vehicle is on fire at a freeway interchange. The 911 center receives
a cryptic mayday message that includes a GPS coordinate. When the
crew arrive on the scene, they find the vehicle on the eastbound ramp,
not southbound as the message had indicated. Although they can see
the truck on the ramp below, it will take 20 minutes to loop around and
reach it by road.
The error in this case is
not in the GPS coordinate — with differential correction commonplace, that
is accurate to a couple of metres. The problem is positional disagreement
in the reference databases on which the coordinates are plotted.
The navigation system in the reporting vehicle snaps the coordinate to
one ramp. At the 911 center (which employs a different database)
the same coordinate snaps to another ramp.
Much of ITS hinges on communicating
the location of a vehicle, facility or event. The US DOT ITS
Program states: “One of the highest priority enabling standards identified
in the ITS America survey is that of Location Referencing.”
To make location referencing
unambiguous and error-free, two standards strategies must be pursued
simultaneously: coordinate standardization (addressed by the ITS Datum)
and messaging standards (addressed by the Location Reference Messaging
Specification or LRMS).
These two national efforts
constitute the core of the research agenda at VITAL. Our work
takes place in the lab, conceptualizing and critiquing, and in the
field, surveying points, testing emerging technologies, and talking
to highway workers in hard hats.
To enable field experiments,
VITAL's first task (January–July 1997) was to build an experimental
infrastructure for ITS testing, consisting of a mobile observation
vehicle in communication with a fixed server, and a set of street databases.
The basic infrastructure is now complete; it will be customized as required
to support specific experiments.
We have initiated work on Positional
Error. This will be ongoing alongside other testing, because
positional error issues are the centerpiece of our work. Most recently
the positional error research has culminated in solutions
In August–October 1997 we tested
the Cross Streets Profile (XSP), part of the
LRMS. The Profile was modified following our recommendations, and
we re-evaluated its performance in October 1997–March 1998.
In 1998-99 we evaluated the
Linear Referencing Profile (LRP). That
report is now available, and many of the findings will be of great value
to public agencies wrestling with location referencing problems and map
We have begun work on conceptual
development and testing of a local prototype of the ITS
Datum. More than 3000 points have been established around the
Santa Barbara urban area, and our rubber-streeting
algorithm can now demonstrate the effect of geometric correction using
the Datum. We are working with other agencies (NSDI and NCHRP) who
are also proposing national datums, to share ideas and to minimize duplication.
|Check here for
Technical Papers and Reports from current VITAL
research, and earlier NCGIA research in transportation.