Street Light Inventory Using Digital Photography and GPS
Author: Darren Rozenek
Co-Authors: A. J. Romanelli, John Schiebold
The City of Akron Ohio was faced with the need to inventory and spatially locate its street light assets in a short amount of time. Using a combination of commercial off-the-shelf technologies the City was able to quickly and accurately complete a street light inventory of over 25,000 poles. Field data capture was facilitated by GPS and digital photo/attribute capture. Short ramp up times for field workers and high data collection rates (approximately one feature/minute) allowed the survey to be completed in three months. Office data management using ArcGIS, ArcSDE and ASP completed the data collection loop.
The City of Akron’s existing street lighting maps had become out of date and were still maintained by hand. Without an accurate inventory it became extremely difficult to track the City’s charges and operation and maintenance costs associated with the street lights. The scope of the project was to create a spatially accurate inventory of an estimated 20,000 poles and 22,000 lights in a four month time schedule. EMA Inc. was chosen by the City of Akron to help design and implement the street light inventory project. The project staff was comprised of four field workers and one GIS Editor. The inventory project can be broken into three distinct parts, the field work, the office work, and the “virtual field work”. Each part is discussed in the following sections.
The foundation of the system was the Ricoh Caplio Pro G3 digital camera. A key feature of the camera is that it allows up to five attributes to be entered in the field which are embedded in the photos at the time the picture is taken. This attribute embedding allows the field crews to record the survey information by simply taking a picture of the asset that is being inventoried. A camera and spare battery allowed for 8 to 10 hours of data collection. The spatial component was provided by a Leica System 1200 GPS receiver. Any GPS receiver that can record a track log could have been used, but the Leica units were chosen for their extreme ease of use and long battery life. The GPS receivers were carried in small backpacks and had 12 to 16 hours of battery life. Once the units were turned on in the morning, the field workers did not need to interact with the GPS receivers. Four field data collection systems were put together for the street light inventory. Each system’s components were color coded to allow for easier data organization. The color coding also helped to avoid mismatches between GPS units and cameras. As an additional quality control step, the first and last photos of each day were taken of a GPS time stamp display. These photos included a color swatch so that the image could be examined in the future if any questions arose. The time stamp photo was used during the photo linking process to provide the link between the GPS and the photos.
The survey procedure was to approach the pole to be surveyed, place the GPS receiver at the base of the pole, enter attributes using the pick lists in the camera, then step back and take a picture of the complete pole and bulb. If a pole had multiple bulbs, additional pictures were taken for each of the bulbs (different attributes were entered for each of the bulbs if needed). This process was repeated for each pole that was surveyed. When possible, cultural features such as street signs were included in the photos. This allowed for easier manual placement of the pole location during office processing if required. Each data collector had a backpack GPS unit, digital camera with a spare battery, safety vest, survey map, and an inclinometer (used for measuring pole height and arm length). Carpenter style tool pouches were used by the data collectors to carry the system components and allow for easy movement. Maps were produced of the daily work areas every morning. This allowed the GIS Editor to supply work area maps including all of the previously collected poles to minimize the possibility of duplication. Data collectors worked to completely inventory an entire map grid before moving on to the next grid. This avoided duplication of efforts and data (any accidental data duplication was caught by the loading process).
The foundation of the office work was the City’s existing ArcSDE geodatabase. All street light inventory features that had been collected where uploaded into ArcSDE. The geodatabase also contained a high resolution aerial image catalog, street centerlines and parcel addressing features, which where the main feature classes used for this project. The parcels, street centerlines and aerial imagery are all data layers built and maintained by the surrounding County Municipality ( Summit County, Ohio). ArcGIS desktop products were used to convert the existing hand drawn index maps into a feature class so that defined grids could be setup for data collection. ArcMap was also used for spatial manipulation of the collected data. ArcIMS was used in conjunction with custom ASP pages to provide an easy to use solution of providing progress to management and to complete the attribute collection. Leica’s GeoOffice Software was used to post process the collected GPS data against the City’s owned and operated base station. GeoSpatial Experts GPS Photolink software was used to link the photos to the post processed GPS data.
At the end of the day, the field workers returned to the office to turn in their equipment. Data was then downloaded from the GPS receivers and cameras to a network file store, which was backed up nightly. Batteries for the cameras and GPS units were recharged overnight. The raw data from the GPS units was differentially corrected using the City’s base station and the Leica GeoOffice software to produce a GPS track log file.
The pictures were then correlated to the differentially corrected GPS track log using GeoSpatial Experts GPS PhotoLink software. The time stamp photos were used by this software to give the time differential between the camera and the GPS units. This differential is the link that the software uses to join the photos to the GPS track log. The PhotoLink software’s output is a shapefile containing a point for each of the photos, and the attribute data extracted from the photos. In addition to the photo location shapefile, the software also output a track log shapefile that showed the location of the GPS unit throughout the day.
Once the shapefiles were generated for all four field units, the data had to be inspected. Due to GPS limitations such as poor coverage or high dilution of precision (DOP), approximately 10% of the spatial locations required manual relocation using ArcMap. The photo points were adjusted to their proper location using a combination of the photo shapefiles, track log shapefiles and the ArcSDE Geodatabase. All adjusted points then had their longitude and latitude recalculated to ensure the data was properly placed within the Geodatabase during the loading process. A single GIS Editor processed the spatial data for the four systems on a daily basis, taking on average four hours per day.
Due to the fact that some poles had two or more bulbs (which may have been different wattages or types), the pole data was maintained in an ArcSDE spatial table (layer) and the bulb data was maintained in a related non-spatial table. Once the photos were verified (and adjusted if necessary) the GIS editor loaded them into ArcSDE. A custom tool was used to load the shapefile data into ArcSDE: The tool reverse geocoded the address for each of the photos, then loaded the pole information into ArcSDE, and finally loaded the bulb information and image into the related table. The loading tool handled creation of an identifier for each of the poles and bulbs, and properly related the bulbs to the poles. Additionally, the loading tool performed quality control by preventing duplicate data from being entered into the database.
Virtual field work
A total of 12 attributes were required to be collected about each pole and lamp. Five attributes were collected during the field data collection and the remaining seven were collected by examining the digital photos in the office, which we refer to as “virtual field work”. Once the pole and luminary information was loaded into ArcSDE, a set of ASP pages allowed administrative staff (and field staff during days when data collection could not be performed) to enter additional attributes by viewing the photos. In essence, the field work was brought into the office. Attributes that were extracted in this manor included the power source (overhead or underground), the mounting type (embedded or bolted), and the style (e.g. colonial, cobra head, etc.). The virtual field work also allowed for the correction of data that had been entered incorrectly in the field. For example, if the field worker set the pole type incorrectly it could be adjusted while entering the additional attributes. An ArcIMS service was setup to supply a map viewer that allowed the entire City to track the progress of the project as well as allow the personnel that normally used the original maps the ability to submit spatial changes to the GIS Editor and use the ASP pages to make changes to incorrect attribute data.
The street light inventory project was completed in three months, one full month ahead of schedule. The final collection totals were 26,501 poles and 28,313 bulbs. This gave the City a difference of 6,501 poles and 6,313 bulbs that were not previously added into their inventory of assets. The combination of ArcGIS products and several COTS tools provided the City with the ability to quickly and accurately perform this project as well as provide an avenue for updating the system as assets are added and removed. An additional benefit of this methodology is that the digital photos of each of the poles are now available for future use by other systems. For example, a CMMS could include a picture of the pole when creating a work order for a bulb replacement. This information may also benefit the entire community such as the power company, telecommunications and cable if a cooperative effort is established.
http://www.esri.com/software/arcgis/arcsde/index.html http://www.esri.com/software/arcgis/arcims/index.html http://www.co.summit.oh.us/fiscaloffice/defaultwebapps.htm
City of Akron
146 S. High Street , Room 300
Akron , Ohio 44308
330-375-2690 ext. 6417