For any utility co. most critical requirement is a complete updated inventory of its assets. Any attempt to correct the network data at a later stage cannot result the desired sub-foot accuracy due to ever changing network and ongoing maintenance activities. The main aim should be to find a permanent sustainable solution to the problem of data updation and control of errors at the source to improve the accuracy. A sub-meter (50 cm) accuracy of GIS databbase is more than enough required for use with any OTDR and fault locator.
GIS database is an important Asset Management/Accounting tool and means of visualizing the location of the network assets quickly and presenting it in meaningful ways to assist network planning and maintenance activities. Though everyone wants highest accuracy possible but spatial accuracy of utility networks is not as important as emphasized by many GIS data users due to the following reasons:
1. GIS database cannot replace any engineering document like as-built drawing which is supposed to be the single independent document describing layout and technical characteristics of the network.
2. GIS database is best suited for tracking asset inventory, engineering analysis and customer support type activities. An updated database can be used for network planning (desired scale of 1:1000 or accuracy 1 M), fault locating, demand calculation, load change, load estimation type engineering analysis also. Again its currency and completeness are much more importnt than a pinpoint accuracy.
3. Accuracy of the top of line fault locators and OTDR available in the market are in the sub-meter range. There are no information available about their performance and accuracy and none of these claim sub-foot accuracy. So, a 50 cm accuracy map (as maintained by a carefully drawn 1: 500 scale as-built drawing) is better than what is required by any O&M staff.
4. Most of the maintenance problems and accidents during trenching occur due to human errors in cable/feeder identification, outdated as-builts and not due to its wrong location in GIS. This happens due to the use of old data/drawings that do not show current as-is situation in the ground than the issues related with the data accuracy.
Use of geophysical methods like cable tracing and Ground Penetrating Radadr (GPR) for locating underground utilities which are meant for knowing the approximate/supposed location of the objects are highly prone to errors with additional operational limitations of the equipment and ground conditions for any large project.
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