1. Lecture 22: Introduction to Terrain and Network Analysis ------Using GIS-- Introduction to GIS

2. Part 1. Terrain analysis ------Using GIS-- Introduction to GIS

3. Component of Arc GIS that allows for 3D visualization of vector features, raster surfaces and Triangulated Irregular Networks in 3 dimensions. Can show terrain as well other information extruded in the third dimension. ------Using GIS-- Introduction to GIS What is Arc Scene? SF Bay Area extruded my median income by zip code

4. TIN stands for Triangulated Irregular Network A TIN is a data structure that defines geographic space as a set of contiguous, non-overlapping triangles, which vary in size and angular proportion. Like grids, TINs are used to represent elevation surfaces, and can be created directly from files of elevation sample points, but with TINs these sample points are irregularly distributed. ------Using GIS-- Introduction to GIS Three Dimensional data — TIN

5. Note the triangular facets defined by points ------Using GIS-- Introduction to GIS Three Dimensional data — TIN

6. ------Using GIS-- Introduction to GIS Here is a simple TIN skeleton, without the facets painted

7. ------Using GIS-- Introduction to GIS TINs can be created from raster Digital Elevation Models or from mass points with elevation values. TINs

8. ------Using GIS-- Introduction to GIS TIN triangles vary in size with the complexity of the terrain; more complex terrain needs more smaller triangles, and hence more points When creating a TIN form a DEM, Arc GIS uses the maximum z tolerance algorithm to determine how many and which sample points to use for defining the triangles that will represent the surface TINs

9. ------Using GIS-- Introduction to GIS Maximim z tolerance: Compares estimated height (in temporary TIN) to the grid height (in DEM). The differences are called offsets. The user specifies a maximum z-tolerance value which the offsets cannot be greater than. Hence, a high z value allows for considerable error, meaning fewer points will be used, while a low z value allows very little error meaning more will be used. TINs

10. ------Using GIS-- Introduction to GIS Points are selected through an iterative process. First it constructs a candidate TIN, and for each triangle in the TIN it calculates the elevation difference of the grid cells bounded by it. If the cell with the largest difference to triangle is greater than the z tolerance, that point is flagged for addition to the TIN model. Hence, a new point is added. It goes through every triangle in this way and then recalculates a new triangulation using the new points in addition. This continues until all points are within the specified z tolerance. TINs

11. ------Using GIS-- Introduction to GIS The Z tolerance specifies how close to the raster accuracy it will be. TINs

12. ------Using GIS-- Introduction to GIS DEM to TIN

13. ------Using GIS-- Introduction to GIS Note how the result changes with the z value TINs Z= 50Z= 200

14. ------Using GIS-- Introduction to GIS Breaklines: another feature that TINs have besides triangular facets; these represent discontinuities or changes on the surface of the land, like streams and roads. TINs Note: these lines are part of the TIN, not another layer

15. ------Using GIS-- Introduction to GIS So now we know how points are chosen, but how does it choose to join points together into triangles? The most common method of joining points to form triangles is Delaunay triangulation; in this method, all points are connected to their nearest neighbors to form triangles and triangles are as equi-angular, or compact as possible This is done by radiating circum-circles; circles are scribed through three points and the computer tests to see if any points are inside, if no points inside, it makes a triangle How are TINs generated

16. ------Using GIS-- Introduction to GIS

17. ------Using GIS-- Introduction to GIS A TIN Shown from above

18. ------Using GIS-- Introduction to GIS TINs Shown in 3D

19. ------Using GIS-- Introduction to GIS 3D TINs vs. 3D grids TIN’s facet resolution can be controlled in Arc View—the smaller the facets, the better the resolution

20. ------Using GIS-- Introduction to GIS Using Arc Scene Vector building footprints over a TIN, using elevation to define the bases of the buildings and number of stories to extrude them

21. ------Using GIS-- Introduction to GIS Using Arc Scene Here we overlay roads and urban areas on a DEM

22. ------Using GIS-- Introduction to GIS Using Arc Scene We can also create animations of fly throughs in ArcScene Click here Click here to see an animation created in Arc Scene.

23. ------Using GIS-- Introduction to GIS Steepest Path Another feature in Arc Scene is generation of a steepest path on a terrain surface

24. ------Using GIS-- Introduction to GIS The latest in 3d visualization Seehttp://www.visualizationsoftware.com/3dem/gallery.html For both movies and incredible 3 terrain renderings.

25. ------Using GIS-- Introduction to GIS Source : http://www.visualizationsoftware.com/3dem/gallery.htmlhttp://www.visualizationsoftware.com/3dem/gallery.html

26. ------Using GIS-- Introduction to GIS Source : http://www.visualizationsoftware.com/3dem/gallery.htmlhttp://www.visualizationsoftware.com/3dem/gallery.html

27. Part 2. Network analysis ------Using GIS-- Introduction to GIS

28. Network Analysis Networks defined as a set of interconnected line entities, generally arcs, whose attributes share some common theme primarily related to flow. Arcs in a network must share the attributes necessary for analyzing these flows (speed limits, frictions, etc.) ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

29. Network Arcs Can Have Direction Directed - flows allowed to move in a single direction (down stream, one way street) Undirected - flows allowed in both directions (two way streets) ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

30. A network is a system of linear features connected at intersections and interchanges. These intersections and interchanges are called nodes Arc Node ------Using GIS-- Introduction to GIS Basic elements of a network Adapted from UC Berkeley GIS Center The linear feature connecting any given pair of nodes is called an arc.

31. Network Attributes of interest Attributes that can be attached to a network: –origin, destination coordinates –shape point coordinates –street name/highway number –aliases on street name –directionality: one way traffic? –classification: freeway, arterial, collector, residential –speed limit, congestion (impedance) or travel time –traffic volume –length: driven length vs digitized length –scenic value –connectivity (turn tables) ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

32. Network Problems Path finding paths tours Allocation supply and demand impedance Spatial interaction accessibility interaction ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

33. Path finding Finding the shortest or least-cost manner in which to visit a series of locations in a network. The cost may be determined by distance or by travel-time or a combination of factors calculated as a cost value. Distance that factors in things that slow you down is known as functional distance Often the parameter that is minimized in path finding is travel time. This factors in things like topography, traffic volume, average speed, stops etc. ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

34. Computing best routes at the continental scale (e.g. how do I get from LA to New York?) is easy, because small variations in distance measures are relatively unimportant. At the intra-city level, the optimization criterion is travel time, which depends on legal restrictions (stop signs, traffic signals, one ways) and congestion (which varies by the minute), hence the margin of uncertainty in routing is far greater. ------Using GIS-- Introduction to GIS Path finding Adapted from UC Berkeley GIS Center

35. This would not happen if Ponch and John had Path finding software ------Using GIS-- Introduction to GIS “Ponch, there’s a 4-12 going on at the video arcade, what’s the fastest way to get there?” “Gee, I dunno John, let’s get off our bikes so we can look at our big, cumbersome map, and try to figure it out?”

36. Location - Allocation Allocation assigns portions of a network to a location based on predetermined criteria. Essentially an area of the network is assigned to be serviced or served by a facility at a given location. It is based on Supply, Demand, and Impedance. ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

37. Allocation Assigns Portions of a Network to a Center ------Using GIS-- Introduction to GIS These street segments can be used to define a service area Adapted from UC Berkeley GIS Center

38. Allocation Assigns Portions of a Network to a Center ------Using GIS-- Introduction to GIS Source: http://www.geo.umass.edu/courses/geo594a/warmup/warmup3/ Allocation analysis yields service areas for each of these facilities: that is, the areas they can reach within a specified driving time.

39. Allocation ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

40. Spatial interaction Accessibility = How Connected is a Node Accessibility is an aggregate measure of how reachable a location is from other locations. ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

41. Accessibility ------Using GIS-- Introduction to GIS Adapted from UC Berkeley GIS Center

42. Usefulness of Network Analysis Used by retailers in market studies for siting new facilities Used by utility company in managing their infrastructure: water, sewer, power Used by consumers to get directions Used by agencies to map out service areas: fire, police, public transportation facilities. ------Using GIS-- Introduction to GIS