<simpleType name="OffsetDirectionEnumType">
  <annotation>
    <documentation>Direction of lateral offset from a LinearExtent centerline. The direction is determined relative to looking along the LinearElement in the direction from first coordinate to last coordinate in gml:posList. Positive offset values are in the specified direction. Negative offset values are in the opposite direction. Zero offset is on the centerline.</documentation>
  </annotation>
  <restriction base="string">
    <enumeration value="right">
      <annotation>
        <documentation>Positive offset is to the right when looking along the LinearElement from first to last coordinate. Standard for terrestrial applications (transects, pipelines, road alignments).</documentation>
      </annotation>
    </enumeration>
    <enumeration value="left">
      <annotation>
        <documentation>Positive offset is to the left when looking along the LinearElement from first to last coordinate. Less common but available if the application prefers left-positive convention.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="starboard">
      <annotation>
        <documentation>Positive offset is to starboard (right side when facing bow/forward direction). Marine convention for geophysical tracklines and marine surveys. Equivalent to "right" but uses nautical terminology for consistency with marine operations.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="port">
      <annotation>
        <documentation>Positive offset is to port (left side when facing bow/forward direction). Marine convention for geophysical tracklines. Equivalent to "left" but uses nautical terminology. Less common as most marine systems use starboard-positive convention.</documentation>
      </annotation>
    </enumeration>
  </restriction>
</simpleType>