Watch the overview
About 2 minutes. A narrated explainer; the same words are below.
Read the video text
- 0:00Every reading on a road survey is pinned to a spot on the road.
- 0:04If that spot is not on the road, the reading has nowhere to live.
- 0:11Think of the road as a ruler with two ends.
- 0:14Every reading must sit between those ends. Anything off the ruler is out of place.
- 0:19In TMH 18, version four, the network file is the reference for all other data.
- 0:26It lists each road, its start and end kilometre, and its valid dates.
- 0:33The standard says the start and end kilometre of your data must fall within the road's range.
- 0:39Values outside it will be discarded, checked against the current road version.
- 0:46Each record names its road, and gives a start kilometre measured on that road's network record.
- 0:52Lane data needs a lane code, and every record a survey date.
- 0:58When a road's alignment changes, the network file is sent again, and that makes a new version of the road.
- 1:05Data maps to the version by survey date. A new network file with conflicting dates is not loaded.
- 1:13Before you upload, open the network file. Copy each Road ID exactly, and take every kilometre from that road's own record.
- 1:22Then check no reading falls before the start or past the end.
- 1:29Picture a road that ends at one kilometre mark, and a reading logged beyond it.
- 1:34That reading is outside the road's range, and the standard says it will be discarded.
- 1:40In TMH18 Validator, you choose the check template yourself when you upload.
- 1:45Do not assume the checks compare every kilometre with the network file. A clean run is not proof that it fits, so compare them yourself.
- 1:54The standard also disagrees with itself on Road ID and lane code lengths, and on the kilometre format.
- 2:01The text does not reconcile them, so ask the receiving authority which limit it applies.
- 2:08So: the network file sets the kilometres. Keep every record inside them, and compare them yourself before you upload.
- 2:16The full guide is at TMH18 dot com, slash articles.
What does the TMH 18 network file set?
In TMH 18, version 4 (headed 'Draft Version 4', October 2014), the network definition file is the base for all other data. It has the extension .net. It holds each road, its start and end km (the km position along the road, often called chainage), and the dates for which that description is valid. For the whole flow from file to certificate, read TMH 18 data validation.
Other files are tied back to it. A road classification file may only use Road IDs that exist in the network file (section 3.1). Every network record also needs a matching entry in the geometry file (section 2.3).
Network files carry dates. When a road's alignment changes, the standard says the network file is sent again, and that creates a new version of the road (section 2.2.2). If a new file's date range conflicts with the network already loaded, the standard says it is not loaded and an error is returned (section 2.2).
Which fields tie a record to the network?
Table 6 lists the base fields for every data file. Road Id is required and is a key into the network table. Lane Code is required whenever the data describe one lane. The survey date is required. Start KM is required and must refer to the km position as measured on the network record for that Road Id.
One convention sits behind the km values. The primary direction is the side where km increase toward north or east, and it applies to the whole route (section 4.1). Lane codes are a separate subject, covered in the RoadSense guide on map, lane and wheelpath conventions across manuals.
- Use each Road Id exactly as it appears in the network file.
- Take Start KM from the km base on the network record.
- Give lane-specific data a Lane Code.
- Include the survey date; the standard maps data to the road version by that date (section 2.2.2).
What happens to data outside the km range?
Section 5 says the start and end km of the data values must fall within the start and end km of the road in the network definition file. It adds that values outside that range will be discarded. Section 2.2.2 says validation checks are performed so that data is not submitted outside the current road version's minimum and maximum km range.
Read these as rules for the system that receives the data. The standard describes what that system does. It does not say TMH18 Validator does any of it. For you, the lesson is practical: a reading at 14.100 km on a road that ends at 12.500 km is outside the base, and the standard says it can be lost.
Where does the standard disagree with itself?
Version four is not consistent in places that touch km and Road IDs. Road Id is a maximum of 20 characters in Table 6 and 12 characters in the network definition table. Lane Code is 5 characters in Table 6 and 4 in a visual condition table.
Start KM is Decimal(6,3) in Table 6, while Table 3 shows a typical km field as Decimal(5,3). Most km fields are formatted 999.999, but the flexible pavement visual condition table says 999.99. The standard does not say which value wins, so ask the receiving authority which limit it applies.
What does TMH18 Validator confirm?
When you upload a file, you choose a Check template. The template sets the checks that run. Results appear as findings, shown as Error or Warning, and a run also counts Passed and Skipped checks. A result describes the checks that ran, nothing more.
We have not confirmed that any check compares a record's km with the network file. Do not treat a clean run as proof that your km values sit inside the road. Compare them with the network file yourself before you upload, and browse the Check templates to see what each one covers.
Put it into practice
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