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MLLW to NAVD88 elevation conversion ~ Or, How I’ve gone brain dead
I have an elevation based on MLLW in Provincetown MA. and I have blanked on the Vdatum conversion program, and can’t recall how to make the conversion. I am beginning to wonder if it’s possible without direct observation or transfer from an NABD BM….
My Benchmark is 7 1933, designation 844 61212 Tidal 7, VM 19587, the primary benchmark for that series of marks.
Thanks for any help……
Don
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8 Replies
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If there is no value for NAVD88 on the benchmark sheets like this:
you will likely have to transfer elevations or use VDatum.
I know that some of the VMs are in the NGS IDB and have PIDs associated with them, but they are not necessarily listed on the benchmark sheet.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman -
https://tidesandcurrents.noaa.gov/benchmarks.html?id=8446121
I don’t see the relationship between the tidal datum and NAVD88 or NGVD29 listed. VDATUM is your best bet short of making observations.
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FWIW, I used the site provided by SPMPLS then the VDATUM tool. Not looking close enough at the tides and currents datasheet, I entered 0.000 for the MLLW value.
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Now that I’ve taken a better look at the tidal benchmark data, is it correct to read the data summary sheet, where it states “North American Vertical Datum (NAVD88)
Benchmark Elevation Information In meters above:
7 1933 MLLW 4.218 MHW 1.285;
That the NAVD88 elevation of the BM 7 1933 is 3.2808 x 1.285 to NAVD88 MHW or (2.933 + 1.285 (meters)) x 3.2808 = 13.84′ NAVD88 elevation?
I think that’s it 🙂
Don
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Not an expert on how tides and currents folks report their data, but …
Review the previously posted images. Note that both SPMPLS?? and my computation of the difference between MLLW and NAVD88 using VDATUM agree. You correctly indicate the height of BM 7 1933 above MLLW is 4.218 meters.
Therefore shouldn??t the NAVD-compatible height (using VDATUM) be:
0 (MLLW) + 1.665 (difference between MLLW and NAVD88) + 4.218 (height above MLLW) = 5.883 meters
Converting from meters to feet [(2.54cm = one inch) *12] or (1200/3937) = 19.30 (Intl) ft or 19.30 US survey feet.
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Hi Don,
I’m pretty sure that Mass Geodetic Survey has a levelled NAVD 88 elevation listed for that benchmark.
I must have just missed you in Provincetown today
Bob
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Hi Again, Don,
I tried to copy the data sheet to you, but it looks like they have revised the web site, to keep me out, maybe.
Anyway, If you are still looking for that info, I can send over a copy in the morning.
Bob
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