Working with Elevation Data URPL 969 Applied GIS Workshop: Rethinking New Orleans After Hurricane Katrina Spring 2006

Transcription

1 Working with Elevation Data URPL 969 Applied GIS Workshop: Rethinking New Orleans After Hurricane Katrina Spring 2006 This GIS lab exercise will explore Light Detection And Ranging (LiDAR) data for New Orleans collected as part of a statewide project in Louisiana. The exercise was prepared using ArcGIS 9.0. Step 1. Download and Extract LIDAR Data Use an Internet Browser to access the Louisiana State University Atlas website at Click on the Download Data button and then scroll down and select LIDAR Data. This site can be accessed directly at

2 Begin the selection process for the LIDAR data by using the dropdown menus to complete the phrase -- 1) Select ¼ quad attribute USGS Name starting with New Orleans East. Click Submit. On the left side of the page click on the gray Download button to the right of DEM to download the New Orleans East NE LIDAR Digital Elevation Model (2.70 MB zip file). When prompted with the File Download dialog box, click Save, navigate to an appropriate location and create a folder titled no-lidar in which to save the file. Use the same process to download the DEM for New Orleans East NW (3.18 MB zip file).

3 Use WinZip to extract the compressed files in the.zip files. Step 2. Convert the LIDAR Files into the GRID Format Open ArcCatalog. You can use the icon on the desktop, if available. If not, click on the Start button in the lower left corner of the screen and under programs, choose ArcGIS and then ArcCatalog. Open ArcTools by clicking on the Red Toolbox icon. The LIDAR files are in a USGS DEM format. In the ArcToolbox menu, select Conversion Tools, then To Raster, and finally DEM to Raster.

4 In the DEM to Raster dialog box, make the following choices: Input USGS DEM file: dem_ ne.dem Output raster: no-east-ne Output data type: Integer Click OK and close the window when complete. Repeat the process for the New Orleans East NW file with the following choices Input USGS DEM file: dem_ nw.dem Output raster: no-east-nw Output data type: Integer You now have two LIDAR quarter quads in Arc GRID format.

5 Step 3. Merge the LIDAR Files In the ArcToolbox menu, select Data Management Tools, then Raster, and finally Mosaic to New Raster In the Mosaic to New Raster dialog box, select both the no-east-ne and no-east-nw GRID files as Input Rasters: Choose the no-lidar folder as the Output Location and type no-east-merged as the Raster dataset name with extension.

6 Click OK. When the process is complete, close the dialog box In ArcCatalog, on the Contents window on the left side of the screen, navigate to the nolidar folder and right-click on the no-east-merged GRID file and click on Properties to activate Raster Dataset Properties. View properties for Dataset, Raster, Extent, Spatial Reference, and Statistics.

7

8 Step 4. View Merged LIDAR Data Open ArcMap. Add Data. [no-east-merge] Explore Effects Tools. View >>> Toolbars >>> Effects Transparency, brightness, contrast Right Click on no-east-merge theme in table of contents, select Properties Layer Properties dialog box Display tab (Show Map Tips, Display raster resolution in table of contents)

9 Symbology tab Unique Values (random)

10 Unique values Apply color scheme Click lowest elevation value. Hold shift key and click highest elevation value. On color scheme drop-down, scroll down near bottom and select appropriate color scheme. Click apply. Unique values Separate above sea level and below sea level Click color box for lowest elevation value (-28) shift key and click box for (-1) and then double click to invoke color pallette. Select a light green. Click color box for (1) and then hold shift key for (46) and then double click to invoke color pallette. Select a light red. Click apply. Note extent of area below sea level.

11 Classified Choose 10 classes. Choose appropriate color ramp. Click on Classify button to see histogram and adjust values. Set breaks in groups of five. Click OK. Click Apply.

12 Stretched Click color ramp. Make appropriate selection. Explore stretch type. Explore Histogram button. Step 5. Explore Spatial Analyst Extension Invoke Spatial Analyst Extension Tools >>> Extensions. Make sure Spatial Analyst is available and checked. Also select 3D Analyst.

13 View >>> Toolbars. Make sure Spatial Analyst is selected. Create Contour Tool Zoom in on Fairgrounds Select Create Contour Tool and click on edge of pond in fairgrounds. Zoom to extent. Select Create Contour Tool and click on Mississippi River levee. Experiment with tool. Use Select elements tool in Tools toolbar to select and delete contour graphics.

14 Hillshade Zoom to extent Spatial Analyst drop-down menu >>> Surface Analysis >>> Hillshade Accept defaults in Hillshade dialog box and click OK. Repeat with Z-factor of 0.3. Repeat with Z-factor of 3.2. Experiment.

15 Contours Spatial Analyst drop-down menu >>> Surface Analysis >>> Contours Choose Contour Interval of 2. Click OK. [MAY BE TIME CONSUMING] Use Layer Properties to symbolize contours.

16 Step 6. Explore 3D Analyst Extension View >>> Toolbars. Make sure 3D Analyst is selected. Start ArcScene Add no-east-nw grid Right click theme to invoke Layer Properties Click Base Heights tab Click Obtain heights for layer from surface. Click OK [MAY TAKE AWHILE] Set Z Unit conversion to 15. Use Symbology tab to apply a color ramp. Click OK. In ArcScene, use left mouse click to tilt perspective. Use right mouse click to zoom in and out.

17 Explore Line of Sight tool Explore Create Profile Graph tool Extra Credit: Use MyWebSpace and class group directory to download citywide merged LiDAR data. Extract and explore. To be added later. Explore Hydrologic Modeling Extension. Will need to be installed from Developer s Kit Created by David Hart, University of Wisconsin Sea Grant Institute February 10, 2006