• General Introduction
• Creating TINs from Vector Data (Exercise I)
  • Introduction and Background
  • Data
  • TIN Creation Procedure
  • Displaying & Comparing TINs
  • Printing TINs
• Extrusion Visualization of Geospatial Data (Exercise II)
  • Introduction and Background
  • Data
  • Procedure
• To Turn In
   

1.0 General Introduction

As computer graphics capabilities have continued to advance, 3-D visualization of geospatial data has become an increasingly prominent part of GIS. In this lab you will work with two types of 3-D visualization: terrain visualization (in the form of TINs) and extrusion display. You willl also try out one of ESRI's global visualization modules, ArcGlobe.

Exercise I

2.0 Creating TINs from Vector Data

2.1 Introduction and Background

A Triangulated Irregular Network (TIN) is a surface representation composed of a network of triangles derived from irregularly spaced point data. TINs can be created from any point data having a Z value, but are most commonly used to represent terrain. Each triangle in the TIN is essentially a facet with a specific slope and aspect. The Z values enable these facets to be visualized as a three-dimensional surface, making for a striking and efficient representation of a landscape.  (In actuality, the surface will be 2.5D because every location will only be represented with one elevation.)

The basic TIN creation process: Triangulation of irregular points (Source: ESRI)

In this exercise you will be creating TINs from both point and isoline data. The dataset covers the La Conchita, California area and was digitized from data originally collected by the USGS in 1947. It was created as part of an investigation into the cause of the 1995 landslide there. Tragically, an even larger landslide occurred in the same location in January 2005 due to heavy rains, resulting in several fatalities.

For additional information on TINs, consult your textbooks (Longley 189-190) and ArcGIS Help.

Question 1:  Define mass points and breaklines. What is the difference between soft and hard breaklines? Question 2: What else might a TIN be useful for? (besides anything to do with elevation) Describe a specific data source you could visualize as a TIN surface. hint: you might want to consult ArcGIS Help, the course textbooks, and the Web.

2.2 Data

Download lab6_data.zip and extract the files to a Lab6 folder on your removable disk.

The datasets we will be using in this current exercise are in the laconchita_1947 folder. These are two shapefiles: a points layer (q1947pnts) and a contour line layer (q1947cons). Fortunately, ArcGIS can make TINs directly from shapefiles, coverages and feature classes, so we will not need to do any file conversion.

2.3 TIN Creation Procedure

This exercise will use the 3-D Analyst Tools. 3-D Analyst offers tools for creating 3-D visualizations and the ability to create and manage TINs. It will also give you some exposure to the related ArcScene module.

Begin by opening ArcMap and loading ArcToolbox within it. Add the q1947pnts and q1947cons datasets to the display. Notice that these datasets are not projected, yet when you add them to ArcMap, you should recognize the coordinate system.  These datasets show elevation sample points and contour lines for La Conchita. 

Step 1: Create empty TINs

The first step is to create empty TIN files to serve as templates for the three actual TINs we will be creating.

Find the Create TIN tool (in ArcToolbox) under 3-D Analyst Tools -> TIN Creation and double-click on it. Set the Output TIN as tin_47_pts in your Lab6 folder. Next, to set the projection, click on the button next to the Spatial Reference text input box. This opens the Spatial Reference Properties window. Click on the Select button and navigate through the files to Projected Coordinate Systems -> State Plane. Choose NAD 1927, California Zone 5 as the projection. Click OK, then click OK again to close the Spatial Reference Properties window.

Finally, click OK on the Create TIN window to make the file.

The new tin_47_pts file will created in your Lab6 folder with no features in it.

Now repeat this procedure to create two more empty TINs named tin_47_con and tin_47_both. Save them in Lab6 and give them the same projection as above.

Step 2: Derive TIN from point data

Now that we have template files, we can start deriving TIN surfaces from the La Conchita datasets. The first TIN will be based on the q1947pnts point shapefile.

Find the Edit TIN tool under 3-D Analyst Tools -> TIN Creation and double-click on it. Set the Input TIN as tin_47_pts (your first template file). The next item in the window, Input Feature Class, is used to add the dataset(s) from which the TIN will be derived. Add q1947pnts by using the browse button  or the drop down arrow next to the text input box. The dataset will now appear in the listing. You can set the various parameters in the listing by clicking on each cell and making a selection from the drop-down menu. Change height_field to "SPOT" (i.e. the spot heights attribute) and make sure SF_type is set to "masspoints".

Finally, click OK on the Edit TIN window.

The TIN will now be created.  Click the Add Data button and navigate to the tin_47_pts tin and add it to your map.  You can turn the points and lines off to see it.

Step 3: Derive TIN from contour data

The second TIN will be derived from contour line data, found in the q1947cons polyline shapefile. Although this is line data, ArcGIS is still in fact using point data for the triangulation -- the vertices of the contour lines are the inputs.

Find the Edit TIN tool under 3-D Analyst Tools -> TIN Creation and double-click on it. Set the Input TIN as tin_47_con (your second template file) by browsing to your Lab6 folder to find it. Under Input Feature Class, add q1947cons to the listing. Change height_field to "SPOT" and make sure SF_type is set to "masspoints".

Finally, click OK on the Edit TIN window.

When the process is complete, use the Add Data button to add the tin_47_con tin to your map. 

Step 4: Derive TIN from both datasets

The third TIN will be derived from both points and contour line data.

Find the Edit TIN tool under 3-D Analyst Tools -> TIN Creation and double-click on it. Set the Input TIN as tin_47_both by browsing to it in you Lab6 folder. Under Input Feature Class, add q1947pnts to the listing. Change height_field to "SPOT" and make sure SF_type is set to "masspoints". Next, add q1947cons to the listing. Change its height_field to "SPOT" and change SF_type to "softline".

Finally, click OK on the Edit TIN window.

When the process is complete, add the tin to your map.


2.4 Displaying & Comparing TINs
 
Now that all of the TINs have been created, we will examine the differences among them.

First, compare the three TINs to one another visually by turning them on and off in the display (via their Table of Contents checkboxes). Be sure to not have more than one TIN layer active in the display at a time.

To make the comparisons easier, we should set the symbology of the TINs to something a little more revealing. Start with the tin_47_pts TIN. Right-click on the name of the layer in the Table of Contents and choose Properties, then click on the Symbology tab. The Show column on the left-hand side of the window lists the various feature types being symbolized. In this case, the only feature listed will be Elevation. Uncheck this item.

Click on the Add button along the bottom of the Show column. This brings up the Add Renderer window.

Highlight "Face elevation with graduated color ramp" and click Add, then Dismiss to close the window. The Symbology window should now update to show several elevation classes and their associated colors. Above these, click on the Symbol column heading and choose Flip Symbols.

The color ramp should reverse so that white is at the top and blue is at the bottom (which will yield a more intuitive color scheme). Finally, click OK to apply the display changes and close the Properties window.

Now apply the same process to tin_47_con and tin_47_both to give them an identical symbology. For tin_47_both you will notice a different Show column listing. Because a contour line dataset went into creating it, by default the contour lines will also display, listed in the Show column as an "Edge types" feature type. Whether or not you want to have the contour lines displayed is up to you; however, examining them will help you understand how they are used in creating the TIN.  If you want them to display, be sure to move them to the top of the Show list by using the up arrow next to the Add button.

There are additional display options available via the Add Renderer window that you can use to further explore the nature of the TINs. To display the actual points used to construct the triangles, you can add one of the "Nodes" options (with "Nodes with the same symbol" being the most appropriate here). To display the outlines of the triangles, add "Edge type grouped with unique symbol" to the listing. Experiment with using these options.

Using ArcScene

You can also change the display perspectives of the TINs by opening the TINs in ArcScene rather than ArcMap.

Begin by opening ArcScene (Start -> Programs -> ArcGIS -> ArcScene) and add the 3 TINs as data layers. Notice that only the Faces are rendered. That is, the TINs are now uniformly green without displaying the classified elevations.
The Navigate tool will rotate the image in the direction of cursor movement -- left-click and drag the Navigate cursor in the desired direction to move it. A fun alternative for changing the perspective is the Fly tool . This enables you to "fly" across the landscape of the TIN at various speeds. Left-click to begin moving, and direct your flight path with the cursor. Left-click additional times to increase speed, and right-click to reduce it (your speed setting will be displayed in the lower left of the main window). Right-click to a negative speed to go in reverse, and hold at a speed of 0 to stop the flight.  You can also use the escape key to stop.

Question 3 Describe the differences in appearance among the three TINs. Think in terms of surface roughness, boundaries of elevation classes, triangle tiling patterns, etc.

For a more objective basis of comparison, you can also examine the basic geometric and statistical characteristics of the TINs. In ArcMap, you can find these by right-clicking on a TIN in the Table of Contents, choosing Properties, and clicking on the Source tab. In the Data Source display panel you will see entries for the number of nodes, number of triangles, and range of Z values for the given TIN. These figures give insight into how the various data sources yield different TIN frameworks.

Question 4 List the number of nodes, number of triangles, and range of Z values for each of your three TINs. How do the input data types seem to affect the resulting TIN frameworks?

2.5 Printing or exporting TINs

There are two ways you can print or export your TINs to graphics. The most straightforward way is to load a TIN in ArcMap as a map layer, and print or export it out as you would a normal ArcGIS map. The disadvantage with this approach is that you are able to only display the TIN from a single, predetermined top-down perspective rather than the multiple possibilities offered by ArcScene.

A more flexible alternative is to insert an image of the TIN from ArcScene into the ArcMap display. To do this, set up the ArcScene display to your chosen arrangement, then click on Edit -> Copy Scene to Clipboard. Switch back to ArcMap and set its display to Layout View, then Paste the scene on the map. Remember, however, that this is a graphic image, not a true map layer, so ArcMap will not be able to derive any spatial information from it -- keep that in mind for your map elements!

Map 1 for Lab 6: Make a map of your favorite 1947 La Conchita TIN. You may use either ArcMap or ArcScene, and display it with whatever features you think are most appropriate.  Export the map to a graphic (jpg, pdf, bmp...) On the map put information about the data source(s): 1) the projection; location, zone, units etc. 2) metadata about the source data; numbers of features (lines-points) in the input coverages, the scale/date of the original source data etc. 3) a description of the TIN (number of triangles and nodes) and the Min/Max Z-values.

Exercise II

3.0 Extrusion Visualization of Geospatial Data

3.1 Introduction and Background

3-D visualization is useful for much more than representing real-world features that have height. A third dimension provides a means of visualizing multiple facets of a dataset simultaneously. An example of this is the technique known as extrusion. Extrusion involves creating a 3-D data display by "pulling" or "raising" a two-dimensional polygon up along a Z-value height to make columns. The resulting image resembles a cityscape of high-rise buildings. In terms of maps, this can be used either to 1) give extra emphasis to features on a map, but not display additional data; or 2) display two dataset attributes at the same time, one represented by the color scheme of the polygons and another by the extruded columns.

In this exercise we will be using extrusion to compare socioeconomic data from the U.S. Census with national voting patterns. This could be done using ArcScene, but we will instead be using ArcGlobe to give you some practice with an additional (and fun!) ArcGIS module.

3.2 Data

The dataset we will use in this exercise, the 2004election_county shapefile, can be found in your Lab6 folder that you created previously. The shapefile contains voting data at the county level for the 2004 U.S. Presidential election, covering the lower 48 states.

3.3 Procedure

This exercise will use ArcMap as well as ArcGlobe, one of ESRI's modules for global data display. (The other is ArcExplorer)  We will first symbolize the dataset in ArcMap, then import it in ArcGlobe to do a 3-D extrusion visualization.


Step 1: Examine & symbolize data

Start a new map in ArcMap and add the 2004election_county shapefile to the display. You will see a map of U.S. counties.

Take a moment to look through the 2004election_county attribute table. You will see that the attributes are a combination of Census data followed by various categories of election results. The election data include total vote counts and vote percentages for George Bush (B) and John Kerry (K) in each county. The very last field, "Winner", lists which candidate won the majority of votes in each county. This is the attribute we want to display on the map.

Right-click on 2004election_county in the Table of Contents and choose Properties, then click on the Symbology tab. In the left-hand column, choose Categories -> Unique values as the display type. Change the drop-down Value menu to "Winner" and click on the Add All Values button. Uncheck the "all other values" category at the top of the listing. Change the remaining three classes (Undetermined, Bush, Kerry) to an appropriate color scheme. The standard color scheme for maps of this election has been red for Bush and blue for Kerry, but unfortunately a blue extrusion will be difficult to distinguish from the blue of ArcGlobe's oceans. For your map, try some other useful, non-clashing color scheme (red and yellow would be a reasonable choice). Use a neutral color (such as light gray) for the three Undetermined (blank) counties, and under Label on the Symbology tab type Undetermined for your undetermined class.

When you have settled on a color scheme for the map, you will save it as a layer file (not a shapefile). To do this, right-click on 2004election_county in the Table of Contents and choose Save As Layer File, and save it in your Lab6 folder.


Step 2: Explore ArcGlobe

Start ArcGlobe by going to Start>All Programs>ArcGIS>ArcGlobe.  Take a few minutes to explore ArcGlobe before we begin working with the data. ArcGlobe uses many of the same controls as ArcScene, so you should be able to quickly figure out how to move around in the display.

Once ArcGlobe has loaded, you should see a Table of Contents on the left side of your screen.  If you do not, click on Table of Contents under the Windows menu to show a listing of the data displayed.

After trying out ArcGlobe a bit, add the layer (2004election_county.lyr) you created in the previous step via the Add Data button. When the Add Data Wizard: 2004election_county window appears, click Finish to accept the default rendering properties, and click Close when the Geographic Coordinate Systems Warning appears.  Use the Center on Target tool from the toolbar to center the display on the middle of the US, and zoom in if appropriate.


Step 3: Extrusion

We will now do an extrusion of a second attribute in the dataset. Right-click on 2004election_county in the Table of Contents and choose Properties, then click on the Globe Extrusion tab. Check the box labeled "Extrude features in layer". The panel below it labeled "Extrude value or expression:" determines which attribute (and any modifiers of it you wish to add) will be used for the extrusion. Note that the extrusion units will be meters. Click on the Expression Builder button next to this panel to bring up the Expression Builder window. Scroll through the attributes listed in the Fields panel on the left for "POP00_SQMI" (2000 population density) and click it to add it to the Expression box below. To make sure the extrusion columns will be tall enough to easily view (remember, the extrusion units are meters) add a multiplication by 100 to the expression. Click OK to apply the expression, then OK again. 

It may take a few moments to render the counties.  Be patient.  In order to see all of the counties, uncheck the other layers in the Table of Contents.  Experiment with different formulas to extrude the counties by the year 2000 population density.

You now have a visualization of the population density of each county, colored according to which candidate received the majority of votes in it. Explore the display and look for any revealing patterns.

Step 4: Exploratory analysis

Now that you have learned the extrusion process, it is time to use it for some exploratory analysis on your own. Look through the dataset attributes and try to come up with another socioeconomic factor (i.e. other than population density) that you think you might partially explain the voting pattern depicted on the map. Visualize this factor as you just did for population density above. Be sure to normalize the attribute if appropriate, and give it a scaling factor in the extrusion equation if needed for greater visibility. (Note: Area may not necessarily be the appropriate factor to use for normalizing your attribute!)

Step 5: Export your map

Create and export a map of the 3-D extrusion you created in Step 4 above. ArcGlobe displays are prepared for exporting in the same way as ArcScene and ArcMap displays. Set up the ArcGlobe display to your chosen arrangement, then click File -> Export Globe.

To turn in

• The question sheet, with typed answers (Word document)
• Map of 1947 La Conchita TIN
• 2004 Election extrusion map

Created by Sean Benison

Based on previous lab by Sarah Battersby and Jeff Hemphill
UC Santa Barbara, Department of Geography
© 2000-2007 Regents of the University of California

This page was last modified on March 3, 2008 by Indy Hurt