Geographic Information Systems GIS Analysis and Modeling

5. (9) Spread Functions ► An evaluation of phenomena that accumulate with distance ► It calculates the running total of a variable at each step when moving outwards at all directions from one ore more starting points, and writes the running total to an accumulation file ► Friction surface or Terrain trafficability

The calculation of distance using a spread function

The calculation of distance with barriers

Land use data layer Friction surface Generation of a travel-time data layer

► Travel time calculation Start point data layer Friction surface data layer Cumulative travel time data layer

► Travel-time analysis procedure - A spread function is used to calculate a travel-time map from the friction surface and the start points Friction surface data layer Start points data layer Travel time map

Least-Cost Analysis: Path 2 Distance between stops: Athens to Lathouriza: About 25km or 15.5mi Lathouriza to Thorikos: About 36km or 22mi Thorikos to Sounion: 13km or 8mi Total: 74km or 45.5mi From Erin Warford..

5. (10) Stream Functions ► The stream function (also termed a seek function) performs a directed search outward, step by step, from a starting point based on a set of decision rules. The procedure stops when the rules are violated ► The output is a trace of paths

5. (10) Stream Functions ► Applications – use of a seek function to model flow path

Stream Functions ► Application – find path through a sewer system from point A to point B

Stream Functions ► Application – delineate watershed boundaries

5. (10) Viewshed Analysis ► The concept of viewshed: the delineation of areas that are viewable from a point

5. (10) Viewshed Analysis ► Data sources for viewshed analysis Topography Surface feature locations & heights of obstructions Viewer positions Targets (optional) Viewshed map showing areas visible from one or more viewing positions. Shaded areas are hidden from view

5. (10) Viewshed Analysis ► Viewing parameters - Maximum viewable line-of-sight distance - Location of viewing point - Vertical and horizontal angle of view - Viewing direction

► Viewing parameters

Viewshed The above maps show the results of analyses around Saddleback (left) and Old Blue (right) mountains. On the maps, green areas are visible from the location cited (shown in yellow), while gray areas are obstructed from view. The Appalachian Trail is shown in red.

► scenic lookouts M. Dolce, Buffalo State College

From Erin Warford

Viewshed esri

5. (11) Illumination and Perspective View ► Illumination - Mimic the effect of shining a light onto a 3-D surface - Create a shaded relief image - Illumination source has a defined position relative to the surface

5. (11) Illumination and Perspective View ► Perspective view - Creates a 3-D block diagram showing how surface appears from a defined position - Is useful in showing the 3-D context of features on a surface, such as a natural landscape

3-D Perspective

Bowling Green Z=10 J. Yan, SUNY Buffalo

A. Toy, SUNY BUffalo

2. (4) TINs

Color infrared composite of the IKONOS draped over the DEM as viewed from the west side of the study area to the east from an elevation of 10,000 m, Xichang, China Xu, University of Utah, Gong, UC-Berkeley

Readings ► Chapter 5,6,9,10

5. (11) Illumination and Perspective View GIS can combine map types and display them in realistic three- dimensional perspective views that convey information more effectively and to wider audiences than traditional, two- dimensional maps.