However the original NAVD88 data base received from the National Geodetic Survey says "modeled", because where a benchmark exist and gravity value is not available its magnitude was interpolated from a grid.
One of the basic quantities needed to compute the orthometric height, the geopotential number, is taken directly from the results of the general adjustment NAVD88.
The difference between Helmert's orthometric height and the rigorous orthometric height can be large enough to overpass the expectancies of accuracy of the NAVD88 network.
Gravity values and leveling from field work can be associated with standard deviations by INEGI itself, but here can be noticed the lack of deviations from the NAVD88 network (geopotential numbers and estimated heights don't show specific standard deviations for BN10709).
Se tuvo especial cuidado en que todos los bancos de nivel estuvieran ajustados al NAVD88
Since the complete tidal correction has been applied into the definition of the NAVD88 [Balazs and Young, 1982] and also Adj.
The residuals of height anomalies [DELTA][zeta]([OMEGA]) on the GPS/leveling points, where Helmert's orthometric heights are available in the vertical datum NAVD88 [Mainville, 1997], are computed according to the following equation
As follows from the results of the numerical investigation summarized in Tables 1 and 2, the telluroid computed from the orthometric heights in the vertical datum NAVD88 approximates the EGM96 telluroid better than the telluroid computed based on the orthometric heights in the vertical datum Adj.
Los levantamientos 9eodesicos verticales comprenderan todas aquellas operaciones de campo dirigidas a determinar la distancia vertical que existe entre puntos situados sobre o cerca de la superficie terrestre y el nivel de referencia definido por el NAVD88
and NAD83 coordinates shall be provided for all fittings and valves 2.