Enterprise Location Referencing System – Transportation (ELRS-T)4. ELRS-T - Functional Requirements The scope of ELRS-T is limited to address two important functional requirements [1] of any Location Referencing System:
The ELRS-T would support the transformation of asset location among the Linear and Geodetic methods. The ELRS-T would support the sustainability of the location of the asset after any changes to the road network. Thus, the network can be regenerated to showcase the roads and incidents that were relevant to a particular time period. I. ELRS-T Datum - GIS Data Model The ELRS-T datum would be a combination of Linear and the Geometric datum of a region. Both the Linear and Geometric datum would be maintained in an RDBMS with spatial support. Besides location component, time and date of measurement are also collected to check persistence of the asset data and temporal analysis [1]. Linear datum comprises of anchor sections connected by two anchor points. The anchor section follows the logical centerline of the roadway, with anchor points being located along that centerline. Anchor points must have a unique identifier, location description/remarks, and real-earth location as their attributes. Anchor sections have mandatory attributes of a unique identifier, designation of terminal anchor points, and length. A Traversal in the linear datum can have many connected anchor sections, with their field measurements varying sequentially according to its arrangement. The density of anchor points determines the positional accuracy of the linear datum. The anchor section length serves as a quality check for the linear field measurements. The ability to detect and correct measurement errors varies directly with the number of anchor points and inversely with the average anchor section length [2].  Fig 1. Data Model Geometric datum is the cartographic (x,y) representation of the centerline of the road network. The geometric datum supports the transformation of asset location data from GPS to Linear Methods and vice versa. Geometric datum would assist in map analysis and reporting. Traversals in the linear datum and the geometric datum are tightly coupled by defining unique identifiers. In ArcGIS, the linear and geometric datum of a traversal are recorded in terms of a linear feature and a measurement along it. Instead of being composed of x,y coordinates, a feature’s geometry in ArcGIS can be composed of x,y,m (or x,y,z,m) values [3]. |