It only affects Puerto Rico and the USVI.
Yes, that is correct. However, if you pull a datasheet for a point in your state and look at the orthometric height, it will state it was derived using GEOID12B. In California, the Public Resources Code states that we are to use the latest geoid model to derive NAVD88 heights, therefore, we are to use 12B, even though it is exactly the same as 12A here.
Geoid12B is out...
...how far out?
Perhaps, but I should elaborate:
My OPUS solution processed this morning for a 4+ hour file collected last week from Central Texas, has GEOID12B stated on the output.
SOFTWARE: page5 1209.04 master90.pl 022814 START: 2015/04/23 14:54:00
EPHEMERIS: igr18414.eph [rapid] STOP: 2015/04/23 19:26:00
NAV FILE: brdc1130.15n OBS USED: 12716 / 13357 : 95%
ANT NAME: TRMR8_GNSS NONE # FIXED AMB: 75 / 79 : 95%
ARP HEIGHT: 1.756 OVERALL RMS: 0.020(m)
REF FRAME: NAD_83(2011)(EPOCH:2010.0000) IGS08 (EPOCH:2015.3088)
X: -782673.712(m) 0.009(m) -782674.498(m) 0.009(m)
Y: -5455705.560(m) 0.016(m) -5455704.103(m) 0.016(m)
Z: 3199675.620(m) 0.005(m) 3199675.438(m) 0.005(m)
LAT: 30 18 15.14334 0.006(m) 30 18 15.16004 0.006(m)
E LON: 261 50 9.84754 0.007(m) 261 50 9.81068 0.007(m)
W LON: 98 9 50.15246 0.007(m) 98 9 50.18932 0.007(m)
EL HGT: 281.359(m) 0.016(m) 280.118(m) 0.016(m)
ORTHO HGT: 306.005(m) 0.030(m) [NAVD88 (Computed using GEOID12B)]
UTM COORDINATES STATE PLANE COORDINATES
UTM (Zone 14) SPC (4204 TXSC)
Northing (Y) [meters] 3352790.653 4274138.152
Easting (X) [meters] 580391.232 680421.796
Convergence [degrees] 0.42189544 0.40960064
Point Scale 0.99967973 1.00000610
Combined Factor 0.99963556 0.99996192
US NATIONAL GRID DESIGNATOR: 14RNU8039152790(NAD 83)
BASE STATIONS USED
PID DESIGNATION LATITUDE LONGITUDE DISTANCE(m)
DF4373 TXAU AUSTIN RRP2 CORS ARP N301842.088 W0974522.712 39218.2
DG5765 TXJC JOHNSON CITY CORS ARP N301559.203 W0982350.395 22843.3
DN6089 SAM2 SAM AUSTIN CORS ARP N301420.448 W0975011.323 32327.8
NEAREST NGS PUBLISHED CONTROL POINT
BN0612 SHINGLE HILL N301814.171 W0980547.053 6490.0
This position and the above vector components were computed without any knowledge by the National Geodetic Survey regarding the equipment or field operating procedures used.
> Perhaps, but I should elaborate:
> My OPUS solution processed this morning for a 4+ hour file collected last week from Central Texas, has GEOID12B stated on the output.
I noticed this on my OPUS solution from an observation taken on Wednesday last week. High geomagnetic activity though, so I'm going to have to run it again. Interesting to see though.
> Yes, that is correct. However, if you pull a datasheet for a point in your state and look at the orthometric height, it will state it was derived using GEOID12B. In California, the Public Resources Code states that we are to use the latest geoid model to derive NAVD88 heights, therefore, we are to use 12B, even though it is exactly the same as 12A here.
Just curious what your thoughts are, but the California PRC also allows for the use of CSRC published coordinates. Being that the current CSRC control is on NAD83(2007), doesn't this mean you are allowed to use NSRS2007, but you must erroneously apply Geoid12B?
In California, the Public Resources Code states that we are to use the latest geoid model to derive NAVD88
Really? Does that mean that you have to apply some OPUS/GEOID12B to get the elevations; even if they are quite different from published NAVD88 bench marks?
> In California, the Public Resources Code states that we are to use the latest geoid model to derive NAVD88
>
> Really? Does that mean that you have to apply some OPUS/GEOID12B to get the elevations; even if they are quite different from published NAVD88 bench marks?
It is not a requirement. The code is as follows:
"8895. Geoid Models
When a geoid model is used to determine COH88 values, it shall be the latest geoid model published by NGS.
My original statement was mis-leading. Dan - thank you for posting the actual code language for clarification.
However, the PRC needs a lot of work in these sections and a team is being assembled to undertake that work. It does say "when a geoid model is used", not "a geoid model must be used." By no means could that language be interpreted to mean that leveled NAVD88 bench marks cannot be used to establish COH88 values. However, there are areas in California that are currently subsiding at a rate of a foot/year, possibly more with the drought. If one grabs an elevation as gospel, because it is an NAVD88 leveled BM and does a Flood Elevation Certificate (or any elevation critical work) without using OPUS (or something) as a check when working in or near these areas, well, good luck with that.
However, when establishing COH88 elevations using a geoid model, it is a requirement that the latest NGS geoid model shall be used. This needs to be fixed to allow for the "appropriate" geoid model to be used, as in the situation Dan referred to (earlier realization of NAD83). Section 8896 does allow for making "local orthometric height corrections" to the published geoid model, such as adding leveled marks that were not included by NGS in the creation of the latest geoid model.
However, there are areas in California that are currently subsiding at a rate of a foot/year, possibly more with the drought. If one grabs an elevation as gospel, because it is an NAVD88 leveled BM and does a Flood Elevation Certificate (or any elevation critical work) without using OPUS (or something) as a check when working in or near these areas,
I get you, but if the area is subsiding and the flood plain was developed using the bench marks in the area, wouldn't flood plain sink with the bench marks?
No doubt it's waaay more complicated than that, but I still would be nervous about applying the OPUS Geoid number over a more local monument.
But then most of my CORS stations are over 100 miles away;-)
