java.lang.Object
- net.sf.geographiclib.PolygonArea

public class PolygonArea
extends Object

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).

Arbitrarily complex polygons are allowed. In the case self-intersecting of polygons the area is accumulated "algebraically", e.g., the areas of the 2 loops in a figure-8 polygon will partially cancel.

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);
   }
 }

Constructor Summary

Constructors
Constructor Description

PolygonArea(Geodesic earth, boolean polyline)
Constructor for PolygonArea.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`AddEdge(double azi, double s)`	Add an edge to the polygon or polyline.
`void`	`AddPoint(double lat, double lon)`	Add a point to the polygon or polyline.
`void`	`Clear()`	Clear PolygonArea, allowing a new polygon to be started.
`PolygonResult`	`Compute()`	Return the results so far.
`PolygonResult`	`Compute(boolean reverse, boolean sign)`	Return the results so far.
`Pair`	`CurrentPoint()`	Report the previous vertex added to the polygon or polyline.
`double`	`EquatorialRadius()`
`double`	`Flattening()`
`PolygonResult`	`TestEdge(double azi, double s, boolean reverse, boolean sign)`	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.
`PolygonResult`	`TestPoint(double lat, double lon, boolean reverse, boolean sign)`	Return the results assuming a tentative final test point is added; however, the data for the test point is not saved.

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - PolygonArea
```
public PolygonArea(Geodesic earth,
                   boolean polyline)
```
    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.
- Method Detail
  - Clear
```
public void Clear()
```
    Clear PolygonArea, allowing a new polygon to be started.
  - AddPoint
```
public void AddPoint(double lat,
                     double lon)
```
    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°].
  - AddEdge
```
public void AddEdge(double azi,
                    double s)
```
    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.
  - Compute
```
public PolygonResult Compute()
```
    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.
  - Compute
```
public PolygonResult Compute(boolean reverse,
                             boolean sign)
```
    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.
  - TestPoint
```
public PolygonResult TestPoint(double lat,
                               double lon,
                               boolean reverse,
                               boolean sign)
```
    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°].
  - TestEdge
```
public PolygonResult TestEdge(double azi,
                              double s,
                              boolean reverse,
                              boolean sign)
```
    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.
  - EquatorialRadius
```
public double EquatorialRadius()
```
    Returns:
    
    a the equatorial radius of the ellipsoid (meters). This is the value inherited from the Geodesic object used in the constructor.
  - Flattening
```
public double Flattening()
```
    Returns:
    
    f the flattening of the ellipsoid. This is the value inherited from the Geodesic object used in the constructor.
  - CurrentPoint
```
public Pair CurrentPoint()
```
    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°].

Class PolygonArea

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

PolygonArea

Method Detail

Clear

AddPoint

AddEdge

Compute

Compute

TestPoint

TestEdge

EquatorialRadius

Flattening

CurrentPoint