ArcMap and Google Earth

Transcription

1 ArcMap and Google Earth Prepared by Andrew Hobby CVEN 658 November 25, 2008 Contents: Brief Overview of Google Earth Goals of Exercise Computer and Data Requirements Procedure: 1. Creating a KML File 2. Opening KML Data in Google Earth 3. Capturing Images from Google Earth 4. Georeferencing Google Earth Images in ArcMap Brief Overview of Google Earth Google Earth is virtual globe computer program, first released to the public in The globe consists of satellite and aerial photographs of most of the earth, and allows for users to zoom in and out for more or less detailed views. ArcGIS and Google Earth allow for some inter-compatibality through the use of Keyhole Markup Language (KML). KML, a programming language similar to HTML, was specifically designed to allow spatial map data to be displayed in virtual earth browsers, such as Google Earth. By supporting KML, ArcGIS allows shapefiles to be converted for viewing in Google Earth. Views from Google Earth can be saved as a JPEG file, but Google Earth doesn t provide an automatic method of including geospatial reference data with the image. Therefore, this information must be added to the image manually by a method known as Georeferencing.

2 Goals of the Exercise Introduction to: Converting Shapefiles into KML Using Google Earth Importing KML files into Google Earth Copying Google Earth Aerial Images into JPEG Importing and Georeferencing JPEG Images Computer Data Requirements To carry out this exercise, you will need a computer that runs ArcGIS 9.3. Also, you will need Google Earth loaded onto your computer. You will be working with the following spatial datasets during this exercise: Main Folder: KMLTutorial BrazosCounty.shp containing the outline of Brazos County BrazosRds.shp containing the roads of Brazos County CSCityLimits.shp containing the College Station city limits

3 Procedure 1). Creating a KML file In this section of the exercise you are going to create a KML file of the roads within the College Station city limits. (1) Open ArcMap from the Windows Start menu (2) Add BrazosCounty.shp, BrazosRds.shp, and CSCityLimits.shp to the data frame using the Add Data tool. Save the map with the name of your choice. Make sure the projection of the data frame is GCS_North_American_1983. To do this, right click on layers, and click properties. In the screen that opens click the tab labeled Coordinate System. The GCS_North_American_1983 coordinate system is located under Predefined>Geographic Coordinate Systems>North America>North American Datum (3) Using the clip command located under ArcToolbox (Analysis Tools>>Extract>>Clip), use the layer BrazosRds for the input feature, use CSCityLimits for the clip feature, and save the output feature in your working directory as CSRoads.shp. (4) Now we will convert this new shapefile into a KML file. From ArcToolbox, select Layer to KML (Conversion Tools>>To KML>>Layer to KML). (5) Take look at the wizard that opens. The box labeled layer allows you to select which layer you will export. The output file box lets you give a name and directory for the output file. The output file will be in the.kmz format, which is a zipped version of KML. The layer output scale lets you change the scale of the KML file. The three properties dropdown menus are options which allow you to adjust the extent and resolution of the KML. (6) In the wizard, select CSRoads.shp under layer. Name your output file CSRoads.kmz by clicking on the folder to the right of the Output File box. For Layer Output Scale, type 1. Click OK.

4 (7) You have now created a KML file named CSRoads.kmz containing the roads of College Station. 2). Opening KML data in Google Earth In this section, you are going to open and explore the KML file you just created in Google Earth. (1) Open Google Earth from the Windows Start menu (Start>>Programs>>Tools>>3DEarthPrograms>>Google Earth>>Google Earth) (2) Now open the KML file from your directory. Go to File>>Open and browse to your directory. Open CSRoads.kmz. When you open the KML file, Google Earth will automatically zoom in to its location.

5 (3) You can zoom in and zoom out by using the buttons at the top right of the screen. (4) In the Layers menu on the left hand side of the screen, you can unselect Geographic Web and Borders and Labels to clean up the image. (5) Now zoom in and see how well the roads from the shapefile match the roads in the aerial photos.

6 3). Capturing Images from Google Earth In this section, we will save an image from Google Earth as a JPEG file and import it into ArcMap. (1) In Google Earth, zoom in so that you can clearly see the main part of the Texas A&M campus. (2) Under the Places menu on the left hand side of the screen, uncheck CSRoads. It is necessary to uncheck the KML file, so it doesn t appear in the image.

7 (3) To save the image, go to File>>Save>>Save Image. Navigate to your directory and save the image as TAMUcampus.jpg. You have now saved the aerial photo of the Texas A&M campus as a JPEG image. (4) Now open the JPEG image in ArcMap. Use the Add Data tool to add TAMUcampus.jpg from your working directory. When you click OK, a warning message will appear stating that the image is missing spatial reference data. Click OK. Since it is missing spatial reference, the next step will be to provide spatial reference data for the image. 4). Georeferencing Google Earth images in ArcMap. (1). Go back to Google Earth. Under the places menu, recheck the box next to CSRoads. The KML data showing the roads of College Station will re-appear on top of the Google Earth images. (2). Now click on the Tools menu at the top of the window. Navigate to Tools>>Options. In the wizard that appears, in the Show Lat/Long section, change the selection to Decimal Degrees. Then click OK.

8 (3). You will now add 4 placemarks at the intersections of George Bush Blvd. and Texas Ave., University Dr. and Texas Ave., University Dr. and Wellborn Rd., and Wellborn Rd. and George Bush Blvd. These intersections bound the main campus.

9 To add placemarks, click on the Add Placemark button on the menu above the main screen. The button looks like a yellow thumb tack. It will later be necessary for you to remember exactly where you placed your placemarks, so always add them to easily recognizable locations. (4). Now that the Placemarks are added, open notepad. Start>>Programs>>Accessories>>Notepad Save the document that opens in your working directory as CornerPoints.txt. Now type name, ycoordinate, and xcoordinate for the headers. Be sure to separate the headers with Tab. Next, copy the data for each of the four Placemarks you added in Google Earth.

10 To see the longitude and latitude of a Placemark, right click on it and click properties.

11 (5) Once all the Placemarks latitudes and longitudes have been entered, save the file and navigate back to ArcMap. Add the Georeferencing toolbar. To do this, go to Tools>>Customize and check the box next to Georeferencing. (6) Now, go to Add Data, and add the data for the four corner points, CornerPoints.txt. (7) Go to Tools>>Add X Y Data. In the wizard, select CornerPoints.txt, and make sure the X Field and y Field contain the correct columns. Click OK.

12 (8) A warning message will appear saying the points lack an object-id field. This is okay, since we will only be using them to locate the aerial photo. (9) Now zoom in to the area bounded by the four points.

13 (10) Zoom in so the four points fill most of the screen. Then Under the Georeferencing menu of the Georeferencing toolbar, select Fit to Display. The aerial photo should now show up in nearly the right place. To finally adjust the image, use the Add Control Points button in the georeferencing toolbar. First click on the JPEG image where your point should be, then click on the corresponding point. When you have added control points for all four intersections, the image should automatically have zoomed and rotated and should now match the roads in the CSRoads layer. (11) When you have added control points for all four intersections, the image should automatically have zoomed and rotated and should now match the roads in the CSRoads layer. Now under the Georeferencing dropdown screen in the georeferencing toolbar, select update georeferencing, to permanently create spatial references for the JPEG file. (12) If you right click on the JPEG and go to properties, you will see that geospatial data for the image is now included under the source menu.

14 (13) Your final display in ArcMap should look something like this.