GPS2CAD

This issue of the AECbytes product review takes a break from the traditional realm of AEC software to look at a different kind of application. GPS2CAD, as its name suggests, allows the points recorded on a GPS (Global Positioning System) unit to be automatically plotted into a CAD application. Since a recreational-grade GPS unit costing around $100 can be used to collect the data and the price of the application itself is $345, GPS2CAD becomes an easy and inexpensive alternative to a professional survey-grade system for collecting and plotting field information. Its scope extends well beyond building design to landscape design, civil engineering, power and process plants, GIS, mining, and so on. For building design in particular, it can be used for surveying the site and marking specific points of interest that would be relevant to the planning of the project on the site. (It should be noted that recreational-grade GPS units are limited in their accuracy, so the user has to ensure that the accuracy is sufficient for the task at hand. Boundary work or building layout wouldn't typically be done with a handheld GPS.)

Let's see how GPS2CAD works .

Plotting the Points in a GPS Unit

The first step would be to take the GPS unit to the site and plot the data that is of interest. The unit I used to test GPS2CAD was eTrex from Garmin (see Figure 1). Once you turn it on, the unit connects with satellites to determine your exact location. You can then move to specific positions within the site and mark them on the GPS unit as a "waypoint," which is the term used to denote a point of reference in GPS terminology. You can associate a name and a graphic symbol with a waypoint when you save it. There is a limit to the number of waypoints that can be saved, which differs from unit to unit; for the eTrex, the limit is 500.

Saved waypoints, up to a maximum of 50, can be linked together to form a "route." While routes are primarily navigational aids that guide the user to move from one location to another when large distances are involved, they can be recorded and independently loaded into GPS2CAD for specific uses. In addition, the GPS unit also records automatic "track points" as you travel from one location to another, without the need to mark waypoints. The eTrex allows up to ten such separate tracks to be stored. Again, tracks are primarily used as a navigational aid, but can be imported into GPS2CAD as well for subsequent translation to CAD.

Once the GPS2CAD application is installed, you can connect the GPS unit to the computer and load the waypoints that were saved into the application. The waypoint information appears in the table grid to the left of the application window; Figure 2 shows a set of 9 sample waypoints I had marked in my unit and uploaded into GPS2CAD. For each point, detailed information such as latitude, longitude, symbol, and so on can be seen. With regard to altitude, most GPS units cannot calculate that accurately since they are working from satellites, so they typically do not maintain altitude data of waypoints in their database; this is why the Altitude value appears as 0.000 for all the waypoints in Figure 2. (However, newer and more expensive GPS units have built-in barometric altimeters and can provide accurate elevation recordings.) The X(Easting), Y(Northing), and Zone values in the table are the calculated coordinates of the waypoints based on the datum and units specified in a Setup dialog of the application. For the example shown in Figure 2, the UTM NAD 27 datum used in North America has been specified. This datum converts to U.S. feet. (For more on datums, please see this USGS site.)

A second grid, Direction and Distance, on the right of the Waypoints grid shows the azimuth in degrees and the distance between each point and its subsequent point. A Units drop-down list lets you specify which units should be used to indicate the distance. The example in Figure 2 uses miles, indicating that the total distance from Point 001 to Point 009 is nearly 0.45 miles.

You can now select one or more points from the Waypoints grid and see them in an actual map. Four types of maps are available in GPS2CAD: a Preview map, which shows the selected points as a simple line-plot with labels; an Aerial Photo, obtained from TerraServer-USA, which provides public domain mapping of the United States and selected territories; a Topo map, also from TerraServer USA; and a Tiger map, also known as a Census map. Because of some restrictions, only one point at a time can be displayed in a Tiger map; however, it is more flexible with display scale, allowing more choices than the Aerial and Topo maps. Figure 3 shows all the 9 sample waypoints correctly appearing in the Aerial photo of the area in which I marked them on my GPS unit. The map with the points can now be saved as an image file, if required, for use in another application.

The map window of GPS2CAD, shown in Figure 3, has various options for zooming, scrolling, specifying the marker shape and color used to plot the points on the map, and so on. One critical option here is the ability to add additional points to the data set by simply clicking on these points in the map. The relevant data such as latitude and longitude of the point is automatically captured. Thus, it is actually possible to use GPS2CAD for deriving point data for any site in the US without using a GPS unit at all?you simply need to know the approximate latitude and longitude of the place to bring up its TerraServer maps, and then zoom in more precisely to the desired location.

Back in the main window of GPS2CAD shown in Figure 3, points can be added, modified, or deleted, and the entire set can be uploaded back into the GPS unit if required. It is also possible to use the application in real time, by connecting the computer to the GPS unit as you navigate through the site and mark waypoints. The application works with routes and tracks in a similar fashion to how it works with waypoints.

Exporting the Data to Other Applications

The final key component of GPS2CAD is its ability to plot the data directly in AutoCAD and export it into different formats for use with other applications. Let us look at its interface with AutoCAD first. The application is designed to work with AutoCAD versions 14.01 through 2004; I tested it with Autodesk Architectural Desktop 2004 and found that it worked with that as well. You need to launch AutoCAD or ADT, and open a new or existing drawing. Then you go back to GPS2CAD, specify the basic settings for AutoCAD layer, color, and scale in a dialog, select the waypoints, route points, or track points that are of interest, and select the Plot Lines command (which can be seen on the top toolbar in Figure 2). If you now return to AutoCAD, you can see the lines connecting the points in the drawing. Figure 4 shows the ADT 2005 line plot for the same test set of 9 waypoints shown in Figures 2 and 3. The points are all plotted at elevation 0; the application does not yet have the capability for 3D plotting. It is also possible to plot the GPS2CAD points as points or blocks in AutoCAD instead of lines, and an upcoming version of the application will allow these to be plotted in 3D. There is two-way link with AutoCAD, which allows you to makes changes to the point set in AutoCAD and upload them back into GPS2CAD.

In addition, GPS2CAD can export the point data to text files, Access 2000 files, and DXF files, allowing most technical and CAD programs the ability to use it.

Real World Examples

While I used GPS2CAD for a relatively simple plot, it can be used by architectural and engineering firms for surveying and marking points on complex sites. Figure 5 shows an example from Fletemeyer & Lee Associates, Inc., a Colorado-based architecture, landscape architecture, and planning firm that uses GPS2CAD to transfer points taken in the field to constructed topographic surveys showing specific points of interest, views, building locations, trails, roads, etc., for master planning purposes.

Another example, shown in Figure 6, comes from RDK Engineering, a Pennsylvania-based civil engineering firm. Prior to the use of GPS2CAD, the firm had to carry out site surveys manually; it finds the application a lot more efficient and accurate and uses it extensively.

Considering the simplicity and ease of use of the application, it is no surprise that GPS2CAD works as a great educational tool for teaching about GIS, GPS, and CAD. A high school in Utah, Gunnison Valley High School, has found GPS2CAD an exciting component of its CAD curriculum. One of the assignments the students worked on with GPS2CAD was to mark out the school's football field in a GPS unit, download the coordinates into AutoCAD, create a design in AutoCAD for the field, get the CAD points back into GPS2CAD, upload them to the GPS unit, and then go back to the field to mark the design. The next project is to create a corn maze using the same method. The school also worked on a real-world project with GPS2CAD with a local irrigation company, which had just built a new large settling pond and needed to figure out its surface area. The shape of the pond made it difficult to survey and measure. A handful of students marked the pond using a couple of Garmin GPS units and downloaded the waypoints using GPS2CAD into AutoCAD. It was very easy in AutoCAD to then create the drawing and determine the data the irrigation company needed. This gave the students a very practical experience of the use of this technology.

Conclusions

GPS2CAD is a nifty application that is an inexpensive alternative to the use of high-cost professional survey-grade systems for collecting and plotting field information. It is simple enough to be used by architects and engineers in-house for conducting site layouts when handheld GPS accuracy is acceptable, instead of sourcing it out to external surveyors. Being able to plot the collected data directly into AutoCAD is a big plus. The current inability to plot the correct elevation of points is definitely a limitation, but not serious enough to detract from the overall usefulness of the application.

About the Author

Lachmi Khemlani is founder and editor of AECbytes. She has a Ph.D. in Architecture from UC Berkeley, specializing in intelligent building modeling, and consults and writes on AEC technology. She can be reached at lachmi@aecbytes.com.

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