Surveying Glossary — Letter N

NAD83 (North American Datum of 1983) is the primary geodetic reference system used for mapping and surveying in North America, defining the precise coordinate framework for all spatial data.

Nadir aerial imagery is vertical aerial photography captured directly downward from an aircraft or drone, perpendicular to the Earth's surface, used in surveying for orthophoto generation and spatial analysis.

The nadir point is the location on Earth's surface directly below a satellite, aircraft, or survey instrument, representing the perpendicular intersection with the ground plane.

A standardized system of geographic reference coordinates used by surveying and mapping authorities to establish precise positions across a nation's territory.

Normal Distribution Transform (NDT) is a probabilistic point cloud registration algorithm used in surveying and mapping to align 3D laser scan data with high precision and speed.

NDVI is a standardized mathematical index calculated from multispectral satellite or aerial imagery to quantify vegetation health and density across surveyed landscapes.

Network adjustment is the mathematical process of distributing measurement errors across surveying observations to achieve the most probable positions of surveyed points in a network.

The NSRS is the official framework of geographic coordinates and elevations maintained by NOAA that provides the authoritative reference system for all surveying, mapping, and positioning activities in the United States.

NTRIP (Networked Transport of RTCM via Internet Protocol) is an open-source protocol for streaming real-time GNSS correction data over the internet to enable centimeter-level positioning accuracy.