| GIS & GOVERNMENT APPLICATIONS
Enhancing 911 Emergency Service
GIS program benefits from rubber sheeting rectification tool
By Doug Lierle Anyone who has ever called 911 during a crisis situation knows the value of this emergency telephone service. But even those who have benefited from the service may not be aware of or even remotely comprehend the extensive mapping, GIS, database management, and technological requirements of the system.
These requirements, which enable quick response to 911 calls and subsequent service to the point of emergency, are being enhanced considerably by MSAG Data Consultants, Inc., with headquarters in Orange, Virginia. Founded in 1988 for the sole purpose of providing local governments and their agencies with mapping, address, and database services necessary for enhanced 911 emergency telephone systems, MSAG's primary customers include both rural county and town governments.
MSAG's state-of-the-art GIS base mapping expertise has led the company into a full range of GIS-related services for existing and new clients around the country. Currently, MSAG Data Consultants has contracted with 45 emergency 911 and GIS clients.
Detailed geographic information systems for their 911 clients were developed using a suite of sophisticated software programs, including AutoCAD, MSAG's proprietary Eagle Map Locating System, and MULTRIC, a rubber sheeting program from Mentor Software, Inc. in Thornton, Colorado.
Inclusion of the MULTRIC system adds rubber sheeting capabilities to AutoCAD and AutoLISP, enabling AutoCAD operators to rubber sheet large tax/parcel/section maps to overlay base maps. All control points, regardless of the number, are honored exactly.
"The mapping service we provide our 911 clients normally starts with GPS surveyed ground control along with new aerial photography and stereo-compiled digital planimetric mapping at scales ranging from 1 inch equals 200 feet to 1" equals 600'," says Chris Haynes, GIS department manager at MSAG. "The major features typically captured include roads, driveways, buildings, fence lines, hydrology, tree lines, and utility lines." Haynes' primary responsibilities include project management, custom programming, system setup, and conducting needs assessments.
"After field checking the base maps, we add text attribute information such as road names, public building names, place names, and existing addresses. New street addresses are then assigned via computer using a county-wide addressing system. These addresses are assigned based upon road frontage and allow for future growth in the county without changing assigned addresses.
"After development of addresses, each residence in the county is notified of its address and information is collected pertaining to that residence, including name, phone number, old address, etcetera." Haynes continued, "This data is turned over to the phone company to assist them in converting their data over to the new addresses needed for 911 phone service. The end map product is the EAGLE Map Locating System, which is used in the county's dispatch center to pinpoint a caller's location over the digital base map and to provide the dispatcher with the geographic information needed to quickly route emergency responders to the caller's location."
According to Haynes, each GIS data layer as it is converted into digital form (either by digitizing, or scanning and converting) needs to be rectified back to the same geographic base map. For any GIS to be functional, its datasets must overlay properly to ensure that topological overlays and analysis can be performed in a reliable manner.
"We use MULTRIC extensively in this respect, especially in the conversion and rectification of tax parcel mapping," he says. "By electing control points that represent common features shown on both maps (i.e., road intersections, fence lines, etc.), the maps can be rectified to allow them to overlay properly. And while not normally used in the base map compilation, we have used MULTRIC to match existing address maps based upon TIGER files to our base mapping for the purpose of transferring map attribute data to the new base map."
One recent project in particular dramatically illustrates the capabilities of MULTRIC, which include the ability to deal with an unlimited number of control points. MSAG was contracted by Spotsylvania County, Virginia to perform 1"=200' planimetric mapping, adding address data from field collected locations, and to install the company's EAGLE Map Locating System in the county's dispatcher center.
The plan was to visit every residence in the county and collect the address numbers manually, an extremely labor-intensive task. If numbers were not posted on the residence, field crews would need to knock on each door in order to collect the data, or resort to other hard copy maps to identify the address.
"Instead," says Haynes, "we proposed to use existing digital tax parcel mapping and its associated property database containing street addresses to do the job. In order for this process to work, we needed to transfer the address data from each parcel to the correct building. By selecting 16,800 control points throughout Spotsylvania County at features identifiable on both the parcel maps and base maps, we use MULTRIC to perform a county-wide rubber sheet transformation to transform the existing 90 tax parcel maps with approximately 50,000 parcels.
"Because of the success of this transformation, we were able to transfer over 90% of the addresses in-house prior to going out in the field, resulting in a great reduction of time required to perform the field edit. The county will now have a more accurate and usable tax parcel database since it has been rectified to the 1" = 200" base maps and can now be overlaid to the base mapping. The EAGLE locating system should be installed in early 1998, and because of good, accurate data it will aid dispatchers in getting emergency responders to the point of call as quickly as possible."
According to Haynes, one of the primary features of MULTRIC is its ability to perform different rubber-sheet transformations of geographic data from within AutoCAD. There are seven different transformation types available, he says, and MULTRIC has "proven to be the best way to transform maps with inconsistent scale to an accurate base map."
MULTRIC uses a TIN (triangulated irregular network), creating a different transformation for each triangular face of the surface in order to model the data, unlike other systems that employ a power series approximation to transform the data. MULTRIC's method allows every control point picked to be honored exactly.
"This is not the case with other programs such as the power series that uses control points merely as weights, and best approximate a surface through the control points," says Haynes. "These types of transformations tend to be poorly influenced by inaccurate control points, whereas the MULTRIC transformation localizes distortion around a bad control point, allowing for easy editing of the data."
Haynes believes that one of the best features of MULTRIC is its ability to input control points in many different sessions and to perform rubber sheeting on a large county-wide scale. This, he says, allows edge matching of maps to be maintained while ensuring a consistent stretch across map tile boundaries.
"Most software expects the control points to be entered interactively in one session, which is impractical when tens of thousands of points are needed," Haynes asserted. "Another benefit is the ease of customization allowed through the supplied LISP programming functions. We were able to easily customize the software and add new functionality for control point entry and for batch processing of data to better match the way we do business, which includes putting MULTRIC through its paces under three different AutoCAD releases (12 for DOS, 12 for Windows, 13 for Windows) and four different operating systems (DOS, Windows 3.1, 95, and NT), and it has performed in an excellent, flawless manner." About the Author:
Douglas E. Lierle is president of Lierle Public Relations, a full-service PR and marketing agency with headquarters in Denver, Colorado. He can be reached at 303-792-0507. Back |
