Public Member Functions
void	AddEdge (double azi, double s)

void	AddPoint (double lat, double lon)

void	Clear ()

PolygonResult	Compute ()

PolygonResult	Compute (boolean reverse, boolean sign)

Pair	CurrentPoint ()

double	Flattening ()

double	MajorRadius ()

	PolygonArea (Geodesic earth, boolean polyline)

PolygonResult	TestEdge (double azi, double s, boolean reverse, boolean sign)

PolygonResult	TestPoint (double lat, double lon, boolean reverse, boolean sign)

Static Private Member Functions
static int	transit (double lon1, double lon2)

static int	transitdirect (double lon1, double lon2)

Private Attributes
double	_area0

Accumulator	_areasum

int	_crossings

Geodesic	_earth

double	_lat0

int	_mask

int	_num

boolean	_polyline

Detailed Description

Polygon areas.

This computes the area of a geodesic polygon using the method given Section 6 of

C. F. F. Karney, Algorithms for geodesics, J. Geodesy 87, 43–55 (2013) (addenda).

This class lets you add vertices one at a time to the polygon. The area and perimeter are accumulated at two times the standard floating point precision to guard against the loss of accuracy with many-sided polygons. At any point you can ask for the perimeter and area so far. There's an option to treat the points as defining a polyline instead of a polygon; in that case, only the perimeter is computed.

Example of use:

// Compute the area of a geodesic polygon.
// This program reads lines with lat, lon for each vertex of a polygon.
// At the end of input, the program prints the number of vertices,
// the perimeter of the polygon and its area (for the WGS84 ellipsoid).
import java.util.*;
import net.sf.geographiclib.*;
public class Planimeter {
  public static void main(String[] args) {
    PolygonArea p = new PolygonArea(Geodesic.WGS84, false);
    try {
      Scanner in = new Scanner(System.in);
      while (true) {
        double lat = in.nextDouble(), lon = in.nextDouble();
        p.AddPoint(lat, lon);
      }
    }
    catch (Exception e) {}
    PolygonResult r = p.Compute();
    System.out.println(r.num + " " + r.perimeter + " " + r.area);
  }
}

Definition at line 60 of file PolygonArea.java.

Constructor & Destructor Documentation

net.sf.geographiclib.PolygonArea.PolygonArea	(	Geodesic	earth,
		boolean	polyline
	)

inline

Constructor for PolygonArea.

Parameters

earth	the Geodesic object to use for geodesic calculations.
polyline	if true that treat the points as defining a polyline instead of a polygon.

Definition at line 101 of file PolygonArea.java.

Member Function Documentation

void net.sf.geographiclib.PolygonArea.AddEdge	(	double	azi,
		double	s
	)

inline

Add an edge to the polygon or polyline.

Parameters

azi	azimuth at current point (degrees).
s	distance from current point to next point (meters).

This does nothing if no points have been added yet. Use PolygonArea.CurrentPoint to determine the position of the new vertex.

Definition at line 160 of file PolygonArea.java.

void net.sf.geographiclib.PolygonArea.AddPoint	(	double	lat,
		double	lon
	)

inline

Add a point to the polygon or polyline.

Parameters

lat	the latitude of the point (degrees).
lon	the latitude of the point (degrees).

lat should be in the range [−90°, 90°].

Definition at line 134 of file PolygonArea.java.

void net.sf.geographiclib.PolygonArea.Clear ( )

inline

Clear PolygonArea, allowing a new polygon to be started.

Definition at line 118 of file PolygonArea.java.

PolygonResult net.sf.geographiclib.PolygonArea.Compute ( )

inline

Return the results so far.

Returns: PolygonResult(num, perimeter, area) where num is the number of vertices, perimeter is the perimeter of the polygon or the length of the polyline (meters), and area is the area of the polygon (meters²) or Double.NaN of polyline is true in the constructor.

Counter-clockwise traversal counts as a positive area.

Definition at line 184 of file PolygonArea.java.

PolygonResult net.sf.geographiclib.PolygonArea.Compute	(	boolean	reverse,
		boolean	sign
	)

inline

Return the results so far.

Parameters

reverse	if true then clockwise (instead of counter-clockwise) traversal counts as a positive area.
sign	if true then return a signed result for the area if the polygon is traversed in the "wrong" direction instead of returning the area for the rest of the earth.

Returns: PolygonResult(num, perimeter, area) where num is the number of vertices, perimeter is the perimeter of the polygon or the length of the polyline (meters), and area is the area of the polygon (meters²) or Double.NaN of polyline is true in the constructor.

More points can be added to the polygon after this call.

Definition at line 201 of file PolygonArea.java.

Pair net.sf.geographiclib.PolygonArea.CurrentPoint ( )

inline

Report the previous vertex added to the polygon or polyline.

Returns: Pair(lat, lon), the current latitude and longitude.

If no points have been added, then Double.NaN is returned. Otherwise, lon will be in the range [−180°, 180°].

Definition at line 390 of file PolygonArea.java.

double net.sf.geographiclib.PolygonArea.Flattening ( )

inline

Returns: f the flattening of the ellipsoid. This is the value inherited from the Geodesic object used in the constructor.

Definition at line 380 of file PolygonArea.java.

double net.sf.geographiclib.PolygonArea.MajorRadius ( )

inline

Returns: a the equatorial radius of the ellipsoid (meters). This is the value inherited from the Geodesic object used in the constructor.

Definition at line 374 of file PolygonArea.java.

PolygonResult net.sf.geographiclib.PolygonArea.TestEdge	(	double	azi,
		double	s,
		boolean	reverse,
		boolean	sign
	)

inline

Return the results assuming a tentative final test point is added via an azimuth and distance; however, the data for the test point is not saved. This lets you report a running result for the perimeter and area as the user moves the mouse cursor. Ordinary floating point arithmetic is used to accumulate the data for the test point; thus the area and perimeter returned are less accurate than if AddPoint and Compute are used.

Parameters

azi	azimuth at current point (degrees).
s	distance from current point to final test point (meters).
reverse	if true then clockwise (instead of counter-clockwise) traversal counts as a positive area.
sign	if true then return a signed result for the area if the polygon is traversed in the "wrong" direction instead of returning the area for the rest of the earth.

Returns: PolygonResult(num, perimeter, area) where num is the number of vertices, perimeter is the perimeter of the polygon or the length of the polyline (meters), and area is the area of the polygon (meters²) or Double.NaN of polyline is true in the constructor.

Definition at line 323 of file PolygonArea.java.

PolygonResult net.sf.geographiclib.PolygonArea.TestPoint	(	double	lat,
		double	lon,
		boolean	reverse,
		boolean	sign
	)

inline

Return the results assuming a tentative final test point is added; however, the data for the test point is not saved. This lets you report a running result for the perimeter and area as the user moves the mouse cursor. Ordinary floating point arithmetic is used to accumulate the data for the test point; thus the area and perimeter returned are less accurate than if AddPoint and Compute are used.

Parameters

lat	the latitude of the test point (degrees).
lon	the longitude of the test point (degrees).
reverse	if true then clockwise (instead of counter-clockwise) traversal counts as a positive area.
sign	if true then return a signed result for the area if the polygon is traversed in the "wrong" direction instead of returning the area for the rest of the earth.

Returns: PolygonResult(num, perimeter, area) where num is the number of vertices, perimeter is the perimeter of the polygon or the length of the polyline (meters), and area is the area of the polygon (meters²) or Double.NaN of polyline is true in the constructor.

lat should be in the range [−90°, 90°].

Definition at line 256 of file PolygonArea.java.

static int net.sf.geographiclib.PolygonArea.transit	(	double	lon1,
		double	lon2
	)

inlinestaticprivate

Definition at line 70 of file PolygonArea.java.

static int net.sf.geographiclib.PolygonArea.transitdirect	(	double	lon1,
		double	lon2
	)

inlinestaticprivate

Definition at line 84 of file PolygonArea.java.

Member Data Documentation

double net.sf.geographiclib.PolygonArea._area0

private

Definition at line 63 of file PolygonArea.java.

Accumulator net.sf.geographiclib.PolygonArea._areasum

private

Definition at line 68 of file PolygonArea.java.

int net.sf.geographiclib.PolygonArea._crossings

private

Definition at line 67 of file PolygonArea.java.

Geodesic net.sf.geographiclib.PolygonArea._earth

private

Definition at line 62 of file PolygonArea.java.

double net.sf.geographiclib.PolygonArea._lat0

private

Definition at line 69 of file PolygonArea.java.

int net.sf.geographiclib.PolygonArea._mask

private

Definition at line 65 of file PolygonArea.java.

int net.sf.geographiclib.PolygonArea._num

private

Definition at line 66 of file PolygonArea.java.

boolean net.sf.geographiclib.PolygonArea._polyline

private

Definition at line 64 of file PolygonArea.java.

The documentation for this class was generated from the following file:

PolygonArea.java

Public Member Functions

Static Private Member Functions

Private Attributes

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation