Understanding why converting using aliases fails

[keitheweber]

I wrote a simple set of unit tests that would test converting from one unit to another when instantiating the unit objects by parsing a string. I am not sure what I am doing wrong, but most of these fail. It appears that the alias names defined in https://www.unidata.ucar.edu/software/udunits/udunits-2.2.28/udunits2-common.xml are not being honored?

Here's the source code for the unit tests

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.DynamicTest;
import org.junit.jupiter.api.TestFactory;
import ucar.units.Converter;
import ucar.units.Unit;
import ucar.units.UnitFormatManager;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

class ConversionTest {

    @TestFactory
    Stream<DynamicTest> conversionTests() {
        String[] unitNames = new String[]{
                "degK",
                "K",
                "deg_K",
                "degsK",
                "F",
                "deg_F",
                "degF",
                "C",
                "degC",
                "deg_C"
        };

        List<Unit> units = Arrays.stream(unitNames)
                .map(this::parse)
                .collect(Collectors.toList());

        return IntStream.range(0, units.size())
                .mapToObj(fromIndex -> IntStream.range(0, units.size())
                        .mapToObj(toIndex ->
                                DynamicTest.dynamicTest(unitNames[fromIndex] + " to " + unitNames[toIndex],
                                        () -> Assertions.assertDoesNotThrow(() -> convertTest(units.get(fromIndex), units.get(toIndex), 10.0)))
                        ).collect(Collectors.toList()))
                .flatMap(List::stream);
    }

    private double convertTest(Unit from, Unit to, double value) {
        try {
            if (!from.isCompatible(to)) {
                throw new RuntimeException("Units not compatible");
            }
            Converter converter = from.getConverterTo(to);
            return converter.convert(value);
        } catch (Exception ex) {
            throw new RuntimeException("Failed to convert", ex);
        }
    }

    private Unit parse(String name) {
        try {
            return UnitFormatManager.instance().parse(name);
        } catch (Exception e) {
            throw new RuntimeException("Failed to parse", e);
        }
    }
}

[lesserwhirls]

This is a bug, for sure. It looks like the unit aliases in the java udunits package are not up-to-date with the C library.

Specifically here:

netcdf-java/udunits/src/main/java/ucar/units/StandardUnitDB.java

Lines 113 to 138 in 6704deb

	aa("degree Kelvin", "kelvin", "degrees Kelvin");
	aa("degreeK", "kelvin", "degreesK");
	aa("degree K", "kelvin", "degrees K");
	aa("Celsius", "degree_Celsius");
	aa("degreeC", "degree_Celsius", "degreesC");
	aa("degree C", "degree_Celsius", "degrees C");
	aa("degree centigrade", "degree_Celsius", "degrees centigrade");
	aa("centigrade", "degree_Celsius");
	aa("degree Rankine", "rankine", "degrees Rankine");
	aa("degreeR", "rankine", "degreesR");
	aa("degree R", "rankine", "degrees R");
	aa("degree Fahrenheit", "fahrenheit", "degrees Fahrenheit");
	aa("degreeF", "fahrenheit", "degreesF");
	aa("degree F", "fahrenheit", "degrees F");
	as("degK", "kelvin");
	as("deg K", "kelvin");
	as("degC", "degree_Celsius");
	as("deg C", "degree_Celsius");
	as("degR", "rankine");
	as("deg R", "rankine");
	as("degF", "fahrenheit");
	as("deg F", "fahrenheit");

[keitheweber]

@lesserwhirls Thanks for the quick reply. I created an issue from this discussion to track it. I wanted to reach out to see if this is something that could be worked any time soon?

[lesserwhirls]

I am working on a release at the moment, and could likely get the temperature related aliases in. A full review, however, won't be possible until after the release.