<simpleType name="PositiveDirectionEnumType">
  <annotation>
    <documentation>Convention for the positive direction of measurement along a linear feature. In DIGGS, measurement always proceeds from first to last coordinate, but this allows semantic labeling. These are primarily semantic labels that clarify the meaning of "increasing" measurements without changing the fundamental coordinate order basis.</documentation>
  </annotation>
  <restriction base="string">
    <enumeration value="increasing">
      <annotation>
        <documentation>Positive direction follows coordinate order from first to last. This is the DIGGS standard and default convention.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="downward">
      <annotation>
        <documentation>Semantic label indicating positive is downward (deeper). Common for boreholes where first coordinate is collar and last is bottom of hole. Measurements increase with depth.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="upward">
      <annotation>
        <documentation>Semantic label indicating positive is upward (shallower). May be used for core logging from bottom to top, or for elevation-based referencing systems.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="forward">
      <annotation>
        <documentation>Semantic label for horizontal features indicating positive is in the forward direction of survey or alignment. Common for transects, pipelines, and tracklines.</documentation>
      </annotation>
    </enumeration>
  </restriction>
</simpleType>