Geodesy is the science of measuring and understanding the Earth's shape, size, and gravitational field.

A gravimeter is a device used to measure the Earth's gravitational field.

The geoid is the three-dimensional representation of the Earth's shape, defined by the equipotential surface of the Earth's gravity field.

An ellipsoid closely approximates the Earth's shape, with an equatorial bulge and a flattened polar region.

Geodetic latitude is measured from the equator, while geocentric latitude is measured from the center of the Earth.

Geoidal height is the vertical distance between the geoid and the ellipsoid.

Geodetic coordinate systems are commonly used in geodesy, with latitude, longitude, and height as the primary coordinates.

Surveying is the process of determining the precise location of a point on the Earth's surface.

A theodolite is commonly used to measure horizontal angles in surveying.

The axis of rotation is the imaginary line connecting the North Pole and the South Pole.

Stars are primarily used as a reference for determining latitude.

Deflection of the vertical is the difference between the geodetic latitude and the geocentric latitude.

A level is commonly used to measure vertical angles.

A meridian is the imaginary line connecting two points on the Earth's surface with the same longitude.

A total station is commonly used to measure distances.