def getScaledValue(vf, tag, value):
    """Answers the scaled value for the "tag" axis, where value (-1..0..1) is
    upscaled to ratio in (minValue, defaultValue, maxValue)."""
    if not tag in vf.axes:
        return None
    assert -1 <= value <= 1
    minValue, defaultValue, maxValue = vf.axes[tag]
    if not value:
        return defaultValue
    if value < 0:
        return defaultValue + (defaultValue - minValue) * value
    return defaultValue + (maxValue - defaultValue) * value
