package org.opentrafficsim.road.network.lane;
   
   import java.io.Serializable;
   import java.util.ArrayList;
   import java.util.Arrays;
   import java.util.Iterator;
   import java.util.List;
   
   import org.djunits.value.vdouble.scalar.Length;
  import org.djutils.event.LocalEventProducer;
  import org.djutils.exceptions.Throw;
  import org.djutils.exceptions.Try;
  import org.djutils.logger.CategoryLogger;
  import org.opentrafficsim.base.Identifiable;
  import org.opentrafficsim.core.animation.Drawable;
  import org.opentrafficsim.core.geometry.Bezier;
  import org.opentrafficsim.core.geometry.Bounds;
  import org.opentrafficsim.core.geometry.DirectedPoint;
  import org.opentrafficsim.core.geometry.OtsGeometryException;
  import org.opentrafficsim.core.geometry.OtsLine3d;
  import org.opentrafficsim.core.geometry.OtsPoint3d;
  import org.opentrafficsim.core.geometry.OtsShape;
  import org.opentrafficsim.core.network.LateralDirectionality;
  import org.opentrafficsim.core.network.NetworkException;
  import org.opentrafficsim.road.network.RoadNetwork;
  
  import nl.tudelft.simulation.dsol.animation.Locatable;
  
  /**
   * Cross section elements are used to compose a CrossSectionLink.
   * <p>
   * Copyright (c) 2013-2023 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
   * </p>
   * @author <a href="https://github.com/averbraeck">Alexander Verbraeck</a>
   * @author <a href="https://tudelft.nl/staff/p.knoppers-1">Peter Knoppers</a>
   * @author <a href="https://www.citg.tudelft.nl">Guus Tamminga</a>
   */
  public class CrossSectionElement extends LocalEventProducer implements Locatable, Serializable, Identifiable, Drawable
  {
      /** */
      private static final long serialVersionUID = 20150826L;
  
      /** The id. Should be unique within the parentLink. */
      private final String id;
  
      /** Cross Section Link to which the element belongs. */
      @SuppressWarnings("checkstyle:visibilitymodifier")
      protected final CrossSectionLink parentLink;
  
      /** The offsets and widths at positions along the line, relative to the design line of the parent link. */
      @SuppressWarnings("checkstyle:visibilitymodifier")
      protected final List<CrossSectionSlice> crossSectionSlices;
  
      /** The length of the line. Calculated once at the creation. */
      @SuppressWarnings("checkstyle:visibilitymodifier")
      protected final Length length;
  
      /** The center line of the element. Calculated once at the creation. */
      private final OtsLine3d centerLine;
  
      /** The contour of the element. Calculated once at the creation. */
      private final OtsShape contour;
  
      /** Maximum direction difference w.r.t. node direction at beginning and end of a CrossSectionElement. */
      public static final double MAXIMUMDIRECTIONERROR = Math.toRadians(0.1);
  
      /**
       * At what fraction of the first segment will an extra point be inserted if the <code>MAXIMUMDIRECTIONERROR</code> is
       * exceeded.
       */
      public static final double FIXUPPOINTPROPORTION = 1.0 / 3;
  
      /**
       * Construct a new CrossSectionElement. <b>Note:</b> LEFT is seen as a positive lateral direction, RIGHT as a negative
       * lateral direction, with the direction from the StartNode towards the EndNode as the longitudinal direction.
       * @param id String; The id of the CrossSectionElement. Should be unique within the parentLink.
       * @param parentLink CrossSectionLink; Link to which the element belongs.
       * @param crossSectionSlices List&lt;CrossSectionSlice&gt;; the offsets and widths at positions along the line, relative to
       *            the design line of the parent link. If there is just one with and offset, there should just be one element in
       *            the list with Length = 0. If there are more slices, the last one should be at the length of the design line.
       *            If not, a NetworkException is thrown.
       * @throws OtsGeometryException when creation of the geometry fails
       * @throws NetworkException when id equal to null or not unique, or there are multiple slices and the last slice does not
       *             end at the length of the design line.
       */
      public CrossSectionElement(final CrossSectionLink parentLink, final String id,
              final List<CrossSectionSlice> crossSectionSlices) throws OtsGeometryException, NetworkException
      {
          Throw.when(parentLink == null, NetworkException.class,
                  "Constructor of CrossSectionElement for id %s, parentLink cannot be null", id);
          Throw.when(id == null, NetworkException.class, "Constructor of CrossSectionElement -- id cannot be null");
          for (CrossSectionElement cse : parentLink.getCrossSectionElementList())
          {
              Throw.when(cse.getId().equals(id), NetworkException.class,
                      "Constructor of CrossSectionElement -- id %s not unique within the Link", id);
          }
          Throw.whenNull(crossSectionSlices, "crossSectionSlices may not be null");
          this.id = id;
         this.parentLink = parentLink;
 
         this.crossSectionSlices = new ArrayList<>(crossSectionSlices); // copy of list with immutable slices
         Throw.when(this.crossSectionSlices.size() == 0, NetworkException.class,
                 "CrossSectionElement %s is created with zero slices for %s", id, parentLink);
         Throw.when(this.crossSectionSlices.get(0).getRelativeLength().si != 0.0, NetworkException.class,
                 "CrossSectionElement %s for %s has a first slice with relativeLength is not equal to 0.0", id, parentLink);
         Throw.when(
                 this.crossSectionSlices.size() > 1 && this.crossSectionSlices.get(this.crossSectionSlices.size() - 1)
                         .getRelativeLength().ne(this.parentLink.getLength()),
                 NetworkException.class, "CrossSectionElement %s for %s has a last slice with relativeLength is not equal "
                         + "to the length of the parent link",
                 id, parentLink);
         OtsLine3d proposedCenterLine = null;
         if (this.crossSectionSlices.size() <= 2)
         {
             proposedCenterLine = fixTightInnerCurve(new double[] {0.0, 1.0},
                     new double[] {getDesignLineOffsetAtBegin().getSI(), getDesignLineOffsetAtEnd().getSI()});
         }
         else
         {
             double[] fractions = new double[this.crossSectionSlices.size()];
             double[] offsets = new double[this.crossSectionSlices.size()];
             for (int i = 0; i < this.crossSectionSlices.size(); i++)
             {
                 fractions[i] = this.crossSectionSlices.get(i).getRelativeLength().si / this.parentLink.getLength().si;
                 offsets[i] = this.crossSectionSlices.get(i).getDesignLineOffset().si;
             }
             proposedCenterLine = fixTightInnerCurve(fractions, offsets);
         }
         // Make positions and directions of begin and end of CrossSection exact
         List<OtsPoint3d> points = new ArrayList<OtsPoint3d>(Arrays.asList(proposedCenterLine.getPoints()));
         // Make position at begin exact
         DirectedPoint linkFrom = Try.assign(() -> parentLink.getStartNode().getLocation(), "Cannot happen");
         double fromDirection = linkFrom.getRotZ();
         points.remove(0);
         points.add(0, new OtsPoint3d(linkFrom.x + getDesignLineOffsetAtBegin().getSI() * Math.cos(fromDirection + Math.PI / 2),
                 linkFrom.y + getDesignLineOffsetAtBegin().getSI() * Math.sin(fromDirection + Math.PI / 2)));
         // Make position at end exact
         DirectedPoint linkTo = Try.assign(() -> parentLink.getEndNode().getLocation(), "Cannot happen");
         double toDirection = linkTo.getRotZ();
         points.remove(points.size() - 1);
         points.add(new OtsPoint3d(linkTo.x + getDesignLineOffsetAtEnd().getSI() * Math.cos(toDirection + Math.PI / 2),
                 linkTo.y + getDesignLineOffsetAtEnd().getSI() * Math.sin(toDirection + Math.PI / 2)));
         // Check direction at begin
         double direction = points.get(0).horizontalDirectionSI(points.get(1));
         OtsPoint3d extraPointAfterStart = null;
         if (Math.abs(direction - fromDirection) > MAXIMUMDIRECTIONERROR)
         {
             // Insert an extra point to ensure that the new CrossSectionElement starts off in the right direction
             OtsPoint3d from = points.get(0);
             OtsPoint3d next = points.get(1);
             double distance =
                     Math.min(from.horizontalDistanceSI(next) * FIXUPPOINTPROPORTION, crossSectionSlices.get(0).getWidth().si);
             extraPointAfterStart = new OtsPoint3d(from.x + Math.cos(fromDirection) * distance,
                     from.y + Math.sin(fromDirection) * distance, from.z + FIXUPPOINTPROPORTION * (next.z - from.z));
             // Do not insert it yet because that could cause a similar point near the end to be put at the wrong distance
         }
         // Check direction at end
         int pointCount = points.size();
         direction = points.get(pointCount - 2).horizontalDirectionSI(points.get(pointCount - 1));
         if (Math.abs(direction - toDirection) > MAXIMUMDIRECTIONERROR)
         {
             // Insert an extra point to ensure that the new CrossSectionElement ends in the right direction
             OtsPoint3d to = points.get(pointCount - 1);
             OtsPoint3d before = points.get(pointCount - 2);
             double distance = Math.min(before.horizontalDistanceSI(to) * FIXUPPOINTPROPORTION,
                     crossSectionSlices.get(Math.max(0, crossSectionSlices.size() - 2)).getWidth().si);
             points.add(pointCount - 1, new OtsPoint3d(to.x - Math.cos(toDirection) * distance,
                     to.y - Math.sin(toDirection) * distance, to.z - FIXUPPOINTPROPORTION * (before.z - to.z)));
         }
         if (null != extraPointAfterStart)
         {
             points.add(1, extraPointAfterStart);
         }
         this.centerLine = new OtsLine3d(points);
         this.length = this.centerLine.getLength();
         this.contour = constructContour(this);
         this.parentLink.addCrossSectionElement(this);
 
         // clear lane change info cache for each cross section element created
         parentLink.getNetwork().clearLaneChangeInfoCache();
     }
 
     /**
      * <b>Note:</b> LEFT is seen as a positive lateral direction, RIGHT as a negative lateral direction, with the direction from
      * the StartNode towards the EndNode as the longitudinal direction.
      * @param id String; The id of the CrossSectionElement. Should be unique within the parentLink.
      * @param parentLink CrossSectionLink; Link to which the element belongs.
      * @param lateralOffsetAtBegin Length; the lateral offset of the design line of the new CrossSectionLink with respect to the
      *            design line of the parent Link at the start of the parent Link
      * @param lateralOffsetAtEnd Length; the lateral offset of the design line of the new CrossSectionLink with respect to the
      *            design line of the parent Link at the end of the parent Link
      * @param beginWidth Length; width at start, positioned <i>symmetrically around</i> the design line
      * @param endWidth Length; width at end, positioned <i>symmetrically around</i> the design line
      * @param fixGradualLateralOffset boolean; true if gradualLateralOffset needs to be fixed
      * @throws OtsGeometryException when creation of the geometry fails
      * @throws NetworkException when id equal to null or not unique
      */
     public CrossSectionElement(final CrossSectionLink parentLink, final String id, final Length lateralOffsetAtBegin,
             final Length lateralOffsetAtEnd, final Length beginWidth, final Length endWidth,
             final boolean fixGradualLateralOffset) throws OtsGeometryException, NetworkException
     {
         this(parentLink, id, fixLateralOffset(parentLink, lateralOffsetAtBegin, lateralOffsetAtEnd, beginWidth, endWidth,
                 fixGradualLateralOffset));
     }
 
     /**
      * Construct a list of cross section slices, using sinusoidal interpolation for changing lateral offset.
      * @param parentLink CrossSectionLink; Link to which the element belongs.
      * @param lateralOffsetAtBegin Length; the lateral offset of the design line of the new CrossSectionLink with respect to the
      *            design line of the parent Link at the start of the parent Link
      * @param lateralOffsetAtEnd Length; the lateral offset of the design line of the new CrossSectionLink with respect to the
      *            design line of the parent Link at the end of the parent Link
      * @param beginWidth Length; width at start, positioned <i>symmetrically around</i> the design line
      * @param endWidth Length; width at end, positioned <i>symmetrically around</i> the design line
      * @param fixGradualLateralOffset boolean; true if gradualLateralOffset needs to be fixed
      * @return List&ltCrossSectionSlice&gt;; the cross section slices
      */
     private static List<CrossSectionSlice> fixLateralOffset(final CrossSectionLink parentLink,
             final Length lateralOffsetAtBegin, final Length lateralOffsetAtEnd, final Length beginWidth, final Length endWidth,
             final boolean fixGradualLateralOffset)
     {
         List<CrossSectionSlice> result = new ArrayList<>();
         int numPoints = !fixGradualLateralOffset ? 2 : lateralOffsetAtBegin.equals(lateralOffsetAtEnd) ? 2 : 16;
         Length parentLength = parentLink.getLength();
         for (int index = 0; index < numPoints; index++)
         {
             double fraction = index * 1.0 / (numPoints - 1);
             Length lengthAtCrossSection = parentLength.times(fraction);
             double relativeOffsetAtFraction = (1 + Math.sin((fraction - 0.5) * Math.PI)) / 2;
             Length offsetAtFraction = Length.interpolate(lateralOffsetAtBegin, lateralOffsetAtEnd, relativeOffsetAtFraction);
             result.add(new CrossSectionSlice(lengthAtCrossSection, offsetAtFraction,
                     Length.interpolate(beginWidth, endWidth, fraction)));
         }
         return result;
     }
 
     /**
      * Returns the center line for this cross section element by adhering to the given offsets relative to the link design line.
      * This method will create a Bezier curve, ignoring the link design line, if the offset at any vertex is larger than the
      * radius, and on the inside of the curve.
      * @param fractions double[]; length fractions of offsets
      * @param offsets double[]; offsets
      * @return OtsPoint3d; center line
      * @throws OtsGeometryException index out of bounds
      */
     private OtsLine3d fixTightInnerCurve(final double[] fractions, final double[] offsets) throws OtsGeometryException
     {
         OtsLine3d linkCenterLine = getParentLink().getDesignLine();
         for (int i = 1; i < linkCenterLine.size() - 1; i++)
         {
             double fraction = linkCenterLine.getVertexFraction(i);
             int index = 0;
             while (index < fractions.length - 2 && fraction > fractions[index + 1])
             {
                 index++;
             }
             double w = (fraction - fractions[index]) / (fractions[index + 1] - fractions[index]);
             double offset = (1.0 - w) * offsets[index] + w * offsets[index + 1];
             double radius = 1.0;
             try
             {
                 radius = linkCenterLine.getProjectedVertexRadius(i).si;
             }
             catch (Exception e)
             {
                 CategoryLogger.always().error(e, "fixTightInnerCurve.getVertexFraction for " + linkCenterLine);
             }
             if ((!Double.isNaN(radius))
                     && ((radius < 0.0 && offset < 0.0 && offset < radius) || (radius > 0.0 && offset > 0.0 && offset > radius)))
             {
                 double offsetStart = getDesignLineOffsetAtBegin().getSI();
                 double offsetEnd = getDesignLineOffsetAtEnd().getSI();
                 DirectedPoint start = linkCenterLine.getLocationFraction(0.0);
                 DirectedPoint end = linkCenterLine.getLocationFraction(1.0);
                 start = new DirectedPoint(start.x - Math.sin(start.getRotZ()) * offsetStart,
                         start.y + Math.cos(start.getRotZ()) * offsetStart, start.z, start.getRotX(), start.getRotY(),
                         start.getRotZ());
                 end = new DirectedPoint(end.x - Math.sin(end.getRotZ()) * offsetEnd,
                         end.y + Math.cos(end.getRotZ()) * offsetEnd, end.z, end.getRotX(), end.getRotY(), end.getRotZ());
                 while (this.crossSectionSlices.size() > 2)
                 {
                     this.crossSectionSlices.remove(1);
                 }
                 return Bezier.cubic(start, end);
             }
         }
         if (this.crossSectionSlices.size() <= 2)
         {
             OtsLine3d designLine = this.getParentLink().getDesignLine();
             if (designLine.size() > 2)
             {
                 // TODO: this produces near-duplicate points on lane 925_J1.FORWARD1 in the Aimsun network
                 // hack: clean nearby points
                 OtsLine3d line =
                         designLine.offsetLine(getDesignLineOffsetAtBegin().getSI(), getDesignLineOffsetAtEnd().getSI());
                 List<OtsPoint3d> points = new ArrayList<>(Arrays.asList(line.getPoints()));
                 Iterator<OtsPoint3d> it = points.iterator();
                 OtsPoint3d prevPoint = null;
                 while (it.hasNext())
                 {
                     OtsPoint3d point = it.next();
                     if (prevPoint != null && prevPoint.distance(point).si < 1e-4)
                     {
                         it.remove();
                     }
                     prevPoint = point;
                 }
                 return new OtsLine3d(points);
             }
             else
             {
                 DirectedPoint refStart = getParentLink().getStartNode().getLocation();
                 double startRot = refStart.getRotZ();
                 double startOffset = this.crossSectionSlices.get(0).getDesignLineOffset().si;
                 OtsPoint3d start = new OtsPoint3d(refStart.x - Math.sin(startRot) * startOffset,
                         refStart.y + Math.cos(startRot) * startOffset, refStart.z);
                 DirectedPoint refEnd = getParentLink().getEndNode().getLocation();
                 double endRot = refEnd.getRotZ();
                 double endOffset = this.crossSectionSlices.get(this.crossSectionSlices.size() - 1).getDesignLineOffset().si;
                 OtsPoint3d end = new OtsPoint3d(refEnd.x - Math.sin(endRot) * endOffset,
                         refEnd.y + Math.cos(endRot) * endOffset, refEnd.z);
                 return new OtsLine3d(start, end);
             }
         }
         else
         {
             for (int i = 0; i < this.crossSectionSlices.size(); i++)
             {
                 fractions[i] = this.crossSectionSlices.get(i).getRelativeLength().si / this.parentLink.getLength().si;
                 offsets[i] = this.crossSectionSlices.get(i).getDesignLineOffset().si;
             }
             return this.getParentLink().getDesignLine().offsetLine(fractions, offsets);
         }
     }
 
     /**
      * <b>Note:</b> LEFT is seen as a positive lateral direction, RIGHT as a negative lateral direction, with the direction from
      * the StartNode towards the EndNode as the longitudinal direction.
      * @param id String; The id of the CrosssSectionElement. Should be unique within the parentLink.
      * @param parentLink CrossSectionLink; Link to which the element belongs.
      * @param lateralOffset Length; the lateral offset of the design line of the new CrossSectionLink with respect to the design
      *            line of the parent Link
      * @param width Length; width, positioned <i>symmetrically around</i> the design line
      * @throws OtsGeometryException when creation of the geometry fails
      * @throws NetworkException when id equal to null or not unique
      */
     public CrossSectionElement(final CrossSectionLink parentLink, final String id, final Length lateralOffset,
             final Length width) throws OtsGeometryException, NetworkException
     {
         this(parentLink, id, Arrays.asList(new CrossSectionSlice[] {new CrossSectionSlice(Length.ZERO, lateralOffset, width)}));
     }
 
     /**
      * @return parentLink.
      */
     public final CrossSectionLink getParentLink()
     {
         return this.parentLink;
     }
 
     /**
      * @return the road network to which the lane belongs
      */
     public final RoadNetwork getNetwork()
     {
         return this.parentLink.getNetwork();
     }
 
     /**
      * Calculate the slice the fractional position is in.
      * @param fractionalPosition double; the fractional position between 0 and 1 compared to the design line
      * @return int; the lower slice number between 0 and number of slices - 1.
      */
     private int calculateSliceNumber(final double fractionalPosition)
     {
         double linkLength = this.parentLink.getLength().si;
         for (int i = 0; i < this.crossSectionSlices.size() - 1; i++)
         {
             if (fractionalPosition >= this.crossSectionSlices.get(i).getRelativeLength().si / linkLength
                     && fractionalPosition <= this.crossSectionSlices.get(i + 1).getRelativeLength().si / linkLength)
             {
                 return i;
             }
         }
         return this.crossSectionSlices.size() - 2;
     }
 
     /**
      * Retrieve the lateral offset from the Link design line at the specified longitudinal position.
      * @param fractionalPosition double; fractional longitudinal position on this Lane
      * @return Length; the lateralCenterPosition at the specified longitudinal position
      */
     public final Length getLateralCenterPosition(final double fractionalPosition)
     {
         if (this.crossSectionSlices.size() == 1)
         {
             return this.getDesignLineOffsetAtBegin();
         }
         if (this.crossSectionSlices.size() == 2)
         {
             return Length.interpolate(this.getDesignLineOffsetAtBegin(), this.getDesignLineOffsetAtEnd(), fractionalPosition);
         }
         int sliceNr = calculateSliceNumber(fractionalPosition);
         return Length.interpolate(this.crossSectionSlices.get(sliceNr).getDesignLineOffset(),
                 this.crossSectionSlices.get(sliceNr + 1).getDesignLineOffset(), fractionalPosition
                         - this.crossSectionSlices.get(sliceNr).getRelativeLength().si / this.parentLink.getLength().si);
     }
 
     /**
      * Retrieve the lateral offset from the Link design line at the specified longitudinal position.
      * @param longitudinalPosition Length; the longitudinal position on this Lane
      * @return Length; the lateralCenterPosition at the specified longitudinal position
      */
     public final Length getLateralCenterPosition(final Length longitudinalPosition)
     {
         return getLateralCenterPosition(longitudinalPosition.getSI() / getLength().getSI());
     }
 
     /**
      * Return the width of this CrossSectionElement at a specified longitudinal position.
      * @param longitudinalPosition Length; the longitudinal position
      * @return Length; the width of this CrossSectionElement at the specified longitudinal position.
      */
     public final Length getWidth(final Length longitudinalPosition)
     {
         return getWidth(longitudinalPosition.getSI() / getLength().getSI());
     }
 
     /**
      * Return the width of this CrossSectionElement at a specified fractional longitudinal position.
      * @param fractionalPosition double; the fractional longitudinal position
      * @return Length; the width of this CrossSectionElement at the specified fractional longitudinal position.
      */
     public final Length getWidth(final double fractionalPosition)
     {
         if (this.crossSectionSlices.size() == 1)
         {
             return this.getBeginWidth();
         }
         if (this.crossSectionSlices.size() == 2)
         {
             return Length.interpolate(this.getBeginWidth(), this.getEndWidth(), fractionalPosition);
         }
         int sliceNr = calculateSliceNumber(fractionalPosition);
         return Length.interpolate(this.crossSectionSlices.get(sliceNr).getWidth(),
                 this.crossSectionSlices.get(sliceNr + 1).getWidth(), fractionalPosition
                         - this.crossSectionSlices.get(sliceNr).getRelativeLength().si / this.parentLink.getLength().si);
     }
 
     /**
      * Return the length of this CrossSectionElement as measured along the design line (which equals the center line).
      * @return Length; the length of this CrossSectionElement
      */
     public final Length getLength()
     {
         return this.length;
     }
 
     /**
      * Retrieve the offset from the design line at the begin of the parent link.
      * @return Length; the offset of this CrossSectionElement at the begin of the parent link
      */
     public final Length getDesignLineOffsetAtBegin()
     {
         return this.crossSectionSlices.get(0).getDesignLineOffset();
     }
 
     /**
      * Retrieve the offset from the design line at the end of the parent link.
      * @return Length; the offset of this CrossSectionElement at the end of the parent link
      */
     public final Length getDesignLineOffsetAtEnd()
     {
         return this.crossSectionSlices.get(this.crossSectionSlices.size() - 1).getDesignLineOffset();
     }
 
     /**
      * Retrieve the width at the begin of the parent link.
      * @return Length; the width of this CrossSectionElement at the begin of the parent link
      */
     public final Length getBeginWidth()
     {
         return this.crossSectionSlices.get(0).getWidth();
     }
 
     /**
      * Retrieve the width at the end of the parent link.
      * @return Length; the width of this CrossSectionElement at the end of the parent link
      */
     public final Length getEndWidth()
     {
         return this.crossSectionSlices.get(this.crossSectionSlices.size() - 1).getWidth();
     }
 
     /**
      * Retrieve the Z offset (used to determine what covers what when drawing).
      * @return double; the Z-offset for drawing (what's on top, what's underneath).
      */
     @Override
     public double getZ()
     {
         // default implementation returns 0.0 in case of a null location or a 2D location
         return Try.assign(() -> Locatable.super.getZ(), "Remote exception on calling getZ()");
     }
 
     /**
      * Retrieve the center line of this CrossSectionElement.
      * @return OtsLine3d; the center line of this CrossSectionElement
      */
     public final OtsLine3d getCenterLine()
     {
         return this.centerLine;
     }
 
     /**
      * Retrieve the contour of this CrossSectionElement.
      * @return OtsShape; the contour of this CrossSectionElement
      */
     public final OtsShape getContour()
     {
         return this.contour;
     }
 
     /**
      * Retrieve the id of this CrossSectionElement.
      * @return String; the id of this CrossSectionElement
      */
     @Override
     public final String getId()
     {
         return this.id;
     }
 
     /**
      * Retrieve the id of this CrossSectionElement.
      * @return String; the id of this CrossSectionElement
      */
     public final String getFullId()
     {
         return getParentLink().getId() + "." + this.id;
     }
 
     /**
      * Return the lateral offset from the design line of the parent Link of the Left or Right boundary of this
      * CrossSectionElement at the specified fractional longitudinal position.
      * @param lateralDirection LateralDirectionality; LEFT, or RIGHT
      * @param fractionalLongitudinalPosition double; ranges from 0.0 (begin of parentLink) to 1.0 (end of parentLink)
      * @return Length
      */
     public final Length getLateralBoundaryPosition(final LateralDirectionality lateralDirection,
             final double fractionalLongitudinalPosition)
     {
         Length designLineOffset;
         Length halfWidth;
         if (this.crossSectionSlices.size() <= 2)
         {
             designLineOffset = Length.interpolate(getDesignLineOffsetAtBegin(), getDesignLineOffsetAtEnd(),
                     fractionalLongitudinalPosition);
             halfWidth = Length.interpolate(getBeginWidth(), getEndWidth(), fractionalLongitudinalPosition).times(0.5);
         }
         else
         {
             int sliceNr = calculateSliceNumber(fractionalLongitudinalPosition);
             double startFractionalPosition =
                     this.crossSectionSlices.get(sliceNr).getRelativeLength().si / this.parentLink.getLength().si;
             designLineOffset = Length.interpolate(this.crossSectionSlices.get(sliceNr).getDesignLineOffset(),
                     this.crossSectionSlices.get(sliceNr + 1).getDesignLineOffset(),
                     fractionalLongitudinalPosition - startFractionalPosition);
             halfWidth = Length.interpolate(this.crossSectionSlices.get(sliceNr).getWidth(),
                     this.crossSectionSlices.get(sliceNr + 1).getWidth(),
                     fractionalLongitudinalPosition - startFractionalPosition).times(0.5);
         }
 
         switch (lateralDirection)
         {
             case LEFT:
                 return designLineOffset.minus(halfWidth);
             case RIGHT:
                 return designLineOffset.plus(halfWidth);
             default:
                 throw new Error("Bad switch on LateralDirectionality " + lateralDirection);
         }
     }
 
     /**
      * Return the lateral offset from the design line of the parent Link of the Left or Right boundary of this
      * CrossSectionElement at the specified longitudinal position.
      * @param lateralDirection LateralDirectionality; LEFT, or RIGHT
      * @param longitudinalPosition Length; the position along the length of this CrossSectionElement
      * @return Length
      */
     public final Length getLateralBoundaryPosition(final LateralDirectionality lateralDirection,
             final Length longitudinalPosition)
     {
         return getLateralBoundaryPosition(lateralDirection, longitudinalPosition.getSI() / getLength().getSI());
     }
 
     /**
      * Construct a buffer geometry by offsetting the linear geometry line with a distance and constructing a so-called "buffer"
      * around it.
      * @param cse CrossSectionElement; the cross section element to construct the contour for
      * @return OtsShape; the geometry belonging to this CrossSectionElement.
      * @throws OtsGeometryException when construction of the geometry fails
      * @throws NetworkException when the resulting contour is degenerate (cannot happen; we hope)
      */
     public static OtsShape constructContour(final CrossSectionElement cse) throws OtsGeometryException, NetworkException
     {
         OtsPoint3d[] result = null;
 
         if (cse.crossSectionSlices.size() <= 2)
         {
             OtsLine3d crossSectionDesignLine = cse.centerLine;
             OtsLine3d rightBoundary =
                     crossSectionDesignLine.offsetLine(-cse.getBeginWidth().getSI() / 2, -cse.getEndWidth().getSI() / 2);
             OtsLine3d leftBoundary =
                     crossSectionDesignLine.offsetLine(cse.getBeginWidth().getSI() / 2, cse.getEndWidth().getSI() / 2);
             result = new OtsPoint3d[rightBoundary.size() + leftBoundary.size() + 1];
             int resultIndex = 0;
             for (int index = 0; index < rightBoundary.size(); index++)
             {
                 result[resultIndex++] = rightBoundary.get(index);
             }
             for (int index = leftBoundary.size(); --index >= 0;)
             {
                 result[resultIndex++] = leftBoundary.get(index);
             }
             result[resultIndex] = rightBoundary.get(0); // close the contour
         }
         else
         {
             List<OtsPoint3d> resultList = new ArrayList<>();
             List<OtsPoint3d> rightBoundary = new ArrayList<>();
             for (int i = 0; i < cse.crossSectionSlices.size() - 1; i++)
             {
                 double plLength = cse.getParentLink().getLength().si;
                 double so = cse.crossSectionSlices.get(i).getDesignLineOffset().si;
                 double eo = cse.crossSectionSlices.get(i + 1).getDesignLineOffset().si;
                 double sw2 = cse.crossSectionSlices.get(i).getWidth().si / 2.0;
                 double ew2 = cse.crossSectionSlices.get(i + 1).getWidth().si / 2.0;
                 double sf = cse.crossSectionSlices.get(i).getRelativeLength().si / plLength;
                 double ef = cse.crossSectionSlices.get(i + 1).getRelativeLength().si / plLength;
                 OtsLine3d crossSectionDesignLine =
                         cse.getParentLink().getDesignLine().extractFractional(sf, ef).offsetLine(so, eo);
                 resultList.addAll(Arrays.asList(crossSectionDesignLine.offsetLine(-sw2, -ew2).getPoints()));
                 rightBoundary.addAll(Arrays.asList(crossSectionDesignLine.offsetLine(sw2, ew2).getPoints()));
             }
             for (int index = rightBoundary.size(); --index >= 0;)
             {
                 resultList.add(rightBoundary.get(index));
             }
             // close the contour (might not be needed)
             resultList.add(resultList.get(0));
             result = resultList.toArray(new OtsPoint3d[] {});
         }
         return OtsShape.createAndCleanOtsShape(result);
     }
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings("checkstyle:designforextension")
     public DirectedPoint getLocation()
     {
         DirectedPoint centroid = this.contour.getLocation();
         return new DirectedPoint(centroid.x, centroid.y, getZ());
     }
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings("checkstyle:designforextension")
     public Bounds getBounds()
     {
         return this.contour.getBounds();
     }
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings("checkstyle:designforextension")
     public String toString()
     {
         return String.format("CSE offset %.2fm..%.2fm, width %.2fm..%.2fm", getDesignLineOffsetAtBegin().getSI(),
                 getDesignLineOffsetAtEnd().getSI(), getBeginWidth().getSI(), getEndWidth().getSI());
     }
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings("checkstyle:designforextension")
     public int hashCode()
     {
         final int prime = 31;
         int result = 1;
         result = prime * result + ((this.id == null) ? 0 : this.id.hashCode());
         result = prime * result + ((this.parentLink == null) ? 0 : this.parentLink.hashCode());
         return result;
     }
 
     /** {@inheritDoc} */
     @Override
     @SuppressWarnings({"checkstyle:designforextension", "checkstyle:needbraces"})
     public boolean equals(final Object obj)
     {
         if (this == obj)
             return true;
         if (obj == null)
             return false;
         if (getClass() != obj.getClass())
             return false;
         CrossSectionElement other = (CrossSectionElement) obj;
         if (this.id == null)
         {
             if (other.id != null)
                 return false;
         }
         else if (!this.id.equals(other.id))
             return false;
         if (this.parentLink == null)
         {
             if (other.parentLink != null)
                 return false;
         }
         else if (!this.parentLink.equals(other.parentLink))
             return false;
         return true;
     }
 }