att bedöma de faktorer som bidrar till deras konstruktion och förhållande till bebyggelse. Resultaten visar att det finns många olika faktorer som påverkar placering och konstruktion av befästningar. Befästningslinjer, försvarsbarhet, tillgång till vatten, hur attacker genomförs, kommunikativa-social-politiska-ekonomiska-religiösa och landskapsfaktorer kan alla ha spelat en roll i motiveringen för befästningsbyggandet. Det finns möjligen fler faktorer som påverkar läget. Ett absolut svar kanske inte är möjligt eftersom vi inte kan redogöra för de otaliga effekterna i det förflutna. Resultaten indikerar också att även om det finns tydliga kopplingar mellan 1600-talets stadsfort och deras tillhörande bebyggelse, finns det inget tydligt samband mellan de förhistoriska befästningarna och bebyggelsen i fråga. Förhistoriska ringfort sticker ut eftersom det finns tydliga tecken på bosättningsaktivitet på två av platserna som ingår i denna studie. En skarp kontrast uppstår mellan ringborgen och de andra förhistoriska befästningarna som beaktas i denna studie, eftersom endast en plats har säkra bevis för bosättningsverksamhet inom sig när man betraktar bergsborgen. Det är uppenbart att endast detaljerad utgrävning och undersökning kommer att kunna belysa om bosättningsverksamhet förekom vid förhistoriska befästningar (Bergsfortifikationer/Ringfort), och riktade studier kan också kunna utöka vår förståelse av deras exakta funktion och motivationen bakom deras landskapspositionering. Den siktbaserade analysen tyder på att de bebyggelser som kan vara samtida med de förhistoriska befästningarna har ett lågt rumsligt förhållande till forten. Dessutom verkar det som om sikten på vissa platser kanske inte har varit den huvudsakliga faktorn för platsernas placering i landskapet, och på vissa platser verkar potentialen för kontroll över en betydande kommunikationsväg vara inflytelserik för platsplaceringen.

Traditional viewshed analyses distinguish between those areas which can be seen from a given observation point and those which cannot be seen. Given a surface digital elevation model (DEM) and observer properties (location and height), the algorithm computes whether or not each target cell is within the observer's line-of-sight. Just as significant and robust (although yet not commercially available) would be a tool that could search local neighborhoods of the observer to determine if different tower placements could achieve significantly improved viewsheds. This thesis customizes the popular ArcGIS software to demonstrate the implementation of such a tool. The use of different sampling methods specifies locations to site observation points throughout the Virginia Tech central campus, characterized by having large open areas in an otherwise urban environment. Analysis of the viewsheds calculated both before and after applying the optimization tool determined the amount of coverage gained by moving the observer short distances across the ground. In large open areas (Drillfield, parking lots), optimization achieved minimal gain, however in areas near buildings, significant increases in visible area were possible by moving the observer to the top of a nearby building. This research rejects the common belief that the best location for an observer or transmitter in open areas is always at the highest elevation point. However, in settings with tremendous vertical differences over small horizontal distances (ground to roof), the belief is justified. / Master of Science

Digital Elevation Models (DEMs) are computer-generated representations of the earth's surface. These surfaces can be used to predicted Line-of-Sight (LOS) radio propagation. DEM resolution can affect the results of this prediction. This study examines the effect of DEM resolution on accuracy by comparing varied resolution terrain data for a portion of Blacksburg, Virginia using the prediction of ESRI's ArcView® viewshed algorithm. Results show that resolutions between one-meter and thirty-meters have little effect on the aggregate accuracy of the viewshed. / Master of Science

Viewshed refers to the calculation and visualisation of what part of a terrain isvisible from a given observer point. It is used within many fields, such as militaryplanning or telecommunication tower placement. So far, no general fast methodsexist for calculating the viewshed for multiple observers that may for instancerepresent a road within the terrain. Additionally, if the terrain contains over-lapping structures such as man-made constructions like bridges, most currentviewshed algorithms fail. This report describes two novel methods for viewshedcalculation using multiple observers for terrain that may contain overlappingstructures. The methods have been developed at Vricon in Linköping as a Mas-ter’s Thesis project. Both methods are implemented using the graphics program-ming unit and the OpenGL graphics library, using a computer graphics approach.Results are presented in the form of figures and images, as well as running timetables using two different test setups. Lastly, future possible improvements arealso discussed. The results show that the first method is a viable real-time solu-tion and that the second method requires some additional work.

No description available.

This thesis presents an interdisciplinary examination of a series of towers existing between the sites of Kastro Kallithea and New Halos along the north ridge of Greeces Othrys Mountains. The overarching goal is to utilize digital archaeological techniques such as GIS to refine the methodologies used in determining the rate of efficient communication between towers in defense networks. Tools within the ArcGIS software package allow line of sight and viewsheds to be examined remotely with a series of criteria to be met, such as maximum allowable distance. In doing so, past studies of regional networks are critiqued in light of their inclusion or exclusion of considerations such as distance, atmospheric conditions, and time of day when determining over how far a distance fire signaling could be effective. A second critique explores the dangers of employing digital means from the perspectives of both the investigator and public. / History and Classics

The Global Positioning System (GPS) has recently become the significant mapping tool for millions of customers worldwide, providing its users with accurate terrestrial positions almost instantaneously. The functionality of a GPS receiver depends on the number of satellites to which it can establish an unobstructed line of sight. Current satellite availability prediction tools perform satellite visibility predictions without considering terrain or structures that block GPS signals, a major issue in mountainous and urban areas. This paper describes a new Geographic Information Systems (GIS) tool, a customization of ArcGIS named Satellite Viewsheds, which predicts satellite visibility for any place and time while considering line of sight obstructions. Satellite Viewsheds requires a raster surface model, the test date and time, and the orbital properties of the satellites. It produces grids depicting the number of visible satellites and optimal viewing time for every cell in the grid. Satellite Viewsheds allows users to avoid areas of signal loss and choose the best time to map using their GPS receivers. The field test of Satellite Viewsheds proved that the tool performs satellite visibility predictions consistently and accurately. The research outlined in this paper indicates that Satellite Viewsheds is the first tool of its kind. / Master of Science

The analysis of visibility between two points on the earth's terrain is a common use of GIS software. Most commercial GIS software packages include the ability to generate a viewshed, or a map of terrain surrounding a particular location that would be visible to an observer. Viewsheds are often generated using "bare-earth" Digital Elevation Models (DEMs) derived from the process of photogrammetry. More detailed models, known as Digital Surface Models (DSMs), are often generated using Light Detection and Ranging (LIDAR) which uses an airborne laser to scan the terrain. In addition to having greater accuracy than photogrammetric DEMs, LIDAR DSMs include surface features such as buildings and trees. This project used a visibility algorithm to predict visibility between observer and target locations using both photogrammetric DEMs and LIDAR DSMs of varying resolution. A field survey of the locations was conducted to determine the accuracy of the visibility predictions and to gauge the extent to which the presence of surface features in the DSMs affected the accuracy. The use of different resolution terrain models allowed for the analysis of the relationship between accuracy and optimal grid size. Additionally, a series of visibility predictions were made using Monte Carlo methods to add random error to the terrain elevation to estimate the probability of a target's being visible. Finally, the LIDAR DSMs were used to determine the linear distance of terrain along the lines-of-sight between the observer and targets that were obscured by trees or bushes. A logistic regression was performed between that distance and the visibility of the target to determine the extent to which a greater amount of vegetation along the line-of-sight impacted the target's visibility. / Master of Science