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Specifications and Classification Standards – There is a Difference

Photo of TBM - Tunnel Surveying Requires the Ultimate in Accuracy Specifications
Tunnel Surveying Requires the Ultimate in Accuracy

I was nervous yesterday about my webinar presentation on 3D survey accuracy and positional uncertainty specifications and standards. It’s a complicated subject and I knew there would be a number of smarter and more experienced people than me in the audience.

Overall things went well, but I did hear from the most experienced and knowledgeable heavy construction, control surveyor that I know. (Tunnels – see above being the toughest control survey challenge of them all.) He passed along a paper by Dennis G. Milbert at the NGS from 1983 entitled, “A Specification is Not a Classification Standard.” One may think that the differences are subtle, but as the author points out that is not the case. So I will be more careful about interchanging those terms in the future.

Here are some excerpts from the paper.

“A sharp distinction is drawn between a classification standard and a specification. Briefly, a classification standard is a more or less an arbitrary rule used to classify geodetic control. A specification, on the other hand, is a rule derived from experience of how to achieve the classification standard. (For instance, an example of the latter might be the Caltrans Survey Manual.)

Consideration is turned to the equally sharp difference between precision and accuracy. It is shown that specifications typically control precision, whereas the classification standard is based on accuracy. With a clear understanding of the differences between standards and specifications, we become better equipped to develop specifications that more effectively support the standards of classification.”

Well said and it makes perfect sense when you think about it for awhile. It helps one to organize their thinking on this important subject. Terminology matters.


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