We are doing a research on how to visualize the varying levels of certainty of the underground utility location information. For this we had to find out what could cause an inaccurate 3D location. As a result of several meetings with the municipality of Rotterdam, we can distinguish the following situations:
- The location of the utilities is mapped using a 2D map (that does not include a z-component). In this case the depth of the cable or pipe is estimated. Since 2010 surveyors have to measure the z-coordinate of the utility (next to the x,y-coordinates)
- The location of the utilities is mapped using their relative location.
- The location of the utilities is mapped after it is burried (using GPS)
- The location of the utilities is mapped using an GPS device that comes with an inaccuracy (+/- 5 cm).
- The utilities are moving over the years (swimming pipes and cables). Most of the movement will be vertically.
- The actual ground is moving. Data has shown that the ground on the Oostplein is sinking 0 to a almost 1 cm a year. It is unsure whether the subsurface utilities are making the same movement as the above ground.
The figure above makes a comparison between two different data sets. The black line represent a profile, in which every pipe or cable is measured. The dot with number 502 is a sewage pipe. The orange line, which is the other data set, represents the exact same sewage pipe. You can see that the location is different.
The uncertain location of the underground infrastructure is a problem that people are facing all over the world. Utility companies in Manhattan mark the location of the pipes and cables on the street (see figure below).
With the information and datasets we got from the Rotterdam, we can say that the 3D location of the subsurface utilities is depending on many factors and therefore uncertain. When looking at the depth of a pipe or cable, it could be located:
- at the measured depth (unfortunately it is not measured in most cases)
- at the estimated depth
- at the standard depth (Rotterdam has their own standard)
- a few cm up/down due subsurface ground movement
- a few cm up/down due inaccurate GPS measuring