Abstract
The core principles of collecting good quality data from site for creating CCTV inspection reports including some explanations of how to avoid common mistakes.
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The PLR Naming Convention
Most global drainage inspection standards include a system for naming pipes based on either the upstream manhole ID or a combination of both the upstream and downstream manhole IDs. The Manual of Sewer Condition Classification (MSCC) defines the naming convention for WRc pipe and sewer inspection using the Pipe Length Reference (PLR) system at all times:
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Then, we use Y (maybe Z as well) to name the other outgoing pipes as MH1Y and MH1Z (remember. the PLR only considers the upstream node and the PLR Suffix). There are of course now 2 pipes going from MH1 to CP1 and a 3rd pipe going from MH1 to somewhere else. This is why we need to be able to accurately and uniquely define the ID of each pipe in the ground. One pipe, one ID.
There is no hard and fast prescribed way of deciding how to use which PLR Suffix for each pipe except that the X pipe should always be the primary outgoing pipe. After this, you can select to name the PLR Suffix for the other outgoing pipes by:
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This is great idea which includes built in resiliency into the drainage network and usually works well, except that during normal operational conditions, we are only alerted to a problem when all three pipes are blocked or failed, so the remedial works will be much more significant than if there is only 1 outgoing pipe.
HADDMS Pipe Referencing
The HADDMS inspection standard follows the same PLR Suffix naming convention of Upstream Node plus PLR Suffix, except that it does not X, Y and Z for the PLR Suffix. Instead, it uses a dot and a numeric incremental counter like .1, .2, .3 etc so the MH1X pipe in the diagram above would be MH1.1, MH1Y is MH1.2 and MH1Z is MH1.3.
The HADDMS data format system does not consider the WRc xml file data and specifies its own limits for the number of characters allowed on nodes and pipe IDs, so the use of 2 characters here is of no consequence in this data system.
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As an overall summary concept, we find that when you ask CCTV surveyors to put together a site drainage sketch, they very quickly draw the outline of the building and mark up some manhole and other point assets and usually think of major assets in numeric terms, so MH1, MH2, MH3 etc. But, they pay less attention to more minor assets and this is where the problems begin. Remember - each node ID (major or minor) must be unique on the site, and every pipe ID must also be unique. One point asset on the ground, one node ID. One linear asset below the ground, one pipe ID. |
HADDMS Pipe Referencing
The HADDMS inspection standard follows the same PLR Suffix naming convention of Upstream Node plus PLR Suffix, except that it does not X, Y and Z for the PLR Suffix. Instead, it uses a dot and a numeric incremental counter like .1, .2, .3 etc so the MH1X pipe in the diagram above would be MH1.1, MH1Y is MH1.2 and MH1Z is MH1.3.
The HADDMS data format system does not consider the WRc xml file data and specifies its own limits for the number of characters allowed on nodes and pipe IDs, so the use of 2 characters here is of no consequence in this data system.
Other than that, the logic is exactly as described here.
Infonet Data
The Infonet data management system from Innovyze is commonly used across a number of water companies and users of this data often see a column in asset lists for CCTV and cleaning called ‘Link Suffix’ which usually has a numeric value. If you see a spreadsheet with 1,000 lines of pipes, then the must common link suffix (maybe ¾ of the lines) will be 1, them a smaller number of 2s and an even smaller number of 3s. It is even possible to see numbers going up as high as 8 or 9.
It is mistake to assume that the Link Suffix is the same think as the PLR Suffix in WRc data where 1 = X, 2 = Y, 3 = Z etc. This is not the case.
Infonet contains a useful logic where inlets and outlets (i.e. not just outlets) at a manhole are numbered and when we do not know where they go or what the node is at the other end of the pipe, then their GIS system will create a nominal 1m long stub pipe at the clock position defined by the user, so at least there is an indication that there is a pipe here but we don’t know where it goes or where it comes from.
This works well in Infonet and helps with connectivity analysis, but there is no concept of this in the WRc MSCC data stream which is why using this value to create PLRs is not recommended.
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Good Site Drawings
Everything described above regarding avoiding problems with data in software applications can be avoided by taking care and time to create good quality site drawings. The process described here considers a domestic CCTV inspection but the recommended logical approach can be extended to any type of CCTV inspection.
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That’s it, your job as a CCTV surveyor is complete provided that the video files and data that you have recorded on your CCTV camera match up with this drawing. Based on the information reported here, the office rehab manager can either go with your recommendations or create their own, but regardless of which way they go, they have enough information in the video files, pictures and (most importantly) the very good site sketch to make all the good and proper quotations needed for this job.
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Understanding STC25 Manhole References
It is common when working with water company asset records to see STC25 manhole references like NZ24567401 (made up example) and although this seems like a mad set of numbers and letters, the way these are constructed is actually quite simple and is described in Appendix A of the MSCC.
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To understand the STC25 reference, we must split it up into its 5 constituent parts:
NZ 24 56 7 4 01
NZ = the 100km grid tile that you are currently in as described and specified by the Ordnance Survey. Remember 100km = 100,000 metres.
24 = the 24th kilometre across the NZ box from the bottom left corner starting at 00.
56 = the 58th kilometre up the NZ box from the bottom left corner starting at 00.
7 = the 7th 100m segment across the km grid square starting at 00.
4 = the 4th 100m segment ip the km grid square starting at 00.
01 = numeric counter as described previously.
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OS grid tiles.
From this, we can deduce that the NZ 100km grid tile is in the North West of England, and if we count 24Km East from the bottom-left corner of the tile and 56Km North from the bottom-left corner of the tile, then we hit the red cross:
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