Watch the overview
About 3 minutes. A narrated explainer; the same words are below.
Read the video text
- 0:00Someone hands you road survey data with a certificate attached. What does that certificate promise?
- 0:07Less than many people assume, and more than nothing.
- 0:12In everyday words, it is a signed receipt for one particular file.
- 0:16It records that the file was checked, reviewed, and approved.
- 0:22TMH 18, version four, defines file formats only. It sets no certification, sign-off or fingerprint rules.
- 0:31So the certificate belongs to TMH18 Validator, not the standard. It is not equipment certification either.
- 0:41A co-signer approves the file, then a final certifier issues the certificate.
- 0:47The certifier must be neither uploader nor co-signer. Errors without a recorded exception block certification; warnings never do.
- 0:57The system stores a SHA-256 fingerprint, worked out from the bytes of the file.
- 1:05Change one byte and the fingerprint changes. The certificate belongs to one exact file.
- 1:12To check one, open the public verifier and enter the certificate ID. No sign-in is needed.
- 1:20For an active certificate, it shows who signed, co-signed and certified, the issue date, and the SHA-256.
- 1:30The verifier does not look inside your file. Work out the SHA-256 of your copy, and compare.
- 1:38If the values differ, you hold a different file, and this certificate does not cover it.
- 1:44Say a contractor sends you a roughness file and a certificate, and the fingerprints match.
- 1:49So this is the file the reviewers certified. It does not tell you the measurements are right.
- 1:55A certificate does not prove the measurements are right. The checks and the review do not re-measure the road.
- 2:01A skipped check is not a pass, and a permitted user can record an exception with a written reason.
- 2:07So ask which template was used, and read every exception.
- 2:13Someone allowed to certify can withdraw a certificate; the verifier shows the reason publicly.
- 2:19It then reads Withdrawn and tells you to treat the dataset as untrustworthy.
- 2:26A certificate records who decided, and which file. It is evidence of a process, not proof of measurement.
- 2:34Look it up, compare the fingerprint, and ask what was checked.
- 2:38The full guide is at TMH18 dot com, slash articles.
What is a TMH18 Validator certificate?
If you receive survey data with a TMH18 Validator certificate, you hold a record of a review decision. People reviewed the checked file, a co-signer and a final certifier recorded their approval, and the system issued a certificate for that one file.
It is not equipment certification. It says nothing about whether a scanner or profiler was calibrated. TMH 18, version 4 (headed 'Draft Version 4', October 2014), defines file formats only. It sets no certification, sign-off or hash rules, so the certificate is a feature of TMH18 Validator, not of the standard.
What does the SHA-256 fingerprint tie to?
When the certifier issues the certificate, the system stores a SHA-256 value, a short fingerprint worked out from the bytes of the stored file. Change one byte and the fingerprint changes. The certificate is therefore tied to one exact file, not to a project or a road in general.
Certified files are also locked in the system, so the stored copy cannot be edited afterwards. The fingerprint lets you ask whether the file you hold is the file that was certified.
What does a certificate not prove?
A certificate does not prove the measurements are right. The checks look at the file against the selected check template. A person reviewed the results. Neither step re-measures the road.
Skipped checks are not passes. The certificate also does not mean the file is free of findings. A reviewer with the right privilege can record an exception, with a written reason, against most errors and warnings. A few processing notes, such as a comma-delimiter reprocess, cannot take one. Errors that remain without an exception block certification, and warnings never do.
So treat the certificate as evidence of a process. Ask your contractor which checks ran, and read any recorded exceptions before relying on the data.
- Ask which check template was used.
- Ask for the findings and any exception reasons.
- Ask how the survey itself was calibrated and controlled.
How do you verify a certificate?
Open the public verifier at Verify a certificate and enter the Certificate ID. You do not need to sign in. If the record is active, it shows who signed, co-signed and certified it, when it was issued, and the SHA-256 value.
The verifier does not check the contents of a separate file on your device. Compare the fingerprint yourself: work out the SHA-256 of the file you were given and match it with the value shown. A different value means a different file, and it needs its own review.
What does a withdrawn certificate mean?
A certifier can withdraw a certificate. They must give a reason of at least five characters, and the verifier shows that reason publicly. The certificate then reads Withdrawn, and the SHA-256 row is no longer shown.
The file itself stays in the Certified status. Withdrawn is not the same as Rejected. If you see a withdrawn certificate, do not rely on the dataset until the reason is explained and the data is reviewed again.