# n-vector

Normal vector and distance for a sphere

``npm install n-vector``

# n-vector

Stability: 1 - Experimental

Normal vector and a distance function to determine central angle between normal vectors.

## Installation

``````npm install n-vector
``````

## Tests

``````npm test
``````

### Visual test

``````npm run sketch
``````

## Usage

``````var NVector = require('n-vector');

var position1 = NVector.fromLatLon(31.565665, -96.811523);
var position2 = NVector.fromLatLon(31.465952, -97.026443);
var centralAngle = NVector.distance(position1, position2);
// 0.0036406600953623955
var greatCircleDistanceInKm = centralAngle * 6371; // Earth radius ~6371km
// 23.194645467553823 km
var greatCircleDistanceInMi = centralAngle * 3959; // Earth radius ~3959mi
// 14.413373317539724 mi
``````

## Overview

The normal vector to the Earth ellipsoid (called n-vector) is a non-singular position representation that turns out to be very convenient for practical position calculations.

source: A Non-singular Horizontal Position Representation

The non-singular aspect of n-vector makes the calculations required simple and without special cases to consider that are present when dealing with crossing prime meridian and at the Earth poles. For a deeper and more precise explanation see A Non-singular Horizontal Position Representation.

## Documentation

### NVector

Public API

• `DEGREES_TO_RADIANS`: Number 0.0174532925, multiplier to convert decimal degrees into radians.

#### NVector.distance(a, b)

• `a`: NVector First normal vector.
• `b`: NVector Second normal vector.
• Return: Number Central angle between `a` and `b` (multiply by sphere radius to determine the great circle distance).

Returns a central angle between two instances of `NVector`. To get actual distance, multiply the central angle by the estimate of Earth's radius (if it was a perfect sphere), 6371km or 3959mi.

#### NVector.fromLatLon(latitude, longitude)

• `latitude`: Number Latitude in decimal degrees (ex: 31.565665).
• `longitude`: Number Longitude in decimal degrees (ex: -96.811523).
• Return: NVector Normal vector corresponding to given latitude and longitude.

Creates a new `NVector` instance from given latitude and longitude.

#### new NVector(x, y, z)

• `x`: Number NVector "x" component.
• `y`: Number NVector "y" component.
• `z`: Number NVector "z" component.
• Return: NVector Normal vector with `x`, `y`, and `z` components.

Creates a new `NVector` instance.

## Sources

The implementation has been sourced from:

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