GeographicLib
1.35
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Polygon areas. More...
#include <GeographicLib/PolygonArea.hpp>
Public Member Functions | |
PolygonArea (const Geodesic &earth, bool polyline=false) throw () | |
void | Clear () throw () |
void | AddPoint (real lat, real lon) throw () |
void | AddEdge (real azi, real s) throw () |
unsigned | Compute (bool reverse, bool sign, real &perimeter, real &area) const throw () |
unsigned | TestPoint (real lat, real lon, bool reverse, bool sign, real &perimeter, real &area) const throw () |
unsigned | TestEdge (real azi, real s, bool reverse, bool sign, real &perimeter, real &area) const throw () |
Inspector functions | |
Math::real | MajorRadius () const throw () |
Math::real | Flattening () const throw () |
void | CurrentPoint (real &lat, real &lon) const throw () |
Polygon areas.
This computes the area of a polygon whose edges are geodesics using the method given in Section 6 of
This class lets you add vertices and edges one at a time to the polygon. The sequence must start with a vertex and thereafter vertices and edges can be added in any order. Any vertex after the first creates a new edge which is the ''shortest'' geodesic from the previous vertex. In some cases there may be two or many such shortest geodesics and the area is then not uniquely defined. In this case, either add an intermediate vertex or add the edge ''as'' an edge (by defining its direction and length).
The area and perimeter are accumulated in 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:
Planimeter is a command-line utility providing access to the functionality of PolygonArea.
Definition at line 55 of file PolygonArea.hpp.
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inline |
Constructor for PolygonArea.
[in] | earth | the Geodesic object to use for geodesic calculations. By default this uses the WGS84 ellipsoid. |
[in] | polyline | if true that treat the points as defining a polyline instead of a polygon (default = false). |
Definition at line 88 of file PolygonArea.hpp.
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inline |
Clear PolygonArea, allowing a new polygon to be started.
Definition at line 99 of file PolygonArea.hpp.
Referenced by main().
void GeographicLib::PolygonArea::AddPoint | ( | real | lat, |
real | lon | ||
) | |||
throw | ( | ||
) |
Add a point to the polygon or polyline.
[in] | lat | the latitude of the point (degrees). |
[in] | lon | the longitude of the point (degrees). |
lat should be in the range [−90°, 90°] and lon should be in the range [−540°, 540°).
Definition at line 16 of file PolygonArea.cpp.
References GeographicLib::Math::AngNormalize().
Referenced by main().
void GeographicLib::PolygonArea::AddEdge | ( | real | azi, |
real | s | ||
) | |||
throw | ( | ||
) |
Add an edge to the polygon or polyline.
[in] | azi | azimuth at current point (degrees). |
[in] | s | distance from current point to next point (meters). |
azi should be in the range [−540°, 540°). This does nothing if no points have been added yet. Use PolygonArea::CurrentPoint to determine the position of the new vertex.
Definition at line 34 of file PolygonArea.cpp.
unsigned GeographicLib::PolygonArea::Compute | ( | bool | reverse, |
bool | sign, | ||
real & | perimeter, | ||
real & | area | ||
) | const | ||
throw | ( | ||
) |
Return the results so far.
[in] | reverse | if true then clockwise (instead of counter-clockwise) traversal counts as a positive area. |
[in] | 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. |
[out] | perimeter | the perimeter of the polygon or length of the polyline (meters). |
[out] | area | the area of the polygon (meters2); only set if polyline is false in the constructor. |
Definition at line 49 of file PolygonArea.cpp.
Referenced by main().
unsigned GeographicLib::PolygonArea::TestPoint | ( | real | lat, |
real | lon, | ||
bool | reverse, | ||
bool | sign, | ||
real & | perimeter, | ||
real & | area | ||
) | const | ||
throw | ( | ||
) |
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 PolygonArea::AddPoint and PolygonArea::Compute are used.
[in] | lat | the latitude of the test point (degrees). |
[in] | lon | the longitude of the test point (degrees). |
[in] | reverse | if true then clockwise (instead of counter-clockwise) traversal counts as a positive area. |
[in] | 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. |
[out] | perimeter | the approximate perimeter of the polygon or length of the polyline (meters). |
[out] | area | the approximate area of the polygon (meters2); only set if polyline is false in the constructor. |
lat should be in the range [−90°, 90°] and lon should be in the range [−540°, 540°).
Definition at line 90 of file PolygonArea.cpp.
unsigned GeographicLib::PolygonArea::TestEdge | ( | real | azi, |
real | s, | ||
bool | reverse, | ||
bool | sign, | ||
real & | perimeter, | ||
real & | area | ||
) | const | ||
throw | ( | ||
) |
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 PolygonArea::AddEdge and PolygonArea::Compute are used.
[in] | azi | azimuth at current point (degrees). |
[in] | s | distance from current point to final test point (meters). |
[in] | reverse | if true then clockwise (instead of counter-clockwise) traversal counts as a positive area. |
[in] | 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. |
[out] | perimeter | the approximate perimeter of the polygon or length of the polyline (meters). |
[out] | area | the approximate area of the polygon (meters2); only set if polyline is false in the constructor. |
azi should be in the range [−540°, 540°).
Definition at line 140 of file PolygonArea.cpp.
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inline |
Definition at line 223 of file PolygonArea.hpp.
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Definition at line 229 of file PolygonArea.hpp.
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Report the previous vertex added to the polygon or polyline.
[out] | lat | the latitude of the point (degrees). |
[out] | lon | the longitude of the point (degrees). |
If no points have been added, then NaNs are returned. Otherwise, lon will be in the range [−180°, 180°).
Definition at line 240 of file PolygonArea.hpp.