University of California, Santa Barbara
|Overview||The second User Requirements workshop was held June 29-30 1998 in Santa Barbara. Predictably, it was difficult to find agreement on every detail among the 40+ participants, on how the Datum should be conceptualized, designed and administered to satisfy the entire range of requirements. Nevertheless, the workshop achieved its purpose, which was to help crystallize our understanding of what the user requirements were, and it has helped us (at VITAL) to focus our research agenda.|
|Visions||There are three, somewhat
divergent views of the Datum.
It could be argued that in a cost- and benefit-sharing environment, the most useful design is one that accommodates the needs of all stakeholders (in algebraic terms, the union of needs). Since the range of users is wide, this view of the Datum would for practical purposes be an accurate public sector database. This option requires a large up-front investment.
Alternately it could be argued that the first incremental step should be to build the component that is common to all stakeholders (intersection of needs), and that the components peculiar to one or other interest group should evolve as they are able to justify themselves. This option may serve nobody's interest in the short term, and leaves open the possibility that the needs of some stakeholders will never be met.
|.||Clearly, if the Datum is to be a reference framework for centerline databases, at least in the short term, then it would be appropriate to design it with reference to centerline error rectification, with associated assumptions about scale and error tolerance.|
|Agreement||There appears to be agreement
on a few core issues:
The ITS Datum consists of points and lines.
The points are variously termed nodes, anchor points, tie-points. (Proponents of the term “node” see the datum as a navigable network; proponents of the term “anchor point” do not). “Tie-point” is a neutral term to permit the discussion to proceed without getting bogged down in that controversy.
Similarly the lines are variously termed links, anchor sections, tie-lines.
seems to be agreement that tie-points must lie at physically recoverable
locations on the street network. What is yet unclear is the resolution
to which those points are defined and recovered. If 3-5 metres is
sufficient, then it is adequate to define a point as “intersection of Main
and State” (assuming that the center point of the intersection is reasonably
well defined). If sub-metre resolution is required, then the definition
may have to rely on a reference marker, a stake in the ground or
a brass marker in the vicinity of the intersection, relative to which the
tie-point is defined.
needs and concerns, so that future technical directions are rooted in reality and utility.
|There are points
of contention even at the highest level of conceptualization of the Datum:
or a skeleton of monuments and linkages, highly accurate data on a subset of the national street network, with increasingly comprehensive coverage at lower levels
or is it misleading and causing confusion?
Top down (national coverage the most accurate, as in geodetic datums) ...
or bottom up (national level the coarsest, increasingly accurate at local levels)
Recommended practice (and testing) of the administrative mechanisms to make it work successfully