having trouble with the NGS tool kit to convert a NAVD88 elevation to NGVD29 datum for this point:
LAT: 42 14 28.03382 0.006(m) 42 14 28.06604 0.006(m)
E LON: 280 30 18.42760 0.006(m) 280 30 18.40122 0.006(m)
W LON: 79 29 41.57240 0.006(m) 79 29 41.59878 0.006(m)
EL HGT: 365.621(m) 0.021(m) 364.454(m) 0.021(m)
ORTHO HGT: 399.841(m) 0.024(m) [NAVD88 (Computed using GEOID12B)]
any ideas? thanks, Dan Barry
Good luck with that. I did an recent extended data GPS solution and see that Prototype GEOID16B is 0.3m different than GEOID12B.
Paul in PA
Paul, thanks for responding, trying to do a floodplain certificate, no RM's left, and VERTCON doesn't work, and cannot get the online version to work either
Here is what I usually do. I download a few NGS datasheets for points surrounding the point I want to convert, sheets which have both '88 and '29 elevations. Those differences are always the same within a hundreth or 2. Calculate an average and apply it to your point.
Mark Mayer, post: 398211, member: 424 wrote: Here is what I usually do. I download a few NGS datasheets for points surrounding the point I want to convert, sheets which have both '88 and '29 elevations. Those differences are always the same within a hundreth or 2. Calculate an average and apply it to your point.
Mark: thanks for confirming what I did after posting my request for help! Dan
I'm not sure what tool you are using. I tried VERTCON with these results. Note that a west longitude must be entered as 3 digits with leading zero as necessary.
Latitude: 42 14 28.03382
Longitude: 079 29 41.57240
NAVD 88 height: 399.841
Datum shift(NAVD 88 minus NGVD 29): -0.141 meter
Converted to NGVD 29 height: 399.982 meters
Compare the nearest NGS first order class 2 mark, 7 miles away:
NC0611* NAVD 88 ORTHO HEIGHT - 229.492 (meters) 752.93 (feet) ADJUSTED
NC0611 NGVD 29 (??/??/92) 229.678 (m) 753.54 (f) SUPERSEDED 1 2
difference -0.186 meter
NC0611 NGVD 29 (06/03/92) 229.649 (m) 753.44 (f) ADJUSTED 1 2
difference -0.157 meter
I don't understand the two old values, but VERTCON seems to be pretty close.
Thank you very much! I could not get vertcon to work for me, must be old guy error!
Paul,
Not sure what you're point is. The beta xGEOID16 model used GRAV-D data collected up to Dec of 2015 to predict what heights will be with respect to the new reference frame in 2022. It has nothing to do with either NAVD 88 or NGVD 29.
Well, with the sage advice received here, and thank you all very much, I realized my error in not placing a 0 before the longitude, now am able to use VERTCON, and the results are matching well with local benchmarks, again, thank you to all, Dan
Mr. Doyle beat me to it. Beta xGEOID16 has nothing to do with either 88 or 29.
Please don't post about GRAV-D. All we need is a 500 post thread where some surveyor from Singapore accuses us of trying to rip off the public by changing from a perfectly good datum just to generate work for surveyors.
James Fleming, post: 398297, member: 136 wrote: Please don't post about GRAV-D. All we need is a 500 post thread where some surveyor from Singapore accuses us of trying to rip off the public by changing from a perfectly good datum just to generate work for surveyors.
:p
As an aside, even if vertcon works, i still check it against local data sheets
