Package org.djunits.unit.scale

Class OffsetLinearScale

  • All Implemented Interfaces:
    Serializable, Scale
    public class OffsetLinearScale
extends LinearScale
    Scale with factor and zero point offset.

    A Scale for linear transformations with an offset that has to be applied first when converting to the standard (SI) unit, before the scaling takes place, e.g. for Temperature. As an example, transform from Degrees Fahrenheit to Kelvin (SI). The conversion is K = (F + 459.67) × 5⁄9, and F = K × 9⁄5 − 459.67.

    When we have an original scale with offset o1 and scalefactor f1, the calculation to the base unit is 

     valueSI = (value1 + o1) * f1

    So the offset is expressed in the "unit" of the value. As an example, when we transform degrees Fahrenheit to Kelvin, the factor is 5/9, and the offset is 459.67 (degrees Fahrenheit of 0 degrees Fahrenheit expressed in Kelvin). The formula becomes: K = (F + 459.67) * 5/9. So 0 F is 459.67 * 5/9 = 255.372 K. For Celcius to Kelvin, the scale factor is 1, and the offset 273.15. From Fahrenheit to Celcius, the offset is -32, and the factor is 5/9.

    When we apply a second offset transformation on a scale, e.g. from Fahrenheit to Celcius to Kelvin, this works as follows: If we combine a second scale factor for a derived unit with offset o2 and scalefactor f2, we need to calculate the ultimate scale to the base (si) unit. The factor then becomes: 

     value1  = (value2 + o2) * f2
 valueSI = (value1 + o1) * f1 = value2 * (f1 * f2) + (f1 * f2 * o2 + f1 * o1)

    as an example for F --2--> C --1--> K: o1 = 273.15, f1 = 1, o2 = -32, f2 = 5/9:
    110 F = 110*5/9 -32*5/9 + 273.15 = 316.483 K.

    Copyright (c) 2013-2020 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved.
    BSD-style license. See OpenTrafficSim License.

    Author:
    Alexander Verbraeck, Peter Knoppers
    See Also:
    Serialized Form

    • Constructor Detail

      • OffsetLinearScale

        public OffsetLinearScale​(double conversionFactorToStandardUnit,
                         double offsetToStandardUnit)
        Construct a Scale for linear transformations with an offset, e.g. for Temperature.
        Parameters:
        conversionFactorToStandardUnit - double; the conversion factor by which this number has to be multiplied to convert it to the standard (e.g., SI) unit.
        offsetToStandardUnit - the offset that has to be taken into account for conversions; when converting to a standard unit, the offset is applied first.

    • Method Detail

      • toStandardUnit

        public final double toStandardUnit​(double value)
        Convert a value to an SI value using this scale.
        Specified by:
        toStandardUnit in interface Scale
        Overrides:
        toStandardUnit in class LinearScale
        Parameters:
        value - double; the value to convert
        Returns:
        the corresponding SI value

      • fromStandardUnit

        public final double fromStandardUnit​(double value)
        Convert a value from an SI value to a value in the unit that uses this scale.
        Specified by:
        fromStandardUnit in interface Scale
        Overrides:
        fromStandardUnit in class LinearScale
        Parameters:
        value - double; the value to convert
        Returns:
        the corresponding value in the given unit

      • getOffsetToStandardUnit

        public final double getOffsetToStandardUnit()
        Retrieve the offset from the standard unit.
        Returns:
        double; the offset from the standard unit

      • isBaseSIScale

        public boolean isBaseSIScale()
        Return whether a scale is a 'standard' scale that would belong to an SI unit. For a linear scale, any scale with conversion factor 1 would be considered standard. For an offset scale, it would be considered standard if the offset is 0 and the conversion factor is 1.
        Specified by:
        isBaseSIScale in interface Scale
        Overrides:
        isBaseSIScale in class LinearScale
        Returns:
        boolean; whether the scale is a 'standard' scale that would belong to an SI unit.