DOT Develops Robust Enterprise Geospatial Repository
Continued...
UNETRANS UML Database Model Modifications
VDOT identified various useful techniques while extending the UNETRANS model. The following tables were added to the model:
- Anchor Section Type Table
- Anchor Section Measurement Table
- Measurement System Type Table
- Route Anchor Section Begin Measure (optional)
- Anchor Section Measurement Change Table
- Anchor Sections in Routes Table
- Anchor Section Change Table
Set Field Properties with Tags in the UML Model
The first change made in the model was to add an attribute tag to set the length of all the string fields to more appropriate values for VDOT data. An attribute tag for the field name was set to an alias to make it easier for end users to correctly fill in the field. The attribute description field documents general information about the use of the field, where to find values for the field (especially useful for existing legacy data), and any domain sets of valid values.
Add VDOT-Specific Domain Tables in the UML Model
To limit and validate data during entry, domain tables were customized or added by VDOT. The measured feet and measured miles domains were set up to automatically retrieve the geometric split of these length values any time a road segment was split during editing. Separate domains were created to allow a different valid range of values for each, although both had the same split and merge policies.
Use Subtypes for Conditional Topology Network Rules
Topology rules allow the use of only subtypes to model conditional rules. For transportation networks, the rule "Lines-must not have dangles," is of particular interest. Cul-de-sacs are the exception to this rule. These features can be modeled using the intersection subtype. No line road subtype conditions were identified at this time so no subtypes were created for the road table class. The intersection subtypes were modified to add additional subtypes for "Brunnel," "Boundary," and "Not Stated/Not Applicable."
Stable Node and Segment IDs
To keep node and segment IDs stable, these IDs must be unique statewide and cannot be modified. The ObjectID field is the only automatic ID field allowed by ArcGIS geodatabases. However, whenever a table is copied or exported, this value can be set to a new value and made unique in the new environment. Consequently, Esri recommends that a new field be created and managed by the user/application to link business data and ensure that IDs are unique. In the UNETRANS data model, the TransportEdgeID and TransportJunctionID fields were used for the road and intersection tables, respectively. These IDs were converted to numeric integer fields to improve performance with large datasets and control source data.
How to Track Historical Records/Archive Edits
After concluding ArcSDE versioning was not appropriate for handling historical archiving, VDOT began implementing its own archiving strategy using a custom class, ArchiveClass, it created. The data model was duplicated so each edit table would have an historical archive table for storing the previous states of the features and attributes for effective beginning and ending dates. Separate tables were created for feature datasets and separate tables for related attribute tables. To save the baseline, all added or current records were moved to the historical table. Any new features added were also moved to the history table. The initial record will have a bogus default 2099 effective end date.
Roadway Network System
The success of VDOT's initial efforts has created new opportunities for the department. The legacy Highway Traffic Records Information System is being migrated to Oracle with a Web-based spatial and data editing application called the Roadway Network System, and the UNETRANS model has proved a great foundation for this effort.
External consultants reviewed the modifications VDOT made to the UNETRANS model and indicated that UNETRANS will provide a good foundation for continued performance refinements in editing transactions and map presentation. For more information, contact
Dan Widner, GISP
Information Technology Applications Manager
Virginia DOT
Tel.: 804-786-6762
About the Authors
Dan Widner is an IT applications manager for VDOT where he oversees the agency's GIS program and roadway spatial information systems. He has 25 years' professional experience in mapping and GIS serving in the public sector, at federal and state levels, and in the private sector with a GIS software firm and an IT consulting firm. He holds a bachelor's degree in geography from Indiana University. He can be contacted at Dan.Widner@vdot.virginia.gov.
Paul Bucher is a senior principal consultant with Keane, Inc., and technical team lead for the development of VDOT's Roadway Network System. He has held various consulting roles at VDOT related to enterprise architecture studies and strategic plans, and he understands the need for robust spatially enabled application systems for transportation. He can be contacted at Paul.Bucher@vdot.virginia.gov.
|
