# Celestia/Celx Scripting/CELX Lua Methods/Celx vector

## Contents

# Celx Scripting: Vector[edit]

## vector[edit]

A "vector" object in Celestia is a 3-tuple of double precision floating point values, which represent a geometric object that has both a length and direction [X, Y, Z] in a 3 dimensional coordinate system.

Within a CELX script, the vector methods need to be prefixed with the obtained "vector" object, separated with a semicolon.

The following methods can be used to obtain a "vector" object:

- Using the celestia:newvector() method.
- Using the position:vectorto() method.
- Using the vector:normalize() method.
- Using the rotation:imag() method.
- Using the rotation:transform() method.
- By subtracting two "position" objects.

**Notes:**

- Vector components (X,Y,Z) in Celestia are stored in millionths of a light year. So when you have your own vectors defined in km or miles, you have to convert these vectors. Therefore, you can use a constant, which must be initialized first within your script:
- From km to millionths of a light year, use a constant uly_to_km = 9460730.4725808.
- From miles to millionths of a light year, use a constant uly_to_mls = 5912956.5453630.

- Next you can convert km or miles to millionths of a light year as follows:
- millionths_of_a_light_year =
*number:km*/ uly_to_km - millionths_of_a_light_year =
*number:miles*/ uly_to_mls

- millionths_of_a_light_year =

## Operators[edit]

"Vector" objects can be added and subtracted from each other.

It is also possible to add a "position" object with a "vector" object, or subtract a "vector" object from a "position" object.

- position + vector → position
- position - vector → position
- vector + vector → vector
- vector - vector → vector

Scalar multiplication with "Vector" objects:

- number * vector → vector
- vector * number → vector

The * operator gives the dot product of two vectors v and w:

- v * w = v.x*w.x + v.y*w.y + v.z*w.z → number

The ^ operator gives the cross product of two vectors v and w:

- v ^ w = [(v.y*w.z - v.z*w.y), (v.z*w.x - v.x*w.z), (v.x*w.y - v.y*w.x)] → vector

The new vector is perpendicular (according the right-hand rule) to the plane containing the two input vectors

- v ^ w = - w ^ v

Be careful when using this: ^ is normally the exponentiation operator in Lua, and thus has higher precedence than almost any other operator, including unary minus.

## Members[edit]

You can access and assign the x, y, and z components of a "vector" object directly, e.g.

vec = celestia:newvector(0, 0, 0) vec.x = vec.x + 1

## Methods[edit]

This chapter contains a list of all available vector methods, which can be used on "vector" objects.

### getx[edit]

number **vector:getx()**

Return the X coordinate of the vector as a number.

**Example:**

Get a vector giving the heliocentric position of the Earth and display the X-, Y- and Z-components of that vector in the lower left corner of your screen.

now = celestia:gettime() sunpos = celestia:find("Sol"):getposition(now) earthpos = celestia:find("Sol/Earth"):getposition(now) heliovector = sunpos:vectorto(earthpos) heliovector_x = heliovector:getx() heliovector_y = heliovector:gety() heliovector_z = heliovector:getz() celestia:print("Heliocentric position of Earth:\nX = " .. heliovector_x .. "\nY = " .. heliovector_y .. "\nZ = " .. heliovector_z, 10, -1, -1, 1, 6) wait(10.0)

__Return to the vector method index.__

### gety[edit]

number **vector:gety()**

Return the Y coordinate of the vector as a number.

**Example:**

Get a vector giving the heliocentric position of the Earth and display the X-, Y- and Z-components of that vector in the lower left corner of your screen.

now = celestia:gettime() sunpos = celestia:find("Sol"):getposition(now) earthpos = celestia:find("Sol/Earth"):getposition(now) heliovector = sunpos:vectorto(earthpos) heliovector_x = heliovector:getx() heliovector_y = heliovector:gety() heliovector_z = heliovector:getz() celestia:print("Heliocentric position of Earth:\nX = " .. heliovector_x .. "\nY = " .. heliovector_y .. "\nZ = " .. heliovector_z, 10, -1, -1, 1, 6) wait(10.0)

__Return to the vector method index.__

### getz[edit]

number **vector:getz()**

Return the Z coordinate of the vector as a number.

**Example:**

Get a vector giving the heliocentric position of the Earth and display the X-, Y- and Z-components of that vector in the lower left corner of your screen.

now = celestia:gettime() sunpos = celestia:find("Sol"):getposition(now) earthpos = celestia:find("Sol/Earth"):getposition(now) heliovector = sunpos:vectorto(earthpos) heliovector_x = heliovector:getx() heliovector_y = heliovector:gety() heliovector_z = heliovector:getz() celestia:print("Heliocentric position of Earth:\nX = " .. heliovector_x .. "\nY = " .. heliovector_y .. "\nZ = " .. heliovector_z, 10, -1, -1, 1, 6) wait(10.0)

__Return to the vector method index.__

### normalize[edit]

vector **vector:normalize()**

Return a normalized "vector" object.

A normalized vector is a vector that points in the same direction as the original vector, but with **length = 1**.

**Notes:**

- This method does not modify the original vector.
- Normalizing a zero-length vector causes division by zero. The result will be a vector of NaNs.
- A CELX "vector" object is a geometric object that has both a length and direction [X, Y, Z] in a 3 dimensional coordinate system.
- The vector methods can be used on a CELX "vector" object. "Vector" objects can also be used in other methods, requiring a "vector" object as an argument.

**Example:**

create a vector that points from the actual position of Earth to the actual position of the Moon, with length = 1.

earth = celestia:find("Sol/Earth") moon = celestia:find("Sol/Earth/moon") now = celestia:gettime() earthpos = earth:getposition(now) moonpos = moon:getposition(now) vector = earthpos:vectorto(moonpos) n_vector = vector:normalize()

__Return to the vector method index.__

### length[edit]

number **vector:length()**

Return the length of this vector in in millionths of a light year, as a number.

**Example:**

Display the actual distance from the __center__ of Earth to the __center__ of the Moon in km.

uly_to_km = 9460730.4725808 earth = celestia:find("Sol/Earth") moon = celestia:find("Sol/Earth/moon") now = celestia:gettime() earthpos = earth:getposition(now) moonpos = moon:getposition(now) vector = earthpos:vectorto(moonpos) distance = vector:length() * uly_to_km celestia:print("Actual distance center Earth - center Moon: " .. distance .. " km.", 10.0, -1, -1, 2, 4) wait(10.0)