gml:ArcStringByBulge 

This variant of the arc computes the mid points of the arcs instead of storing the coordinates directly. The control point sequence consists of the start and end points of each arc plus the bulge (see ISO 19107:2003, 6.4.17.2). The normal is a vector normal (perpendicular) to the chord of the arc (see ISO 19107:2003, 6.4.17.4).
The interpolation is fixed as "circularArc2PointWithBulge".
The number of arcs in the arc string may be explicitly stated in the attribute numArc. The number of control points in the arc string shall be numArc + 1.
The content model follows the general pattern for the encoding of curve segments.

Element Information

Model

(gml:pos | gml:pointProperty | gml:pointRep | gml:posList | gml:coordinates) , gml:bulge+ , gml:normal+
Children: gml:bulge, gml:coordinates, gml:normal, gml:pointProperty, gml:pointRep, gml:pos, gml:posList

Attributes

QName Type Fixed Default Use Inheritable Annotation
interpolation gml:CurveInterpolationType circularArc2PointWithBulge optional
numArc integer optional
numDerivativeInterior integer 0 optional
numDerivativesAtEnd integer 0 optional
numDerivativesAtStart integer 0 optional

Source 

<element name="ArcStringByBulge" type="gml:ArcStringByBulgeType" substitutionGroup="gml:AbstractCurveSegment">
  <annotation>
    <documentation>This variant of the arc computes the mid points of the arcs instead of storing the coordinates directly. The control point sequence consists of the start and end points of each arc plus the bulge (see ISO 19107:2003, 6.4.17.2). The normal is a vector normal (perpendicular) to the chord of the arc (see ISO 19107:2003, 6.4.17.4). The interpolation is fixed as "circularArc2PointWithBulge". The number of arcs in the arc string may be explicitly stated in the attribute numArc. The number of control points in the arc string shall be numArc + 1. The content model follows the general pattern for the encoding of curve segments.</documentation>
  </annotation>
</element>

Sample