Converts ounces per linear yard (a common measurement of fabric density in North America) to GSM (grams per square meter)

oz_per_linear_yd_to_gsm.rb

# Converts ounces per linear yard (a common measurement of fabric density in 
# North America) to GSM (grams per square meter).
# 
# When buying fabric, a "linear yard" refers to a yard-long piece of fabric cut 
# from a bolt. Ounces per linear yard are calculated by weighing a bolt of 
# fabric, then dividing its weight by its length in yards when fully unspooled. 
# Fabric bolts may be of varying heights, but are generally more than 1 yard 
# tall; 4-5 feet is a common height.
# 
# (Q) Given this variability in bolt size, why do so many vendors describe 
# fabric weights using oz/linear yd, rather than converting to a more-useful 
# measure like oz/sq yd?
# 
# (A) Well, you see, {{DMCA TAKEDOWN}}
#
# @param [Numeric] oz_p_linear_yd   Weight of 1 yd fabric cut from bolt
# @param [Numeric] width_in_yd      Height of fabric bolt in question
# @return [Float]                   Grams per square meter
def oz_per_linear_yd_to_gsm(oz_p_linear_yd=8.5, width_in_yd=(60.0/36))
  width_in_m = yd_to_m(width_in_yd)
  area_in_m = yd_to_m(1.0) * width_in_m
  weight_in_g = oz_to_g(oz_p_linear_yd)
  return weight_in_g.to_f / area_in_m.to_f
end
alias :oly_to_gsm :oz_per_linear_yd_to_gsm


# Ounces per linear yard => Ounces per square yard
#
# @param [Numeric] oz_p_linear_yd   Ounces per linear yard
# @param [Numeric] width_in_in      Height of fabric bolt in question
# @return [Float]                   Ounces per square yard (oz/yd²)
def oz_p_linear_yd_to_oz_p_sqyd(oz_p_linear_yd=8.5, width_in_in=60)
  width_in_yd = in_to_yd(width_in_in)
  return oz_p_linear_yd / width_in_yd
end
alias :oly_to_osy :oz_p_linear_yd_to_oz_p_sqyd


# Ounces per square yard => Grams per square meter
#
# @param [Numeric] oz_p_sqyd        Ounces per square yard (oz/yd²)
# @return [Float]                   Grams per square meter (GSM or g/m²)
def oz_p_sqyd_to_g_p_sqm(oz_p_sqyd=5.1)
  weight_in_g = oz_to_g(oz_p_sqyd)
  width_in_m = yd_to_m(1.0)
  area_in_sqm = width_in_m * width_in_m
  return weight_in_g / area_in_sqm
end
alias :osy_to_gsm :oz_p_sqyd_to_g_p_sqm


# HELPERS

VALUES = {
  m_per_yd: 0.9144, 
  g_per_oz: 28.34952, 
  in_per_yd: 36.0, 
}

def yd_to_m(val)
  val * VALUES[:m_per_yd]
end
def m_to_yd(val)
  val / VALUES[:m_per_yd]
end

def oz_to_g(val)
  val * VALUES[:g_per_oz]
end
def g_to_oz(val)
  val / VALUES[:g_per_oz]
end

def yd_to_in(val)
  val * VALUES[:in_per_yd]
end
def in_to_yd(val)
  val / VALUES[:in_per_yd]
end