LAB #7 Creating TIN and 3D scenes (ArcScene) GISC, UNIVERSITY OF CALIFORNIA BERKELEY

Transcription

1 LAB #7 Creating TIN and 3D scenes (ArcScene) GISC, UNIVERSITY OF CALIFORNIA BERKELEY The purpose of this laboratory is to introduce and explore surface data analysis using a vector data model: TIN. We will load the 3D Analyst Analyst Extension, create an elevation model of a study area from point, line, and combined point/line data, and active a new 3D software tool: ArcScene. A Practice Data Set: The Claremont Canyon Region DataSet

2 7.1 Introduction: Three Dimensional Data 7.2 Getting Started: The ArcScene Interface 7.3 Creating a TIN 7.4 Thematic Display of TINs 7.5 Draping Layers on Your TIN 7.6 TIN to Polygon Conversion 7.7 Assignment Note: Some of the graphics in this module are from ESRI s ArcGIS Resource Center

3 7.1 Introduction: Three Dimensional Data (back ground information) ArcGIS uses an extension called 3D Analyst to visualize and analyze 3D surface data. It allows you to: - create digital models of geographic surfaces, (such as the image shown above) - display the models in three- dimensions using the application ArcScene - analyze various properties of these models In previous labs, we used ArcMap for displaying and analyzing 2 dimensional data. In this module, we will primarily use ArcScene, which is the ArcGIS application that allows you to view, create, and analyze surfaces in 3D. (You can also use ArcMap to perform many of these same functions, but you can only view the surface in 2 dimensions in ArcMap). When using 3D Analyst, you will most commonly work with both surface raster and vector data to create 3D models. Three Dimensional Data There are 3 main data types that 3D Analyst supports: 1. Raster 2. TINs (Triangulated Irregular Networks) 3. Shapefiles You are familiar with Rasters and Shapefiles from the previous labs. If you recall, Rasters are pixel images, such as orthophotos, and shapefiles are vector representations of geographic data. In 3D Analyst, the data contains a z- dimension, in addition to the x, and y coordinates of a geographic point. Three Dimensional data GRIDS (type of Raster data) Continuous spatial data is often stored in grid format. A grid defines geographic space as a matrix of identically- sized square cells. Each cell holds a numeric value that measures a geographic attribute (like elevation) for that unit of space. Discrete grids: categorical information such as land use categories or ZIP codes. Continuous grids: describes data along a range of values, such as ph or elevation data.

4 Creating grids: 1. Convert to a grid from a feature theme; either a CAD file or a shapefile. Polygons, lines and points can be converted. Image layers with single or multiple bands can be converted to a grid. 2. Create a grid using either of four interpolation methods: Inverse Distance Weighted Spline Kriging Polynomial Trend fit 3. Create a grid from a TIN through the use of linear interpolation. Three Dimensional data TINs (Triangulated Irregular Network):

5 For the purpose of this laboratory and in most of your classes, you will work with TINs: TINs (or Triangulated Irregular Networks) are representations of 3D surfaces that use a set of contiguous, non- overlapping triangles to describe a geographic surface. TINs can be created from a number of data sources, including points, lines, and polygons. For example: - Digitized contour lines (hypsography), - Spot elevations from GPS or survey data, - Satellite LiDAR data or NED data, - Underwater spot elevations from sonar surveys (bathymetry), - Borehole data, etc.

6 Three Dimensional data Shapefiles Shapefiles contain vector data stored as x, y, and z coordinates to define simple, discrete geometry such as points, lines, and polygons. Two dimensions can be converted to three dimensions by either using attributes or by overlay. Attributes for thematic data can be used for heights to create a three- dimensional block diagram. Data can also be overlaid on any surface and thereby acquire Z values. CAD files that have a Z component can be directly loaded into a 3D view and viewed in three dimensions.

7 Visualizing Data in Three Dimensions Three- dimensional data can be viewed from any angle by rotating and tilting the object but also zooming in and out, panning and moving back and forward. The user also has control of the light source and can thus alter shading. Two- dimensional data can be temporarily converted to three dimensions and can be viewed in perspective without the need to create three- dimensional datasets. Many other features help to make the 3D analyst a versatile tool for 3D visualization. More on this in the following exercise. Analyzing Data in Three Dimensions Surface Analysis Surfaces are used in a wide variety of spatial analysis, such as suitability studies, hydrologic analysis, line- of- sight, slope, and aspect analysis. Surface analysis is an important to increase the understanding of continuous data. 3D Analyst allows you to perform a wide range of analyses on the surfaces that you create. For example, you can perform: Viewshed Analysis - Determine what is and is not visible from a certain point in the landscape.

8 Height Profile - You can determine the height profile along the bank of a creek, or a canyon Slope/Aspect Analysis - You can determine the percentage slope and aspect of a given part of the landscape

9 Slope Aspect 7.2 Getting Started: The ArcScene Interface Navigating the ArcScene interface is very similar to ArcMap.

10 However, because of the third dimension, ArcScene uses its own Toolbar:

11 The default tool is. Left clicking allows you to rotate and move the view around in 3 dimensions. Clicking the mouse- wheel allows you to Pan Right clicking activates a Zoom feature. You can also zoom using the mouse- wheel. There are a few other cool tools like Fly: And Observer : Fly allows you to start a basic flight simulator with which you can "fly" through the digital model. Observer allows you to place the view as if you were a person standing at a specific point on the surface. Similar to ArcMap, you add data using the button. Display order, (as in ArcMap) is controlled by moving layers up and down in the control panel.

12 7.3 Creating a TIN Launch the 3D Analyst extension. Make sure the 3D Analyst extension is checked. Launch the 3D Analyst Toolbar. For this exercise, we will use a base set of contour data that was generated from a NED (National Elevation Database) that I downloaded from the USGS Seamless Server. I downloaded three NED data sets: 1 Arc Second, 1/3 rd Arc Second, and 1/9 th Arc Second. NED data are created by using lasers (shot from the Space Shuttle) that measure the ground elevation. LiDAR produces a similar data base and is becoming very popular in Landscape Design and Planning. This NED data is available for almost any area of the country, and thus knowing this process will allow you to create a digital terrain model for any location in the U.S. I used the Spatial Analyst Tools: Surface Contour and generated four sets of contours for the sample region. NED1arc (is the 1 Arc Second data base) that I used to generate contours with a 30 meter contour interval (cont_30m). NED1_3arc (is the 1/3 rd Arc Second data base) that I used to generate contours with a 15 meter contour interval (cont_15m). NED1_9arc (is the 1/9 th Arc Second data base) that I used to generate contours with a 5 meter contour interval (cont_5m). NED1_9arc (is the 1/9 th Arc Second data base) that I used to generate contours with a 1 meter contour interval (cont_1m).

13 Note: From the contours we can create a TIN of the sample area. It is important to use a set of elevation points or contours that form a convex shape or can effectively be bounded by a convex boundary when building a TIN. Concavity produces boundary error. Load the 5 meter contours (cont_5m) that were created from the NED data: Creating a TIN from Contours We will use the 3D Analyst extension to create a TIN from the contours we just loaded: We can use either ArcMap or ArcScene to do this (ArcMap has a little more power but the results in ArcScene are immediately more interesting). Launch ArcScene and add the Contours layer.

14 Note that the contours are lying flat. This is because we have not defined their base heights and there is no current Z value in the shapefile. We will see later that we can permanently assign a Z value to a contour line. We can define the contour base heights before creating a TIN from the contours. Right click on the layer and choose Properties - - then click on the Base Heights Tab. Use the expression builder to select the Spot_ft attribute field. Click, and you'll see the contours are now displayed in 3D. Since we already launched the 3D Analyst extension, the 3D Analyst toolbar should be available: If not, go to Customize Toolbars 3D Analyst and launch it.

15 The toolbar is slightly different in ArcMap and ArcScene. in ArcScene in ArcMap Make sure you have ArcToolbox launched. We can Build a TIN in either ArcMap or ArcScene. I will use ArcScene in this example. Click the Create TIN Since our contours and the data frame are in the California State Plane Zone III, NAD 83 and feet, make sure you are using the height_field the Spot_ft field

16 to generate the TIN as we want x,y and z to all be in feet. Surface feature type (SF_type) The surface feature type helps define the TIN surface and categorizes the input features according to behaviors associated with their vector type. Points, for instance, can only be added as mass points. However, line features can be represented as hard or soft breaklines, and polygons can be hardclip, softclip, hardreplace, softreplace, harderase, softerase, hardvaluefill, or softvaluefill. Hard and soft qualifiers for line and polygon feature types are used to indicate whether a distinct break in slope occurs on the surface at their location. A hard line is a distinct break in slope, while a soft line will be represented on the surface as a more gradual change in slope. Choose the Softline option here as the contour lines are representations of gradual slopes without a sudden break mapped by a give isopleths or contour line.

17 After a few minutes (depending on the speed and memory of your computer), the TIN should display in ArcScene, and you have your first digital terrain model. If this crashes your computer, it is likely due to the TIN being too detailed and your computer resources are limited. We can make another TIN from 15Meter contours (cont_15m), instead of the 5Meter (cont_5m) contours. Turn off the tin5m from ArcScene and build another TIN made from 15Meter contours and call it: tin15m. Notice that the TIN built from cont_15m is still quite detailed when zoomed out. In some cases, you may want to have vertical exaggeration in your terrain models (commonly done when representing very large areas as viewing them on a small flat screen can produce visual illusions). To do this, right click on the TIN and choose Properties Base Heights Elevation from features

18 Identify Floating on a custom surface and convert the layer elevation to scene units where custom = 2.0 or twice the current Z value. You can also use this tool to convert from meters to feet or vice versa, rather than calculating another field in the Attributes Table.

19 Now our sample area starts looking more like the Himalayas than the East Bay Hills: 7.4 Thematic Display of TINs ArcScene allows you to change the symbology of your TINs to reflect percentage slope, slope aspect, elevation etc. The process is very similar to changing the symbology of a layer in ArcMap. Right click on the tin layer and choose Properties.

20 Then click on the Symbology tab:

21 In the top left corner, you have the option to choose what to display: Click the Add button: different display modes. And you'll have the option to select from a number of Choose the one you want and click 'Add'. When finished, click 'Dismiss'

22 With Elevation loaded and checked, uncheck the Edge Types and Faces and click to exit out of the Properties menu and see the result: Edit the properties and set custom to 1.0 so your surface no longer resembles the Himalayas Now, experiment with different themes. Try displaying the TIN with slope percentage, and with slope aspect. You might have to rearrange the color ramps to get a good display:

23 Here is the same TIN displayed as slope percentage: Notice the random intervals shown on the left. This is caused by Classifying with Natural Breaks in the symbology Tab:

24 To change this to something more meaningful, such as 10% increments, click the classify button: Now click the Method Drop down menu and change the settings to: Defined Interval, and the Interval Size to 10:

25

26 Click, and see the changes: You can also choose to display multiple themes on one map. For example, you can display both the shaded TIN and the contours from which it was generated. To do this, simply check both boxes under the Symbology Tab: Click, and you'll see the contour lines sitting on top of the TIN.

27 7.5 Draping Layers on Your TIN ArcScene allows you to drape other layers on top of your TIN. For example, you can drape the streets layer to give the streets a Z value. Or you can drape an orthophoto of the area. Add the cc_streets layer to ArcScene: Right click cc_streets and Choose Properties. Then click on the Base Height Tab: Select your tin as the Base Height The roads are displayed in 3D:

28 You can also display buildings in 3D by providing a Base Height and extruding them a given distance above the base height. Add cc_houses to your ArcScene. This is also done in the Base Heights Tab under Layer Properties: Click on the Extrusion tab:

29 Extrude the buildings 40 feet in 3D

30 One can also change the way ArcScene handles shadows, lighting, and even the background color. Right click on Scene Layers and Click on Scene Properties: For example, Click the Illumination Tab to deal with shading issues. For more information about creating Thematic Maps and to perform Viewshed Analyses, you can read Using 3D Analyst:

31 7.6 TIN to Polygon Conversion When you create a product from surface modeling in TIN you can convert it to use in other analysis such as Suitability Analysis. The following is an example of how to convert the interpretation of a classified Slope map into a set of polygons to be used in a Suitability model. Once you have a satisfactory slope model from your TIN analysis, use the Conversion tools in ArcToolbox, TIN Triangle.

32 I used a relatively accurate data model so I have thousands of triangle polygons. Change the display properties. Graduated colors and use Slope_degree as the Field value. Load the result to ArcMap if it is not already loaded.

33 A warning occurs as I have many triangles, just click OK to continue.

34 Don t forget to turn the Outline Color to no Color or you will again have a map displaying so many edges of each small triangle that the map will be all blackened lines. Slope is now calculated in triangle polygons.

35 Selects only the steepest slopes where ill sides will likely fail. export the selected polygons Data Export Data

36 The steepest polygons. Dissolve these into larger polygons. Use the data table Field OID if all the values are 0. If not, Add a new Data Field and calculate all the values equal to the same value. With all the records = 0 (like I have in this example), dissolve based on that field.

37 The dissolved polygons ready to incorporate in an overlay analysis like a suitability analysis.

38 7.7 Assignment: A TIN Model to facilitate Housing Suitability Using the Claremont Canyon Data Set provided in this laboratory... Q1: Create a new set of Contours from one of the NED files in the lab7_132.gdb Geo-database using tools in "Spatial Analyst Tools" or 3D Analyst Tools. DO NOT use the contour intervals of those contour features delivered with the Geo-database In other words, do not use contour intervals 1, 5, 15 or 30. (2 marks)

39 Q2: Create a TIN from the Contours you create in Q1 and display the faces in a single color symbol. Drape the Claremont.jpg Digital Ortho Image over the TIN and display it in 3D. (2 marks) Download Claremont image here (It has no projection datum defined it is California State Plane ZoneIII, NAD83, Feet) Q3: Drape 1 line layer and 1 polygon layer on your TIN surface. Place the houses on your surface and extrude them 60 feet. What do you notice about the draped polygon layers? (2 marks) Feel free to display these layers separately as they will not drape and easily display on top of each other.

40 Q4: Generate a new Aspect map from your TIN, convert it to a polygon feature class, dissolve the polygons into N, NW, NE,W, E, SW, SE, and S. Drape the new Aspect polygons on your TIN and display it in 3D. (3 marks) Q5: Post your results as a.pdf file to bspace. Include in your document the simple geo-processing necessary to each of the graphics you submit.. (1 mark for overall clarity and communication) Some Hints on processing some of the data for this lab assignment: 1. How to make a contour from a raster?

41 2. How do you create an aspect map from a TIN? Using a TIN Display Aspect symbology

42 Then use the Surface Aspect tool.

43 Look at the Attribute Table. We need to add N, NW, NE,W, E, SW, SE, and S to the table. You can make your own in an excel spreadsheet or use the following comma delimited table I used here My table. Join the AspectCode.csv table to your new shapefile.

44 3. How to convert 2D features to 3D features by deriving the height value from a surface. Converting 2D features to 3D features using a TIN You can convert 2D features to 3D features by deriving the height value from a surface. The ArcToolbox Functional Surface Interpolate Shape tool allows you to obtain 3D properties from a surface. ArcToolbox Functional Surface Interpolate Shape Opens the following wizard:

45 Here I use my 2D streets and convert them to 3D using my TIN surface that I built from the USGS NED data I got on line at the Seamless Server; this data derived from the Space Shuttle mission. Click The processing concludes with a positive response The new data files now has x,y and z values embedded.