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AutoCAD

Harness Google Earth Tools in Civil 3D 2008, Part 1 (CAD Clinic: Civil 3D Tutorial)

30 Jun, 2007 By: Mike Choquette

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How to bring Google Earth terrain and image data into Civil 3D.

For years, the Internet powerhouse Google has collected and served geospatial data from all over the world. This massive library of street mapping, satellite and aerial photographs, digital terrain model data and more is available for browsing through a free utility called Google Earth. Although Google Earth is similar to other online mapping systems such as Microsoft's Virtual Earth, there is one big difference -- Civil 3D 2008 can import terrain and image data directly from Google Earth, as well as publish its own 3D data for viewing within the Google Earth utility. Some of these tools were available in the Technology Preview Google Earth extension for Civil 3D 2007, but the under-the-hood functionality in 2008 has matured quite a bit. Everyone who uses Civil 3D should be familiar with this extremely useful feature set.

The Disclaimers
The geospatial data Google Earth provides isn't unique -- a tremendous amount of GIS (geographic information system) data is available for free or at relatively low cost. Many government agencies host Web sites where you can download the same imagery and terrain model data that Google Earth provides. The advantage to using Google Earth is that you don't need to dig through the often-confusing data indexes used on GIS sites or browse through pages and pages of downloads to locate the data you want. All you need is an address or latitude/longitude value, and Google Earth can find data for you.

A word of caution, though -- the free version of Google Earth does not offer as high-quality data as you may be able to find on those other GIS Web sites. You must use the terrain models, especially, with caution because they are nowhere near survey grade. They are probably best used in visualization and large-scale mapping, view-shed studies and (for the brave) rough conceptual designs.

Before using Google Earth and Civil 3D 2008 together for the first time, make sure you have the latest version of Google Earth and all the service packs available for Civil 3D. As of this writing, Civil 3D 2008 (service pack 0) works best with Google Earth version 4. If you downloaded Google Earth before January 8, 2007, you most likely have version 3 and should upgrade.

Also, if you intend to have the Google data overlay existing drawing data, it's best to have your drawing assigned to a real-world coordinate system. I'll look into this topic more in next month's "CAD Clinic: Civil 3D" article.

Locate Data in Google Earth
The process of bringing Google Earth data into Civil 3D is fairly simple. Launch both Civil 3D and Google Earth. If you know the address of the area you're interested in, type it directly in Google Earth's Fly To field. You also can search for an intersection such as "Weare & Beard Road, New Boston, New Hampshire".

If the area you're interested in doesn't have an address, you can also key in a latitude and longitude value (as decimal latitude, longitude) in Google Earth's Fly To field. If you aren't sure of your project area's latitude and longitude (and the drawing is assigned a real-world coordinate system), the map coordinate tracker can help. Inside Civil 3D 2008 choose Map/Tools/Track Coordinate Systems. Set the Track Coordinates utility to display latitude and longitude by pushing its Select Coordinate System button and choose the LL84 zone (the World Geodetic System 1984 datum, west negative). As you move your mouse in the drawing area, the Coordinate Tracker should provide decimal latitude/longitude information in real-time. Note that the tracker lists longitude (x) above latitude (y).

To make Google Earth's display more detailed, you may want to turn on some of the available data in the Layers area, such as political boundaries and roads, which appear with labels in Google Earth. These graphics will be included in images imported into Civil 3D as well. Pan and zoom in Google Earth's map display with your mouse buttons to the approximate coverage area you want to show in Civil 3D. Some advice for new users: In Google Earth, pan in with the left mouse button rather than holding down the wheel button because holding down the wheel button and moving the mouse rotates the view into 3D. In my testing, 3D-rotated images don't import into Civil 3D as expected (but they are fun to look at). If you aren't sure exactly what coverage you need, take your best guess -- it's easy enough to repeat the process if you aren't happy with the results.

Import Google Earth Data into Civil 3D
Before importing the data, be sure to maximize the Google Earth window to make your imagery as high resolution as possible. When ready, in Civil 3D choose File/Import/Import Google Earth Image, Import Google Earth Surface or both. At the Command line, accept the current coordinate system or choose another, and the data should instantly appear inside your drawing. If you haven't assigned a coordinate system under Drawing Settings this prompt doesn't appear.

Imported Google Earth images are created as JPEG files under your Windows profile and are automatically attached to the drawing. The default location (C:\Documents and Settings\USERNAME\Local Settings\Application Data\Autodesk\C3D 2008\enu) is most likely going to cause headaches if other users need access to the image, so I suggest changing the image location as soon as possible.

Surfaces imported from Google Earth appear as full-blown Civil 3D terrain models. If you import an image and surface at the same time, the surface automatically has the image draped over it. This means that if you display the triangles in Realistic display mode, the raster image appears on the surface in the correct location, even in 3D.

Surface draping is a new utility in Civil 3D that you can also manually apply through Surfaces/Utilities /Drape Image). You can change the display mode to Realistic (and also back to the default 2D Wireframe mode) through the Shademode command.

Summary
Google Earth provides a free, very easy-to-use way to import aerial and satellite images into Civil 3D drawings, as well as to approximate (nonsurvey grade) terrain models. Although the quality of the imported data may not be as high as what you can download from GIS Web sites, the ease of which you can use these tools makes them extremely valuable. They can be particularly helpful in the early phases of design when there isn't much other data available. In next month's "CAD Clinic: Civil 3D," we'll review working with coordinate systems in Civil 3D and look at the Publish to Google Earth tools.