Select all of the statements that are true:
a. datums can be established through trigonometric leveling
b. mean sea level corresponds to our current vertical datum
c. dynamic heights are the same as orthometric heights
d. geoid models have improved through time
e. ngvd29 was matched to more tidal stations than navd88
f. all leveling surveys use levels

a. Datums can be established through trigonometric leveling.

d. Geoid models have improved through time.

e. NGVD29 was matched to more tidal stations than NAVD88

Explanation:

a. Datums can be established leveling with trigonometric form, is a method to determinate different elevations.

d. Geoid models have been improved through time in the gravimetric geoid model and increase accuracy, actually, these models keep refining, there were errors ins this models, nowadays are more accurate.

e. NGVD29 was matched by tidal stations more than NAVD88.

NGVD29 was established by 26 tidal gauges in United Stated and Canada, maps were prepared, but NGVD29 was replaced because is less accurate than NAVD88.

NAVD88 were not used Additional tidal.

False sentence

b. The average sea level doesn't correspond to our current vertical data, this depends on our location.

For example

Rinconada in Peru is the highest human establishment in the world to 5100 m.

Everest is the highest summit in the world to 8848 m.

This marker indicating the sea level is located in Jerusalem.

c. Often is used levels, but there are other methods like set-up, bench mark.

f. the Dynamic heights are not the same as orthometric heights, because the dynamic heights are perfect, but the orthometric heights can change slightly, in a few words are imperfect heights.

1. a

2. a

3. d

explanation: