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 , 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.
 |
 |
| Address Map Click on any of these screen shots to view full
size. |
The rubber sheeting program, MULTRIC, uses a TIN (triangulated
irregular network), which allows every control point picked to be honored exactly. The TIN
creates a different transformation for each triangular face of the surface in order to
model the data. |
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 Thomton, 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 I 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 correct 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.
 |
 |
Before - As a result of using a
power series program,
the streets in this map are out of alignment. |
After - Once the rubber sheeting process is finished, the streets
and other features are lined up. 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. |
"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."
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.
Chris Haynes
MSAG Data Consultants
P.O. Box 1307
Orange, VA 22960
Telephone: 540-672-0807
E-mail: msag@msag.com
http://www.msag.com
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