LocatePoint Class Reference

Provides various ways of computing the actual value of a point a given length along a line. More...

Collaboration diagram for LocatePoint:

Public Member Functions
	LocatePoint (LineString line, double length)
Coordinate	getPoint ()
int	getIndex ()
	Returns the index of the segment containing the computed point. More...

Static Public Member Functions
static Coordinate	pointAlongSegment (LineSegment seg, double length)
	Computes the location of a point a given length along a LineSegment. More...
static Coordinate	pointAlongSegment (Coordinate p0, Coordinate p1, double length)
	Computes the location of a point a given length along a line segment. More...
static Coordinate	pointAlongSegmentByFraction (Coordinate p0, Coordinate p1, double frac)
	Computes the location of a point a given fraction along a line segment. More...
static Coordinate	pointAlongLine (LineString line, double length)
	Computes the Coordinate of the point a given length along a LineString. More...

Private Member Functions
void	compute (LineString line, double length)

Private Attributes
Coordinate	pt
int	index

Detailed Description

Provides various ways of computing the actual value of a point a given length along a line.

Constructor & Destructor Documentation

LocatePoint()

LocatePoint	(	LineString	line,
		double	length
	)

References LocatePoint.compute().

Referenced by LocatePoint.pointAlongLine().

  {
    compute(line, length);
  }

Member Function Documentation

compute()

void compute ( LineString  line, double  length  )

private

References Coordinate.distance(), and LocatePoint.pointAlongSegment().

Referenced by LocatePoint.LocatePoint().

  {
    // <TODO> handle negative distances (measure from opposite end of line)
    double totalLength = 0.0;
    Coordinate[] coord = line.getCoordinates();
    for (int i = 0; i < coord.length - 1; i++) {
      Coordinate p0 = coord[i];
      Coordinate p1 = coord[i+1];
      double segLen = p1.distance(p0);
      if (totalLength + segLen > length) {
        pt = pointAlongSegment(p0, p1, length - totalLength);
        index = i;
        return;
      }
      totalLength += segLen;
    }
    // distance is greater than line length
    pt = new Coordinate(coord[coord.length - 1]);
    index = coord.length;
  }

getIndex()

int getIndex

(

)

Returns the index of the segment containing the computed point.

References LocatePoint.index.

{    return index;  }

getPoint()

Coordinate getPoint

(

)

References LocatePoint.pt.

Referenced by LocatePoint.pointAlongLine().

{    return pt;  }

pointAlongLine()

static Coordinate pointAlongLine ( LineString  line, double  length  )

static

Computes the Coordinate of the point a given length along a LineString.

Parameters

line
length

Returns

the Coordinate of the desired point

References LocatePoint.getPoint(), and LocatePoint.LocatePoint().

  {
    LocatePoint loc = new LocatePoint(line, length);
    return loc.getPoint();
  }

pointAlongSegment() [1/2]

static Coordinate pointAlongSegment ( LineSegment  seg, double  length  )

static

Computes the location of a point a given length along a LineSegment.

If the length exceeds the length of the line segment the last point of the segment is returned. If the length is negative the first point of the segment is returned.

Parameters

seg	the line segment
length	the length to the desired point

Returns

the Coordinate of the desired point

Referenced by LocatePoint.compute(), and LengthSubstring.computeSubstring().

  {
    return pointAlongSegment(seg.p0, seg.p1, length);
  }

pointAlongSegment() [2/2]

static Coordinate pointAlongSegment ( Coordinate  p0, Coordinate  p1, double  length  )

static

Computes the location of a point a given length along a line segment.

If the length exceeds the length of the line segment the last point of the segment is returned. If the length is negative the first point of the segment is returned.

Parameters

p0	the first point of the line segment
p1	the last point of the line segment
length	the length to the desired point

Returns

the Coordinate of the desired point

References Coordinate.distance(), Coordinate.x, and Coordinate.y.

  {
    double segLen = p1.distance(p0);
    double frac = length / segLen;
    if (frac <= 0.0) return p0;
    if (frac >= 1.0) return p1;

    double x = (p1.x - p0.x) * frac + p0.x;
    double y = (p1.y - p0.y) * frac + p0.y;
    return new Coordinate(x, y);
  }

pointAlongSegmentByFraction()

static Coordinate pointAlongSegmentByFraction ( Coordinate  p0, Coordinate  p1, double  frac  )

static

Computes the location of a point a given fraction along a line segment.

If the fraction exceeds 1 the last point of the segment is returned. If the fraction is negative the first point of the segment is returned.

Parameters

p0	the first point of the line segment
p1	the last point of the line segment
frac	the fraction of the segment to the desired point

Returns

the Coordinate of the desired point

References Coordinate.x, and Coordinate.y.

  {
    if (frac <= 0.0) return p0;
    if (frac >= 1.0) return p1;

    double x = (p1.x - p0.x) * frac + p0.x;
    double y = (p1.y - p0.y) * frac + p0.y;
    return new Coordinate(x, y);
  }

Member Data Documentation

index

int index

private

Referenced by LocatePoint.getIndex().

pt

Coordinate pt

private

Referenced by LocatePoint.getPoint().