I have a spec that calls for U.S.C. & G.S. datum. What is the relationship between that & NGVD 29?
Thanks,
SS
I cannot remember where I have ran into this, but I believe USC&GS Datum is synonymous with NAD27 horizontal datum. How it relates to NGVD29, I don't know.
The actual definition would depend on the year the height was determined. In general whenever anyone references the "USC&GS" or even the "USGS" datum they are referring to NGVD 29 for the vertical and NAD 27 for the horizontal. During my time at NGS I found that the reason these designations were given is because that's what's inscribe on the disk that they used. The USC&GS published heights in four different adjustments prior to NGVD 29 (1899,1903,1907 & 1912) commonly referenced as the First, Second, Third and Fourth General Adjustments, which is why it's important to know the date.