GIS Inspection using GPS and Digital Camera

Goal
The goal of this paper is to share the methodology and experience CADDScan developed for a utility inspection project. Due to traffic and manhole water constraints, an automated underground manhole inspection approach was developed to quickly collect and record the field data. The inspection process utilized a Trimble GPS system, Trimble Data Dictionary, Digital Camera, Differential Correction, MicroStation CADD program, Micro Station Development Language (MDL), ESRI Arc/Info, and ESRI MapObjects development tools.

Introduction
CADDScan was a contractor to Bell Atlantic Network Integration (BANI), providing utility inspection and verification services for the City of Baltimore’s 800Mhz Radio Implementation Project. One of CADDScan’s primary responsibilities was to identify existing conduit holes available for the fiber optic cable connectivity. There are approximately 800 manholes within the project area. Each manhole must be quickly surveyed and inspected - because many of them reside in high traffic density area and are water filled. In order to minimize the time required to locate the manhole coordinates and collect the necessary project data, Trimble GPS with pre-defined input interface was developed for convenient field data input. At the beginning of the project, a camcorder was used to record the condition inside the manhole. Later into the project, the project team discovered that it was rather difficult to identify where in a tape the information for a specific manhole is located. A Kodak digital camera was then selected to replace the camcorder and was found to be time-efficient and easy to use.

After the fieldwork was completed, the GPS field data was downloaded to an office computer for further processing. The Trimble Pathfinder program was used to perform coordinate projection, GPS post differential correction, and data export to Arc/Info file format. The Arc/Info file was also converted to Micro Station format with attribute pointer reserved as a part of the Micro Station element data. The reason for this conversion was to enable database attribute review and verification, while creating design drawings within Micro Station environment. The Arc/Info to MicroStation conversion can be accomplished using an AML program from the Arc/Info environment. CADDScan also has a utility to read Trimble-generated MicroStation files, reserving database linkages.

A user interface was developed using MicroStation Development Language (MDL), which enables attribute accessing from within MicroStation. The photo image names were entered as attributes in a separated database table pointing back with the corresponding manhole. Users can click on a manhole to display the photo images to verify the selection of the conduit slots is acceptable.

Since Arc/Info was the required GIS deliverable format, CADDScan also developed an ESRI MapObjects-based graphic user interface to allow the project staff to access the manhole data directly from a Microsofl Windows environment.

The manhole inspection work was completed in approximately three months. GPS utilization significantly reduced the required time for locating manhole coordinates. Without using the camcorder and the digital camera, it would have been impossible to go back to the water filled manhole for design verification. MicroStation successfully produced the construction drawings and the as-built documentation. Manhole GIS data sets are maintained as a reference for future overlays in Arc/Info format. Since a digital camera was not used until later in the project, most of the manhole photos were taken by a camcorder. At this time, the project team does not maintain a complete photo set for all the manholes that were inspected.