Using Google Earth™ with AutoCAD® Thomas Inzinga – Autodesk GD101-3 After completing this session, you will be able to import image and terrain data into AutoCAD-based products, use that data to help with various design and modeling tasks, and publish DWG-based models to Google Earth for presentation to wider audiences. You will also gain an understanding for the context in which Google Earth data should be used, and for the various options available for publishing DWG data to Google Earth, including temporal data. About the Speaker: Thomas is a software architect for the Autodesk AEC Division. With 24 years of experience, he is an expert in the design, development, and implementation of civil-engineering applications. For the past 10 years, Tom has helped architect Civil 3D into the leading AutoCAD-based civil engineering application. He has degrees in mapping, and civil engineering and surveying. His most recent side project at Autodesk has been the implementation of the DWG publishing extension for Google Earth, available on the Autodesk labs site and within Civil 3D.Using Google Earth with AutoCAD - 2 -Using Google Earth with AutoCAD - 3 - Introduction This class provides information on the two-way exchange of data between AutoCAD (and AutoCAD-based verticals) and Google Earth. This exchange of data is advantageous in numerous ways for your day-to-day design and engineering responsibilities. Several scenarios where this data exchange might be useful include: - Import imagery from Google Earth for use as a design back drop. - Import elevation relief data into AutoCAD to help depict as-built and proposed building designs relative to the surface terrain. - Publish map parcel information to Google Earth as a means of disseminating cadastral information. - Publish from AutoCAD to Google Earth temporal data for a phased construction project that can used by public agencies to depict how the project will impact residents. Where to find the Software Described in this Class The AutoCAD Google Earth publishing extension tool is available for free at Autodesk’s labs web site, http://labs.autodesk.com. Furthermore, AutoCAD Civil 3D 2009 includes the functionality described here-in. Understanding Google Earth’s User Interface This class utilizes several features within Google Earth extensively. There are numerous on-line guides to using Google Earth. Four that are highly recommended are: - Google Earth User Guide: http://earth.google.com/userguide/v4/ - Google Earth Blog: http://www.gearthblog.com/basics.html - Juicy Geography’s GE Blog: http://www.juicygeography.co.uk/blog/?page_id=5 - Google Earth Timelines: http://earth.google.com/userguide/v4/ug_gps.html#timelineUsing Google Earth with AutoCAD - 4 - Import Image from Google Earth To publish AutoCAD models to Google Earth, you must first be able to define the location of where the models are to be located on the Earth’s surface. This correlation of AutoCAD model space coordinates to Google Earth latitude and longitude coordinates is referred to a geo-referencing. A simple method of geo-referencing AutoCAD model space data is to import an image from Google Earth and position the image properly relative to your model data. Additionally, you can use the imported image as a backdrop for design. Prior to importing the image you should complete the following steps: - Start Google Earth, and zoom to the location on the Earth’s surface where you want to capture the image. - Zoom in close enough to capture the appropriate level of detail of the Earth’s surface in the area of interest. - Be sure you are looking straight down at the Earth’s surface (that is, the view does not have any tilt.) You can remove all tilt from the current Google Earth view by pressing the ‘u’ key. - Generally, it is best to keep the Google Earth application window maximized. Do not minimize or collapse the Google Earth application window. Now you are ready to bring an image of the Google Earth view into AutoCAD. - The ImportGEImage command is used to import an image from Google Earth. - After selecting the command, there will be a brief pause while the image is obtained from Google Earth. Then, a rectangle representing the border of the image will be attached to the AutoCAD graphics cursor. - Position the image to the desired location, and then specify a rotation angle to orient the image as desired, or - If AutoCAD Civil 3D 2009 or AutoCAD Map 3D 2009 is being used, and a map projection has been defined, you can select the option at the command prompt to position the image automatically using the map projection coordinate conversion algorithms.Using Google Earth with AutoCAD - 5 - Note the following items about the image import process: - Once placed, you may use AutoCAD’s move and rotate commands to further refine the position of the image relative to your model. Do not adjust the position of your DWG model. Rather, adjust the position of the image relative to your model. - The dimensions of the image in the drawing are defined by the extent of longitude and latitude the image covers in Google Earth and a transformation of those extents to the linear units defined by the INSUNITS system variable in AutoCAD. - If a map projection is active within Civil 3D or Map 3D, only the center point of the image is placed using the map projection transform algorithms. The extents of the image are still defined as in the previous item. - The image displayed in the drawing is an AcDbRasterImage, and is stored in the same folder as the DWG file. The first three letters of the image file name will be the same as the first three letters of the DWG file, and the file extension will be JPG. - The image entity has x-data attached that contains information about where on the Earth’s surface the image covers. This x-data is used to properly geo-reference the model space coordinates with the Google Earth coordinates. - The image brought into AutoCAD using this command will only be black and white, even though the image in Google Earth is in color. This is a limitation imposed by Google when using the Google Earth application programming interface (API). There is no way to change this. However, see the next section for a method to manually import a color image. Here is an example of an image of the Venetian Hotel imported to AutoCAD from Google Earth.Using Google Earth with AutoCAD - 6 -
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