Adding the Z Introduction • Introduction to 3D Visualization • Introduction to 3D Analyst • Navigating a 3D Scene • Saving a Scene as an Image • Using the Viewer Control Bar • Setting 3D Scene Properties Introduction to 3D Visualization To date, we've used ArcView to examine our world in 2 dimensions. The images we've manipulated have appeared on a flat screen or paper. While the images will continue to be communicated using these mediums, this lecture introduces a tool that enables us to add a third dimension to the maps we create. We experience the world in 3D, and now we will make maps (and models) that look more like the places we seek to represent. By adding a third dimension, we will likely observe new and interesting patterns in our data, thus enhancing our ability to analyze the problem at hand. Introduction to 3D Analyst3D Analyst is an ArcView extension that displays spatial data in 3D perspective. It lets you examine data from different angles and perspectives. Before we get started, let's review some concepts from Lectures 13a* and 13b*. SURFACE MODELS A surface model represents a spatial phenomenon that can be measured continuously over some part of the earth. Terrain elevation surfaces are probably the most common example--common enough to have their own acronyms (DEM for Digital Elevation Model or DTM for Digital Terrain Model). Whatever the quantity represented, the model will be a generalization of reality. Often a number of different models of the same area are used to solve a problem. For example, the best location to locate a cabin may depend on factors like slope, exposure to sunlight, and vegetation. GRID AND TIN DATA STRUCTURES A grid partitions geographic space into a matrix of identically-sized square cells, each of which stores a numeric value. Values from sample data points are interpolated to create a continuous surface. A TIN (Triangulated Irregular Network) 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 surfaces such as elevation, and can be created directly from files of sample points. The TIN is defined by two elements: a set of input points with x, y, and z values, and a series of edges connecting these points to form triangles. Each input point becomes the node of a triangle in the TIN structure, and the output is a continuous faceted surface of triangles. The triangles are constructed according to a mathematical technique called Delaunay triangulation. The technique guarantees that a circle drawn through the three nodes of any triangle will contain no other input point, as shown below. The elevation value for any location on a TIN surface can be interpolated using the x, y, * Kindly refer to the Lecture Notes sectionand z values of the bounding triangle's nodes. Additional information, like slope, aspect, and surface area, can be calculated for each triangle face. DEMONSTRATION Now, let's introduce two new concepts: the 3D Shapefile and the 3D Scene. 3D SHAPEFILE To date, we've worked with 2D shapefiles and coverages. Now, we're adding the Z! To display features (like buildings, rivers, and streets) found on or beneath surfaces, 3D Analyst makes use of the 3D shapefile. Ordinary 2D shapefiles can easily be converted to 3D, and 3D Analyst can display 2D shapefiles in 3D on the fly. A 3D shape is a point, line, or polygon which (in addition to its x, y coordinates) stores a z coordinate (representing its elevation) as part of its geometry. A point has one z coordinate; lines and polygons have one z coordinate for each vertex in the shape. The graphic below shows the theme table of a 2D point shapefile, with the x, y coordinates of every point. The bottom graphic shows 3D shapefile with its x, y and z coordinates. As shown below, the shape of the 3D shapefile is called PointZ. The terminal "Z" identifies it as a 3D shapefile.DEMONSTRATION 3D SCENE A great deal of the surface creation, editing, and analysis is done in a View document. To display data in three dimensions, 3D Analyst uses a new document type: the 3D scene. A 3D scene is a three-dimensional viewing environment for spatial data. Like a View window, a 3D scene consists of a Table of Contents and a display area. The display area is called a "viewer." The main difference between a 3D scene and a view is that a 3D scene lets you see your data in three-dimensional perspective, from any horizontal and vertical angle you like. A 3D scene can have multiple viewers to look at the same data in several windows simultaneously, with each window set to a different perspective. Navigating a 3D Scene Navigation allows you to control the perspective of a 3D scene by rotating, zooming, and panning. All three operations are performed with mouse buttons, and are possible only when the Navigation tool is selected on the viewer control bar. Rotation changes the compass direction and the vertical angle from which you see your data. By changing the compass direction, you control whether your perspective is from the south, north, and so on. By changing the vertical angle, you control how high above the horizon your perspective is. Zooming is a navigation operation that controls the extent of the visible area of a 3D scene. From the position of the observer, zooming-in enlarges the object by moving the observer closer to the object while zooming-out reduces the apparent size of the object by moving the observer farther away. Panning is a navigation operation that lets you change the target, that is, the point in the data on which your view is centered. By panning, you can examine areas of a data set which, at the present zoom level, lie outside the field of view. You can move the target up, down, or sideways to see different parts of a data set. Using the Viewer Control Bar The viewer control bar lets you perform basic operations in a 3D scene. For example, let's examine the first two buttons.The Identify tool allows you to identify features in TIN, grid, and feature themes. (When you identify a location in a TIN theme, the interpolated elevation, slope, and aspect values are given for the location you click on. Slope is expressed in degrees from 0 to 90, where 0 is flat and 90 is vertical. Aspect, or compass direction of slope, is expressed in degrees from 0 to 360, where 0 is north and the values progress clockwise (90 is east, 180 is south