Class: OpenC3::Quaternion

Inherits:
Object show all
Defined in:
lib/openc3/utilities/quaternion.rb

Overview

A quaternion where q is the scalar component

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(array = [0.0, 0.0, 0.0, 0.0], angle = nil) ⇒ Quaternion

Create a Quaternion given the initial components

the forth value is the scalar or [Array<Float, Float, Float>] which as an axis of rotation



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# File 'lib/openc3/utilities/quaternion.rb', line 36

def initialize(array = [0.0, 0.0, 0.0, 0.0], angle = nil)
  if array.length == 4
    @data = array.clone
  elsif array.length == 3 and angle
    a = 0.5 * angle
    s = sin(a) / sqrt((array[0] * array[0]) + (array[1] * array[1]) + (array[2] * array[2]))
    @data = []
    @data[0] = array[0] * s
    @data[1] = array[1] * s
    @data[2] = array[2] * s
    @data[3] = cos(a)
  else
    raise "Invalid arguments given to Quaternion.new"
  end
end

Instance Attribute Details

#data ⇒ Array<Float, Float, Float, Float>

the last element is the scalar



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# File 'lib/openc3/utilities/quaternion.rb', line 72

def data
  @data
end

Class Method Details

.arc(f, t) ⇒ Object 



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# File 'lib/openc3/utilities/quaternion.rb', line 164

def self.arc(f, t)
  dot = (f[0] * t[0]) + (f[1] * t[1]) + (f[2] * t[2])
  if dot > 0.999999
    x = 0.0
    y = 0.0
    z = 0.0
    w = 1.0
  elsif dot < -0.999999
    if (f.z.abs < f.x.abs) && (f.z.abs < f.y.abs)
      x = (f[0] * f[2]) - (f[2] * f[1])
      y = (f[2] * f[0]) + (f[1] * f[2])
      z = (-f[1] * f[1]) - (f[0] * f[0])
    elsif f.y.abs < f.x.abs
      x = (f[1] * f[2]) - (f[0] * f[1])
      y = (f[0] * f[0]) + (f[2] * f[2])
      z = (-f[2] * f[1]) - (f[1] * f[0])
    else
      x = (-f[2] * f[2]) - (f[1] * f[1])
      y = (f[1] * f[0]) - (f[0] * f[2])
      z = (f[0] * f[1]) + (f[2] * f[0])
    end

    dot = (x * x) + (y * y) + (z * z)
    div = sqrt(dot)
    x /= div
    y /= div
    z /= div
    w = 0.0
  else
    div = sqrt((dot + 1.0) * 2.0)
    x = ((f[1] * t[2]) - (f[2] * t[1])) / div
    y = ((f[2] * t[0]) - (f[0] * t[2])) / div
    z = ((f[0] * t[1]) - (f[1] * t[0])) / div
    w = div * 0.5
  end
  return Quaternion.new([x, y, z, w])
end

.qfromc(rotation_matrix) ⇒ Quaternion

Create a quaternion from a direction-cosine matrix (rotation matrix). Reference Article: J. Spacecraft Vol.13, No.12 Dec.1976 p754



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# File 'lib/openc3/utilities/quaternion.rb', line 217

def self.qfromc(rotation_matrix)
  tracec = rotation_matrix.trace()
  p = 1.0 + tracec
  if p < 0.0
    p = 0.0
  end
  q = Quaternion.new([0.0, 0.0, 0.0, sqrt(p) / 2.0])
  if q[3] >= 0.1
    factor = 1.0 / (4.0 * q[3])
    q[0] = (rotation_matrix[1][2] - rotation_matrix[2][1]) * factor
    q[1] = (rotation_matrix[2][0] - rotation_matrix[0][2]) * factor
    q[2] = (rotation_matrix[0][1] - rotation_matrix[1][0]) * factor
  else # For rotations near 180 degrees
    q[0] = sqrt(((2.0 * rotation_matrix[0][0]) + 1.0 - tracec) / 4.0)
    q[1] = sqrt(((2.0 * rotation_matrix[1][1]) + 1.0 - tracec) / 4.0)
    q[2] = sqrt(((2.0 * rotation_matrix[2][2]) + 1.0 - tracec) / 4.0)

    i = 0
    if q[1] >= q[i]
      i = 1
    end
    if q[2] >= q[i]
      i = 2
    end
    case i
    when 0
      q[0] = q[0].abs * Quaternion.signnz(rotation_matrix[1][2] - rotation_matrix[2][1])
      q[1] = q[1].abs * Quaternion.signnz((rotation_matrix[1][0] + rotation_matrix[0][1]) * q[0])
      q[2] = q[2].abs * Quaternion.signnz((rotation_matrix[2][0] + rotation_matrix[0][2]) * q[0])
    when 1
      q[1] = q[1].abs * Quaternion.signnz(rotation_matrix[2][0] - rotation_matrix[0][2])
      q[0] = q[0].abs * Quaternion.signnz((rotation_matrix[1][0] + rotation_matrix[0][1]) * q[1])
      q[2] = q[2].abs * Quaternion.signnz((rotation_matrix[2][1] + rotation_matrix[1][2]) * q[1])
    else
      q[2] = q[2].abs * Quaternion.signnz(rotation_matrix[0][1] - rotation_matrix[1][0])
      q[0] = q[0].abs * Quaternion.signnz((rotation_matrix[0][2] + rotation_matrix[2][0]) * q[2])
      q[1] = q[1].abs * Quaternion.signnz((rotation_matrix[1][2] + rotation_matrix[2][1]) * q[2])
    end
  end

  return q
end

.signnz(value) ⇒ Float 



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# File 'lib/openc3/utilities/quaternion.rb', line 204

def self.signnz(value)
  if value >= 0.0
    return 1.0
  else
    return -1.0
  end
end

Instance Method Details

#*(other) ⇒ Quaternion Also known as: qmult 



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# File 'lib/openc3/utilities/quaternion.rb', line 120

def *(other)
  q = Quaternion.new()

  q[0] =  (@data[3] * other[0]) - (@data[2] * other[1]) +
          (@data[1] * other[2]) + (@data[0] * other[3])
  q[1] = (@data[2] * other[0]) + (@data[3] * other[1]) -
         (@data[0] * other[2]) + (@data[1] * other[3])
  q[2] = -(@data[1] * other[0]) + (@data[0] * other[1]) +
         (@data[3] * other[2]) + (@data[2] * other[3])
  q[3] = -(@data[0] * other[0]) - (@data[1] * other[1]) -
         (@data[2] * other[2]) + (@data[3] * other[3])

  return q
end

#[](index) ⇒ Float 



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# File 'lib/openc3/utilities/quaternion.rb', line 60

def [](index)
  return data[index]
end

#[]=(index, value) ⇒ Object 



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# File 'lib/openc3/utilities/quaternion.rb', line 66

def []=(index, value)
  @data[index] = value
end

#inverse ⇒ Quaternion Also known as: inv 



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# File 'lib/openc3/utilities/quaternion.rb', line 137

def inverse
  Quaternion.new([-@data[0], -@data[1], -@data[2], @data[3]])
end

#normalize ⇒ Quaternion 



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# File 'lib/openc3/utilities/quaternion.rb', line 143

def normalize
  t = (@data[0] * @data[0]) + (@data[1] * @data[1]) + (@data[2] * @data[2]) + (@data[3] * @data[3])
  if t > 0.0
    f = 1.0 / sqrt(t)
    @data[0] *= f
    @data[1] *= f
    @data[2] *= f
    @data[3] *= f
  end
  return self
end

#q0 ⇒ Float Also known as: x 



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# File 'lib/openc3/utilities/quaternion.rb', line 75

def q0
  return @data[0]
end

#q0=(value) ⇒ Object 



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# File 'lib/openc3/utilities/quaternion.rb', line 99

def q0=(value)
  @data[0] = value
end

#q1 ⇒ Float Also known as: y 



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# File 'lib/openc3/utilities/quaternion.rb', line 81

def q1
  return @data[1]
end

#q1=(value) ⇒ Object 



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# File 'lib/openc3/utilities/quaternion.rb', line 104

def q1=(value)
  @data[1] = value
end

#q2 ⇒ Float Also known as: z 



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# File 'lib/openc3/utilities/quaternion.rb', line 87

def q2
  return @data[2]
end

#q2=(value) ⇒ Object 



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# File 'lib/openc3/utilities/quaternion.rb', line 109

def q2=(value)
  @data[2] = value
end

#q3 ⇒ Float Also known as: w 



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# File 'lib/openc3/utilities/quaternion.rb', line 93

def q3
  return @data[3]
end

#q3=(value) ⇒ Object 



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# File 'lib/openc3/utilities/quaternion.rb', line 114

def q3=(value)
  @data[3] = value
end

#to_s ⇒ String 



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# File 'lib/openc3/utilities/quaternion.rb', line 54

def to_s
  "#<OpenC3::Quaternion:0x#{self.object_id.to_s(16)}> #{@data}"
end

#vecrot(vector) ⇒ Array<Float, Float, Float>

Rotate a vector using this quaternion



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# File 'lib/openc3/utilities/quaternion.rb', line 159

def vecrot(vector)
  temp_q = self.inverse * (Quaternion.new([vector[0], vector[1], vector[2], 0]) * self)
  return [temp_q[0], temp_q[1], temp_q[2]]
end