cdm/src/main/java/ucar/nc2/dataset/transform/AbstractTransformBuilder.java
protected double getEarthRadiusInKm(AttributeContainer ctv) {
    double earth_radius = readAttributeDouble(ctv, CF.EARTH_RADIUS, Earth.getRadius());
    if (earth_radius > 10000.0) earth_radius *= .001;
    return earth_radius;
  }
protected double getEarthRadiusInKm(AttributeContainer ctv) {
    double earth_radius = readAttributeDouble(ctv, CF.EARTH_RADIUS, Earth.getRadius());
    if (earth_radius > 10000.0) earth_radius *= .001;
    return earth_radius;
  }
Get the earth radius in km from the attribute "earth_radius".
Normally this is in meters, convert to km if its > 10,000.
Use Earth.getRadius() as default.

@param ctv coord transform variable
@return earth radius in km