Obtaining Aerial Images from Google Earth

Transcription

1 Obtaining Aerial Images from Google Earth Introduction This tutorial will demonstrate how to use the Google Earth application to obtain a site-wide aerial photograph for a modeling project. The tutorial will use the test case file included with the BEEST for Windows software to illustrate the process. Install Google Earth If Google Earth is not installed on your computer, you can obtain it from the website Click the Download Google Earth button to obtain the latest version of the program. On the next page, click the Agree and Download button and save the program GoogleEarthSetup.exe to your computer. Run this program to download and install Google Earth. Locate Facility Before downloading an image from Google Earth, the center point and boundaries for the image need to be determined. In this tutorial, the image will be for the area covered by the facility in the test case file. Open BEEST and Google Earth. In BEEST, click File "Load and Run TestCase" to load the test case file. Click the Zoom In button four times to see the building and source defined in the file. The location of the building will be used as the center point of the aerial image. In Google Earth, click Tools Options and set the Show Lat/Long option to Universal Transverse Mercator. You will need to convert the building location from UTM to latitude and longitude to use it in Google Earth. Coordinate conversion can be accomplished using a program such as Corpscon from the U.S. Army Corps of Engineers. The latitude and longitude for the building are shown in Table 1. UTM 358, meters East 3,936, meters North Zone 17 Latitude and Longitude N W Table 1: Building location. 1

2 Figure 1: Building location in Google Earth. In Google Earth, go to the Search text box, enter the coordinate N, W (without quotation marks) into the text box and press the Enter key. Google Earth will then display the location of the facility (see Figure 1). Define Image Boundaries After locating the facility in Google Earth, you will need to determine how much of the area around the center point to include in the image. To set the area in Google Earth, you will need to add the locations of the southwestern and northeastern corners of the image. Go to the menu bar in Google Earth and click View Reset Tilt and Compass. Go to the toolbar and click the Add Placemark button. A window will appear and display the placemark s name, shape, and coordinate. Delete the name and drag the popup window to the left side of the screen. You will see the placemark in the center of the screen. Click the placemark and drag it to a location southwest of the building. Click the yellow pin button in the popup window to select a different shape for the placemark. Select the Cross Hairs and set its color to yellow. Click OK twice to save the placemark. 2 shape

3 Figure 2: Image boundaries. Add another placemark, delete its name and drag it to a location northeast of the building. Click OK and then hide the placemark Google Earth generated for the building by clicking the checkbox underneath the Search text box (see Figure 2). Save Image Click File Save "Save Image" in Google Earth. Name the file test.jpg and save it to a folder on your computer. Open an image editor, such as GIMP ( or Windows Paint and open the file test.jpg in the editor. Select the area from the center of one placemark to the center of the other placemark and click Edit Copy to copy the selection to the clipboard. In Windows Paint, click File New to create a new image. If you see a prompt to save the test.jpg file, click the Don t Save button. Click File ProperHes on the ribbon bar. 1 1 In Windows XP and Windows Vista, click Image AJributes on the menu bar. 3

4 Select pixels as the units, enter the value 1 for both the width and the height and click the OK button. Click Edit Paste and save the new image with the name aerial.jpg. In GIMP, click Edit Paste as New Image. A new window will open and display an image containing the selected area. Click File Export and save the new image with the name aerial.jpg. View Image in BEEST Click the Show Background Map button in BEEST. Click the File button to set the image filename. Select the file aerial.jpg and click the Open button. You will now be prompted to enter the southwest and northeast corner coordinates for the image. This prompt only appears the first time you load the image; after that, BEEST sets the coordinates automatically. In Google Earth, move the mouse over the placemarks you previously added. Click the right mouse button on each placemark and then click Properties on the menu that appears. The UTM coordinates for the placemarks will be displayed. Copy the coordinates and paste them into BEEST. Click the Save Locations button and then click the Show MAP button to view the aerial photo in BEEST (see Figure 3 on the next page). The appearance of the aerial photo in BEEST can be changed by clicking the up and down arrow buttons next to the words Background Map Gamma on the left side of the screen. Clicking the down arrow button makes the aerial photo darker. Clicking the up arrow button makes the aerial photo lighter. The buttons can be clicked multiple times. The file aerial.jpg is not changed when the buttons are clicked; only its appearance in BEEST is changed. Limitations Site-wide aerial photographs correspond closely to the actual facility locations on the surface of the Earth. However, there are three sources of error associated with obtaining aerial photographs from Google Earth: Make sure that the top of the screen points north and that you are looking straight down at the Earth before you save the image in Google Earth. Select the area between placemarks carefully in the image editor. The farther you zoom out from the center of the facility, the less closely Google Earth s coordinates correspond to the actual coordinates on the surface of the Earth. 4

5 Figure 3: Aerial image has been imported into BEEST. 5