OffsetLinearScale.java
package org.djunits.unit.scale;
/**
* Scale with factor and zero point offset.
* <p>
* 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.
* </p>
* <p>
* When we have an original scale with offset o1 and scalefactor f1, the calculation to the base unit is
*
* <pre>
* valueSI = (value1 + o1) * f1
* </pre>
* <p>
* 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.
* </p>
* <p>
* 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:
*
* <pre>
* value1 = (value2 + o2) * f2
* valueSI = (value1 + o1) * f1 = value2 * (f1 * f2) + (f1 * f2 * o2 + f1 * o1)
* </pre>
* <p>
* as an example for F --2--> C --1--> K: o1 = 273.15, f1 = 1, o2 = -32, f2 = 5/9: <br>
* 110 F = 110*5/9 -32*5/9 + 273.15 = 316.483 K.
* </p>
* <p>
* Copyright (c) 2013-2024 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
* BSD-style license. See <a href="https://djunits.org/docs/license.html">DJUNITS License</a>.
* </p>
* @author <a href="https://www.tudelft.nl/averbraeck">Alexander Verbraeck</a>
* @author <a href="https://www.tudelft.nl/staff/p.knoppers/">Peter Knoppers</a>
*/
public class OffsetLinearScale extends LinearScale
{
/** */
private static final long serialVersionUID = 20151011L;
/** The offset that has to be taken into account for conversions, multiplied by the conversionFactorToStandardUnit. */
private final double offsetToStandardUnit;
/**
* Construct a Scale for linear transformations with an offset, e.g. for Temperature.
* @param conversionFactorToStandardUnit double; the conversion factor by which this number has to be multiplied to convert
* it to the standard (e.g., SI) unit.
* @param offsetToStandardUnit the offset that has to be taken into account for conversions; when converting to a standard
* unit, the offset is applied first.
*/
public OffsetLinearScale(final double conversionFactorToStandardUnit, final double offsetToStandardUnit)
{
super(conversionFactorToStandardUnit);
this.offsetToStandardUnit = offsetToStandardUnit;
}
@Override
public final double toStandardUnit(final double value)
{
return (value + this.offsetToStandardUnit) * getConversionFactorToStandardUnit();
}
@Override
public final double fromStandardUnit(final double value)
{
return value / getConversionFactorToStandardUnit() - this.offsetToStandardUnit;
}
/**
* Retrieve the offset from the standard unit.
* @return double; the offset from the standard unit
*/
public final double getOffsetToStandardUnit()
{
return this.offsetToStandardUnit;
}
@Override
public boolean isBaseSIScale()
{
return super.isBaseSIScale() && this.offsetToStandardUnit == 0.0;
}
@Override
public int hashCode()
{
final int prime = 31;
int result = super.hashCode();
long temp;
temp = Double.doubleToLongBits(this.offsetToStandardUnit);
result = prime * result + (int) (temp ^ (temp >>> 32));
return result;
}
@SuppressWarnings("checkstyle:needbraces")
@Override
public boolean equals(final Object obj)
{
if (this == obj)
return true;
if (!super.equals(obj))
return false;
if (getClass() != obj.getClass())
return false;
OffsetLinearScale other = (OffsetLinearScale) obj;
if (Double.doubleToLongBits(this.offsetToStandardUnit) != Double.doubleToLongBits(other.offsetToStandardUnit))
return false;
return true;
}
@Override
public String toString()
{
return "OffsetLinearScale [offsetToStandardUnit=" + this.offsetToStandardUnit + ", conversionFactorToStandardUnit="
+ this.getConversionFactorToStandardUnit() + "]";
}
}