Avatech's AutoCAD Google Earth Connector1 Mar, 2006 By: Dennis Wuthrich
Avatech's new Google Earth Connector for Autodesk's AutoCAD allows architects and engineers to tap into the simplicity of Google Earth's interface to communicate new designs in a true spatial reference system.
Editor's note: This review appeared originally in Cadalyst's sister publication, Geospatial Solutions (www.geospatial-online.com).
A lot of ink has been spilled in the geospatial community about Google Earth. I think it's fair to say that Google Earth represents one of the most exciting and interesting developments for GIS practitioners in the past year, and it's only appropriate that we discuss its relevance to our profession.
However, I also find it very interesting that we GIS people aren't the only ones taking notice of Google's new geospatial exploration system. All across the business landscape, people seem to be looking at the role that Google Earth might play in making complex information more accessible. Perhaps unsurprisingly, our brethren in the architecture, engineering, and construction (AEC) industry appear to be at the front of this charge.
Architects, civil engineers, and construction managers make a living designing and building complex structures such as office buildings, stadiums, roads, and housing developments. Much of the design and visualization of such construction projects is done using computer-aided design (CAD) tools. Such CAD products as AutoCAD and Microstation have served the AEC industry admirably for years. Both are excellent design applications, and each has spawned a wealth of sophisticated rendering and visualization tools.
A major benefit of Google Earth is the use of extensible markup language as a means of encoding geographic data.
AutoCAD and Microstation both support coordinate systems. However, neither requires the use of a true spatial reference system. Consequently, construction projects are often designed using project coordinates. From the perspective of an architect, perhaps a precise three-dimensional coordinate space is enough to design a new baseball stadium. But designing a new baseball park and getting a community to approve the stadium are two different things. These days, it's essential that large construction projects build broad support from a number of stakeholder communities. Communicating the design through a visualization technology is a required step in larger construction projects. Sometimes, building the ballpark hinges on depicting the new stadium as it might look relative to the rest of the neighborhood. This is where Avatech, a solution provider to the AEC industry, sees an interesting role for Google Earth. Architects and engineers are increasingly looking to share their designs with interested parties using the simplicity of Google Earth's interface, but tapping into that interface means georeferencing structures that are designed using project coordinates and encoding the geometry of the design in Keyhole Markup Language (KML), Google's openly published interface.
Avatech Solutions is an Autodesk value-added reseller that has served the manufacturing, building design, civil engineering, and GIS markets with CAD software and targeted solutions since 1997. With a background in the architectural, building systems, civil engineering, and mapping industries, Avatech saw a chance to test whether Google Earth might support the needs of their client base. Thus was born ExtractKML, Avatech's Earth Connector add-in for AutoCAD 2006 and 2005 that creates the KML necessary to place CAD objects onto the Google Earth globe.
According to Matt Mason, Avatech's director of research and development, the company's GIS developers showed the initial interest for creating a means of exporting AutoCAD models to KML for inclusion in Google Earth. The company's developers quickly realized that the key to a successful AutoCAD–Google Earth connector would come down to georeferencing structures and data that were created with project-based coordinates.
Georeferencing XREFs. ExtractKML is a freely downloadable software component for AutoCAD 2005 and 2006. Although Avatech's Web site still lists the software as "beta version 0.9," Mason assured me that the downloadable file is, in fact, ready for prime time as version 1.0. With his blessing, we tested the 2.8-MB executable using AutoCAD Map 2006. We found that it installed itself cleanly and without fuss.
Once installed, ExtractKML can be invoked as a command like any other in AutoCAD. Invoking the command launches a wizard that guides the user through the essential steps to create a georeferenced KML file. In theory, ExtractKML could be run from within any AutoCAD model, making it possible to create KML for just about anything you can create with the software.
However, there are a few house-keeping steps that must be attended to before building the KML file. First, Avatech's ExtractKML command is limited in its support of geometric entities. Only three-dimensional faces, lines, and polylines are supported. Because Earth Connector only supports a limited number of element types, and only in the current model, you may need to perform several additional steps to make the drawing ready for extraction. These additional steps include binding/inserting all XREFs into the current model. What's more, you'll need to run the explode command on AutoCAD entities (such as blocks, regions, and certain objects).
Figure 1. Georeferencing an AutoCAD model requires identifying the latitude and longitude of the project coordinate system's origin. ExtractKML supports this operation by importing a Google Earth placemark file. The user simply navigates to the project origin using Google Earth and digitizes a placemark.
Once the model has been simplified, the architect or engineer will need to orient the structure within Google Earth's spatial reference space. Avatech developers chose a very simple method for orienting AutoCAD models in space. In effect, Earth Connector uses a three-point method for georeferencing the model. As a first step, the user needs to identify the latitude and longitude of the project coordinate system's origin. Earth Connector supports this operation by importing a Google Earth placemark file. The user simply navigates to the project origin using Google Earth and digitizes a placemark (see Figure 1). A second point is required to define the orientation of the project's y-axis, and a second placemark file may be used to define this point. Alternatively, the user may define the heading of the axis (see Figure 2). Once the y-axis orientation has been defined, the software calculates a third point on the orthogonal x-axis. This is simple, and generally accurate enough.
Figure 2. Users can "georeference" a model in several ways. Once the project origin has been defined, the user may load a second placemark file to define the orientation of the model's y-axis. Alternatively, a compass heading can be entered.
Based on our testing, ExtractKML worked as advertised. Unlike many first releases of software, Earth Connector came with a very simple and useful Web-based help file that clearly and concisely summarizes potential uses and capabilities of the software.
As a freely distributed software component, I expect to see many in the AEC community incorporate Earth Connector into their model-visualization workflows. I also expect user demand to help guide Avatech's future development efforts for the product. In fact, Avatech's design approach for Earth Connector makes sense: Offer a very simple tool to the AEC community to test the demand and functional requirements for connecting with Google Earth.
All in all, Earth Connector is a very simple-to-use software application aimed squarely at the competent AutoCAD user who works in the worlds of architectural design and civil engineering. For the GIS community, most GIS folks will find that version 1.0 of Earth Connector is probably too restrictive for geospatial data. At a minimum, we'll need to wait for support for polygons. Nonetheless, Earth Connector does deliver on its promise to quickly transform three-dimensional structures into KML, no mean feat for many in the AEC community.