Civil Engineering

Data to Design: Good Design Requires Accurate Base Maps

6 Jan, 2009 By: Lucy Kuhns,Marcia Carrillo

You have just won the latest infrastructure project and can't wait to get started with the design. But first, you must prepare the existing conditions base map. A complete, accurate base map is critical to the success of your project. The project team will need to research and include the usual existing condition boundaries, easements, and topographic, hydrologic, and infrastructure features. And, with today's safety, environmental, and sustainable design requirements, you will also have a wealth of other robust data that must also be included.

Including all of this often disparate data into your project base map can be a cumbersome experience, and when your base map is constructed with different data types, such as GIS, survey, imagery, tabular, and even legacy hard copy items, this can sometimes take more time than the actual design itself! Today vast amounts of robust data are available for our use. However, most CAD systems are not able to easily consume and directly use these data types in their CAD-based drawings. Many engineering professionals face the challenge of taking a CD full of CAD, GIS, survey, imagery, and miscellaneous project-related data and compiling it in order to get a base map prepared in time for a meeting with only a day's notice.

With the incredible amount of data available today in a variety of formats, the challenge is to get that data into your CAD base map drawing as accurately and easily as possible. Data conversion, coordinate system reprojection, and drawing cleanup can make this task laborious and time consuming. This article outlines how to use AutoCAD Map 3D 2009 to bring disparate data into drawings through its Feature Data Objects (FDO) data connection and how to use Map 3D’s built-in drawing cleanup tools to best prepare data for the design process.

Removing the Road Blocks
With Map 3D’s FDO connection, you can connect to all the different data types (such as SHP, SDF, JPG, MrSID, DEM, and point list files) for use in the base map drawing. FDO allows users to quickly gather information, such as center lines of roads, parcel boundaries, control benchmarks, soil types, zoning limits, contours, and high-resolution aerial photos.

Standard connection types include SDE, Oracle Spatial, raster (MrSID, GeoTiffs), WFS (web feature service) and WMS (web mapping service), as well as ODBC, MySQL, and SQL server. The FDO data connection tool is accessible from the docked Task Pane. Once loaded, the data can be symbolized and queried for display in the map model window. The Style Editor allows the data to be labeled, symbolized, and themed by any of the attributes that are associated with it.

Use the FDO connection in AutoCAD Map 3D to bring together disparate data types.

Working with Coordinates
When working with CAD systems, all the data must be in the same projection and coordinate system or it simply will not overlay correctly. Often the imagery, engineering, and GIS data are in different coordinate systems and even in different units. For example, the images might be in Universal Transverse Mercator (UTM), the engineering data in state plane coordinates, and the GIS data in a WGS latitude and longitude system. Units must also be consistent. Systems may be in meters, U.S. survey feet, international feet, or some other unit. The difference between U.S. feet and international feet may seem small (One U.S. foot equals 1.00002 international feet), but considering that the coordinate ranges for many systems are in the one- to two-million range for northing (y) and easting (x) location, this can result in errors of more than two feet!

To solve the problem of varied data with varied coordinate systems in AutoCAD Map 3D, you apply a global coordinate system to the base map drawing. Knowing the main purpose of your base map drawing, you can choose an appropriate coordinate system and units. For example, if your project is an engineering or infrastructure development project (any project that will require construction), typically the global coordinates are set to the location's state plane zone. Once the global coordinate system is set, any other data will be reprojected on the fly to conform to this system, and dissimilar units will convert as well. Another helpful feature is that coordinates can be set within AutoCAD Map 3D's data connect window, allowing easy integration for data that doesn't have a projection file associated with it. For example many ESRI shape files come with no projection (PRJ) file, which means they do not automatically "know" what coordinate system or units that they are in. To solve this in AutoCAD Map 3D, select the coordinate system that you think the data was created in for use in that system. To accomplish this without using this Map 3D feature, you would have to use ESRI's Arc Catalog or would need to create your own PRJ file in Notepad.

Dealing with Hard-Copy Data
Many times during the base map creation you will need to incorporate hard-copy data from legacy drawings, plats, and legal descriptions. These typically need to be scanned for heads-up digitizing, which can take a considerable amount of time, then checked for accuracy. Autodesk Raster Design can be used to scan and then vectorize selected image components.  For example, you can digitize the contour lines from scanned hard copy map image by using the Contour Follower tool, which allows you to convert scanned contour maps to polylines with elevations. Select the major and minor contour line in the raster image and the contour follower will trace the line, create a vector contour line, and assign the elevation in Map 3D.

Getting Site Survey Data into Your drawing
At the onset of a project, preliminary site survey data is collected and needs to be added to the base map drawing. Usually this data is in a point list format or a comma- or space-delimited ASCII text file. Many CAD users find this difficult and prefer a third-party software to help with the task. AutoCAD Map 3D offers a survey tool kit that supports LIDAR and other data formats (x,y,z format) and can be integrated into the drawing and visualized for site verification. The survey toolkit also allows you to load LIDAR and point data files to create 3D surfaces and contour lines.

Survey data file inserted and surface contours created.

Managing Drawing Change and Clean-up
Once the preliminary base map is created and approved, changes or updates often need to be made. The data connection feature enables drawing clean-up and multiuser editing of DWG files, and more than one engineering professional can be editing a drawing at any given time. This accelerates the base map development time and when used in conjunction with the drawing clean-up tools, can reduce the cost of base map development changes.

Full base map ready for design.

Ready for Design
Once all the data is cleaned up and displayed in Map 3D, you can move on to the design process using the AutoCAD design tools inside Map 3D, or you can open your project drawing in AutoCAD Civil 3D. You can also export data for use in other design applications, or you can simply push data back to a GIS source.

Related content:AEC, AutoCAD, Civil Engineering

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