Enterprise Location Referencing System – Transportation (ELRS-T)


The ELRS-T datum is illustrated below:


Fig 2. ELRS-T Datum for a Traversal


II. Components of ELRS-T

The components of the ELRS-T are

  1. Projection Module


    2. The function of projection module is to project the Geodetic co-ordinate (Latitude and Longitude) to the x,y of the underlying co-ordinate system of the geometric datum. Though the module would be irrelevant if the underlying geodetic datum is WGS 84, it is best to retain the native projection adhered by the country for map analysis.

  2. Linear Referencing Module:

    3. The functions of this module are

    1. To retrieve the measure (m), given the geometric co-ordinate (x,y) and the traversal .
    2. To retrieve the x,y for a given measure(m) and Traversal id
    3. To create point/line event tables for asset or incident location to enable map analysis and reporting (Dynamic Segmentation).
    4. To overlay two event tables to create an output table that represents the union or intersection.
  3. Address Geocoding / Reverse Address Geocoding


    4. Address Geocoding is the transformation of the street address to x, y and m along the linear feature. On the contrary, the reverse geocoding would convert the given x, y into a street address.

  4. Point Snapping


    5. The function of this module is to snap a point location (x, y, traversal) say, a GPS Co-ordinate or a geocoded street address to the nearest location on the traversal in the ELRS-T datum.

III Process Work flow – GPS to Distance Past RM Method

This section exemplifies the transformation of an asset data measured using GPS (Geodetic method) to Distance past Reference marker method.


Fig 3. GPS to Reference Marker (Linear) method


  1. Projection of Latitude and Longitude of the asset data into x, y of the Geometric datum
  2. Snapping the projected co-ordinate to the traversal (x’,y’)
  3. Query and Retrieve the measure ‘m’ at x’,y’.
  4. Query and Retrieve the reference markers on the traversal. Delineate the Reference marker with the nearest measure m.
  5. Compose asset location in the schema of the reference marker method.
IV Persistence of asset data

The road networks in the transportation are dynamic. New roads are being added, existing roads are extended and realigned, and old roads are demolished or abandoned [4]. Therefore, it is imperative to regenerate the network that existed at a particular time period. Hence, each traversal in the ELRS-T datum has to be marked with the time stamps indicating their service time period.

Each traversal is marked with a start date and the end date. Hence, if a traversal is altered, the altered traversal record is added in the table with its start date (date of operation). The original traversal record is closed with end date same as the begin date of the altered traversal. Each road asset or the incident data is collected along with time stamps for temporal match with appropriate network history.


Fig 4. Persistence of Asset data


5. Economic Benefits

The incorporation of GPS method in the legacy applications will prove to be more expensive as it involves reconfiguration and rework on the system. However, the available of ELRS-T would enable the legacy applications to convert to the GPS into a linear data and store in it for subsequent analysis and reporting. The ELRS-T would facilitate the definition of more reference methods such as navigation/dynamic objects for building dynamic transportation applications (ITS). Also, the ELRS-T can be extended to work for other federal utilities like waste and waste water pipelines, Gas Pipelines and many others.

6. Summary

The concept of the ELRS-T is the outcome of Enterprise GIS and ability to maintain conventional file based GIS formats in to RDBMS with spatial relationships. The ELRS-T is an enterprise GIS where multiple transportation applications can derive network information from it. The proposed ELRS-T has addressed only two concepts of a Location Referencing System. There are other issues like propagation of errors and definition of new reference methods. However, those concepts require new routines and additional procedures and triggers in the ELRS-T datum.

References

  1. Teresa M. Adams, Nicholas Koncz and Alan P. Vonderohe (2000) ‘Functional Requirements of a Comprehensive Transportation Location Referencing System. Proceedings of North American Travel Monitoring Exhibition and Conference.
  2. Al Butler’ Transportation Networks in ArcGIS: An Alternative to Geometric Networks.
  3. ESRI Technical Paper (2003) ‘Linear Referencing in ArcGIS®: Practical Considerations for the Development of an Enterprisewide GIS’
  4. Intergraph Mapping and Geospatial solutions (2004) ‘GeoTrans Transportation Data Model’.
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