PLS30820, post: 327444, member: 1439 wrote: Yeah, us too on the East Coast. The question is not about NGVD29 or NAVD88... You made that clear in your first post
I, and I think all the subsequent posters assumed the OP intended to reference NGVD29, unless there is some magical NAVD29 datum I have never heard of.
PLS30820, post: 327442, member: 1439 wrote: look at the first post. [hl]READ it[/hl]. he says "NAVD29", NOT "NGVD29"
We all noticed that. It was pounced on pretty quick. We moved on...
sorry........
yyamahayzf, post: 327383, member: 1469 wrote: I am currently using Trimble Access, does anyone know if I can use NAVD29. If so where can I find the add-on. TIAA
The only way I know of is to make access "think" you are on NAVD88, occupy the NGVD29 bench mark and apply the geoid model to it.
Let the ellipsoid height go wherever it will.
I have no idea what to do if all you have is a network rover. Calibrating elevation control is always iffy
Practically every "benchmark" we commonly use for every day work is a 29 model. Everything from bridges to old highway benchmarks to known reference monuments for flood elevations in many small towns to manhole lids and gutter inlets. Add about 0.45 feet everywhere and you'll have an 88 value, or danged close to it.
I think the size of the project and accuracy requirements could dictate what you are doing as well on a few acre site I think a simple conversion could be applied. On a long project the only thing to do would be to run level loops and calibrate or trust the control and calibrate the network rover should handle it, you could cross check this with verticon. The first of the 2 options is much safer in my opinion. In se Wisconsin there is a huge amount of 29 control(every section corner). I will also say the difference between 29 and 88 here is a few tenths or less.
I've always used corpscon, it not only converts horizontal but vertical datums also
billvhill, post: 327573, member: 8398 wrote: I've always used corpscon, it not only converts horizontal but vertical datums also
Be careful, CORPSCON has known "bugs".
Incorrect scale factors being one of them.
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Kevin Samuel, post: 327577, member: 96 wrote: Be careful, CORPSCON has known "bugs".
Incorrect scale factors being one of them.
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Thanks for the info
Holy Cow, post: 327535, member: 50 wrote: ... Add about 0.45 feet everywhere and you'll have an 88 value, or danged close to it.
Perhaps everywhere in Kansas. In Portland the difference is about 3.3 feet.
Uh, yeah. That's what I meant. Everywhere "I" go.
Your differential may vary.
In a thread a few months ago we seemed to find that the Corpscon bug was that the combined scale factor was correct if and only if the output elevation was chosen as NAVD88.
https://surveyorconnect.com/threads/corpscon-6-combined-scale-factor-wrong.309050/
If that's the case, it should be a relatively simple fix for them to make in the software, but apparently they have abandoned it.
Holy Cow, post: 327535, member: 50 wrote: Practically every "benchmark" we commonly use for every day work is a 29 model. Everything from bridges to old highway benchmarks to known reference monuments for flood elevations in many small towns to manhole lids and gutter inlets. Add about 0.45 feet everywhere and you'll have an 88 value, or danged close to it.
That is an interesting number, it's really close to 2.45 here, and now I see that the new adjustment will subtract just over 2' from NAVD88 to get the whatever it will be called new elevations. Almost NGVD29 again.
Mark Mayer, post: 327583, member: 424 wrote: Perhaps everywhere in Kansas. In Portland the difference is about 3.3 feet.
F.Y.I.
A blanket conversion factor of 3.42' for Corvallis, according to the planning dept. 😉
VDATUM available free from NGS will convert between different vertical datums. Tying to monuments with 29 values is better, but VDATUM is better than nothing.
VERTCON is the magic engine within CORPSCON. Cape Cod: NGVD - 0.9 = NAVD per VERTCON. NGVD - 1.3' = NAVD based on field.
Subsidence rates vary from 1 to 3 mm/year here, so every year some BMs are losing 0.01'. The most recent NGS run was in the mid 90's, so we can see 0.20' vertical difference with long observation CORS.
