Take a quick survey among CAD and GIS vendors, and you'll find them hard at work creating products that make the two technologies more complementary. As both CAD and GIS have evolved, it's become necessary for mapping and design professionals to tap the strengths of both to manage increasingly complex challenges. At the heart of GIS and CAD integration lies this issue: Can professionals feasibly and cost-effectively access the data they need to resolve design problems and make sound business decisions based on GIS maps?
      Looking at the variety of software solutions that have emerged to achieve integration, the answer is a resounding Yes! Autodesk, the Sausalito, Calif.-based publisher of AutoCAD, has developed the AutoCAD Data Extension that runs as an AutoCAD ADS application and introduces many automated mapping functions that work directly in AutoCAD and with the .DWG file format. For addressing civil engineering's 3D digital-terrain modeling and high demands for CAD accuracy, Plus III Software, Atlanta, offers Terramodel, a 3D land-design tool that links to ARC/INFO GIS data.
      Also targeting the civil-engineering niche, Genasys, Fort Collins, Colo., has developed GenaCivil that runs with the company's GenaMap GIS or as a stand alone application. GenaCivil is an enhanced CAD interface for civil engineering and features TIN (Triangulated Irregular Network) terrain modeling that's preferred when high accuracy is required for working with small land areas. In an effort to treat CAD and GIS as one element, Intergraph, Huntsville, Ala., has incorporated its PC-based CAD product Microstation with its GIS software MGE Modeler and Framme, a software engine for distributed information systems in the utility industry. An update of its MGE PC, MGE PC2 is slated for a January 1995 release. Moreover, Intergraph has increased its software's openness by publishing the Microstation file format. This move ups the ante for which vendor can claim the highest level of open systems; most other vendors' formats remain proprietary, though some kind of programming interface or integration tool kit is typically provided.

The Urge to Merge
A vendor's background influences heavily the approach it pursues to achieve integration. Whether a CAD vendor is introducing GIS features into the CAD environment, or the opposite, a GIS vendor offering CAD features within GIS, the resulting hybrid software environments have come a long way in overcoming each technology's shortcomings. CAD's strengths have remained its double-precision accuracy and the ability to express complex curves and 3D geometry that until recently GIS systems could not. Yet, GIS has never been concerned with that high a level of accuracy and geometric constructs, and has instead focused on providing a topological data model that's unavailable in CAD.
      On the other hand, CAD systems quickly reach their performance limit when attempting to manipulate large map databases (some CAD systems, running without performance-enhancing applications, require as long as a half hour to load large files). CAD systems haven't matched the great variety of projections so prevalent in GIS, and users have had to settle for a sheet view of drawings and being able only to render profile or cross-section views. CAD system translators accomplished graphics translation to GIS, but what of accessing non-graphic attribute data (left behind by translators) that's critical to GIS analysis? These are some of the major differences between the two technologies that GIS and CAD vendors have sought to assuage. Let's now look at how CAD vendors have introduced GIS functions into their software.

AutoCAD Data Extension Enhances Automated Mapping
Any GIS professional crossing into the CAD arena will likely have to work with AutoCAD .DWG data since a lot of data are stored in this format. Since ADE works within AutoCAD, it allows users to bypass the translation bottlenecks when CAD data is converted for use in automated mapping. And, when GIS files grow in complexity, ADE permits more efficient management and access of large GIS files. Current AutoCAD users can immediately begin GIS work with a minimum investment, for ADE integrates with AutoCAD Release 12 with no additional system requirements.
      Choosing data locations from query dialog boxes and highlighting drawing sections with a window, points, or polylines are all straightforward functions in ADE. And users can further define location criteria by combining them with AutoCAD properties such as a layer, attribute, elevation, line type, block name, or area, among others. Productivity enhancements result when users can readily access only portions of drawings they need, and this selected data can be modified, analyzed and saved back to the drawing.
      Users will find in ADE these kinds of automated-mapping features in abundance, for the product is deliberately designed for GIS and CAD customers desiring simplified automated mapping rather than high-end GIS analytical tools. Users looking to manage assets and infrastructure with .DWG-formatted data will find ADE the ideal match. For more sophisticated analysis, users can transfer into ArcCAD, a GIS product from Environmental Systems Research Institute that links with AutoCAD.
      Another ADE feature addresses the problem of changing X-Y coordinate projections to map projections by providing more than 300 cartographic coordinate systems and a facility for converting projections. Presently ADE for AutoCAD Release 13 is under development and will take advantage of Release 13's object-oriented design, which could, in the long-run, permit ADE to create even tighter links between attribute data and entities. Also on the horizon is incorporating a topological data model into ADE. This would standardize the numerous topological data models that exist among AutoCAD GIS applications and bring AutoCAD and ADE even further into the GIS world.

Treating GIS and CAD as One Element
Intergraph, on another part of the CAD spectrum, was once a name synonymous with proprietary, turnkey systems. A sea-change in strategy two years ago at Intergraph resulted in the porting of its CAD and GIS software to Windows, NT, DOS and Intergraph's version of UNIX. That Microstation's file format is publicly available complements Intergraph's CAD and GIS integration, which is also bolstered by MGE Modeler, MGE PC and Framme incorporating Microstation. Now Intergraph's GIS users can benefit from CAD's high accuracy and directly access Microstation's CAD objects and geometry to achieve a more precise description of GIS data.
      Another Microstation advantage: it imports and exports AutoCAD .DWG data, enhancing Intergraph's GIS systems ability to accommodate data from many sources. Included with Intergraph's efforts to improve data integration are built-in tools for raster and vector integration, and it's Intergraph's view that GIS should accommodate both data types. Having this capability boosts performance for displaying in map form a mass amount of data quickly. Users looking to expand their GIS work on the desktop will find in MGE PC features for building SQL queries via using a simple interface.
      Like Autodesk, Intergraph provides links that associate attribute data stored in an external database to entities appearing in a CAD or GIS system, and Intergraph also has developed object-oriented techniques in its software. Object-oriented features permit a more powerful association of data elements; for example, if a user moves a line entity, other elements relevant to the line can move with it. Having examined CAD and GIS integration from a CAD perspective, a review of GIS vendors' integration efforts is in order.

GIS and CAD in Civil Engineering:
Bringing GIS into the 3D Realm
It's Plus III Software's view that for land-design applications, the CAD data model falls short because CAD models primarily use information needed to render a design for drafting, not information required to create the design. Moreover, the CAD data model doesn't support types of data that civil engineers use in designing, editing and analysis. This hinders extensions of CAD programs into area of 3D digital-terrain modeling (DTM) and ambitions to connect a DTM to GIS topology and attribute data.
      But applying a parametric 3-D surface modeler such as Plus III's Terramodel eliminates these barriers, enabling civil engineers to design and associate design elements in plan, profile and sheet views. Terramodel also supports a suite of civil-design applications: coordinate geometry, legal descriptions, contouring, profiles, cross sections, 3-D views, site design, hydrology and roadway design. Data capture in the form of photogrammery, GPS and data collectors is another feature.
      Another Plus III product, Terragration, links Terramodel's design tools with ARC/INFO data. Unlike vector-based CAD Systems, Terramodel is point-based, so data is accessible in much richer detail; according to Plus III, Terramodel provides civil engineers the ability to work with large data sets in excess of 1 million points. With Terramodel and ARC/INFO running concurrently, civil engineers who don't find the 3D functionality in some GIS systems adequate can process ARC/INFO data in a DTM model and apply tools such as coordinate geometry, site design, roadway design, sewer and storm water design, hydrology, surface modeling, and volumetric analysis.
      The result of Plus III's style of integration is sharing and linking attribute data, topology and 3D surface data all in the same software environment. Through its 3D ToolPak that enables third-party integration, Terramodel will soon work with other ESRI products, ArcCAD and ArcView. Terramodel operates on DOS and UNIX platforms, and a Windows release is scheduled for April 1995. Plus III also has more integration products on the horizon, including a link to ERDAS's Orthomax software that will allow stereo photography to be overlaid in Terramodel.
      Also in the area of civil engineering, Genasys's CAD/civil engineering interface with GIS called GenaCivil can automate data retrieval information relevant to a design, especially when engineers must accommodate a design to a surrounding environment. Traditionally, this process of gathering data from a design's environment remained separate from design work and has had to be done manually. Through GenaCivil's attributes database handling and links to relational databases, design-environment information can be collected more efficiently.
      An example would be the Federal Emergency Management Agency's digital conversion of its flood insurance rate maps. GenaCivil has proved instrumental in helping the agency generate new flood plain maps with greater speed and accuracy. GenaCivil's interface can search for data required for building the digital maps: bridge locations, stream channels and other data related to terrain.
      It's clear developments in GIS and CAD are working toward much greater efficiency for users who can benefit from combining both technologies. This will definitely ensure a wealth of solutions for professionals to choose from, and CAD and GIS users needn't feel encumbered by the lack of projection conversion or inadequate translations. Today's software solutions have resolved these stumbling blocks of the past. Vendors' introduction of object-oriented features have promise to introduce greater intelligence into CAD and GIS and enrich their capabilities to create thematic maps. From all indications, those looking to harness the productivity enhancements of CAD and GIS integration have a lot to look forward to.

About the Author:
David McGee is a freelance writer in San Francisco specializing in CAD and GIS applications. He can be reached at 415-826-1491.

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