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# OGRPolygon Class Reference

`#include <ogr_geometry.h>`

Inheritance diagram for OGRPolygon:

List of all members.

## Public Member Functions
| OGRPolygon ()
virtual const char * | getGeometryName () const
virtual OGRwkbGeometryType | getGeometryType () const
virtual OGRGeometry * | clone () const
virtual void | empty ()
virtual OGRErr | transform (OGRCoordinateTransformation *poCT)
virtual void | flattenTo2D ()
virtual double | get_Area () const
virtual int | Centroid (OGRPoint *poPoint) const
virtual int | PointOnSurface (OGRPoint *poPoint) const
virtual int | WkbSize () const
virtual OGRErr | importFromWkb (unsigned char *, int=-1)
virtual OGRErr | exportToWkb (OGRwkbByteOrder, unsigned char *) const
virtual OGRErr | importFromWkt (char **)
virtual OGRErr | exportToWkt (char **ppszDstText) const
virtual int | getDimension () const
virtual void | getEnvelope (OGREnvelope *psEnvelope) const
virtual OGRBoolean | Equals (OGRGeometry *) const
virtual void | setCoordinateDimension (int nDimension)
void | addRing (OGRLinearRing *)
void | addRingDirectly (OGRLinearRing *)
OGRLinearRing * | getExteriorRing ()
int | getNumInteriorRings () const
OGRLinearRing * | getInteriorRing (int)
virtual void | closeRings ()

## Detailed Description

Concrete class representing polygons.

Note that the OpenGIS simple features polygons consist of one outer ring, and zero or more inner rings. A polygon cannot represent disconnected regions (such as multiple islands in a political body). The OGRMultiPolygon must be used for this.

## Constructor & Destructor Documentation

OGRPolygon::OGRPolygon | ( |  | ) |

Create an empty polygon.

## Member Function Documentation

const char * OGRPolygon::getGeometryName | ( |  | ) | const`[virtual]`

Fetch WKT name for geometry type.

There is no SFCOM analog to this method.

This method is the same as the C function OGR_G_GetGeometryName().

Returns:
  name used for this geometry type in well known text format. The returned pointer is to a static internal string and should not be modified or freed.

Implements OGRGeometry.

OGRwkbGeometryType OGRPolygon::getGeometryType | ( |  | ) | const`[virtual]`

Fetch geometry type.

Note that the geometry type may include the 2.5D flag. To get a 2D flattened version of the geometry type apply the wkbFlatten() macro to the return result.

This method is the same as the C function OGR_G_GetGeometryType().

Returns:
  the geometry type code.

Implements OGRGeometry.

OGRGeometry * OGRPolygon::clone | ( |  | ) | const`[virtual]`

Make a copy of this object.

This method relates to the SFCOM IGeometry::clone() method.

This method is the same as the C function OGR_G_Clone().

Returns:
  a new object instance with the same geometry, and spatial reference system as the original.

Implements OGRGeometry.

void OGRPolygon::empty | ( |  | ) | `[virtual]`

Clear geometry information. This restores the geometry to it's initial state after construction, and before assignment of actual geometry.

This method relates to the SFCOM IGeometry::Empty() method.

This method is the same as the C function OGR_G_Empty().

Implements OGRGeometry.

OGRErr OGRPolygon::transform | ( | OGRCoordinateTransformation * | poCT | ) | `[virtual]`

Apply arbitrary coordinate transformation to geometry.

This method will transform the coordinates of a geometry from their current spatial reference system to a new target spatial reference system. Normally this means reprojecting the vectors, but it could include datum shifts, and changes of units.

Note that this method does not require that the geometry already have a spatial reference system. It will be assumed that they can be treated as having the source spatial reference system of the OGRCoordinateTransformation object, and the actual SRS of the geometry will be ignored. On successful completion the output OGRSpatialReference of the OGRCoordinateTransformation will be assigned to the geometry.

This method is the same as the C function OGR_G_Transform().

Parameters:

  | poCT | the transformation to apply.

Returns:
  OGRERR_NONE on success or an error code.

Implements OGRGeometry.

void OGRPolygon::flattenTo2D | ( |  | ) | `[virtual]`

Convert geometry to strictly 2D. In a sense this converts all Z coordinates to 0.0.

This method is the same as the C function OGR_G_FlattenTo2D().

Implements OGRGeometry.

double OGRPolygon::get_Area | ( |  | ) | const`[virtual]`

Compute area of polygon.

The area is computed as the area of the outer ring less the area of all internal rings.

Returns:
  computed area.

Implements OGRSurface.

int OGRPolygon::Centroid | ( | OGRPoint * | poPoint | ) | const`[virtual]`

Compute the polygon centroid.

The centroid location is applied to the passed in OGRPoint object.

Returns:
  OGRERR_NONE on success or OGRERR_FAILURE on error.

Implements OGRSurface.

int OGRPolygon::PointOnSurface | ( | OGRPoint * | poPoint | ) | const`[virtual]`

This method relates to the SFCOM ISurface::get_PointOnSurface() method.

NOTE: Only implemented when GEOS included in build.

Parameters:

  | poPoint | point to be set with an internal point.

Returns:
  OGRERR_NONE if it succeeds or OGRERR_FAILURE otherwise.

Implements OGRSurface.

int OGRPolygon::WkbSize | ( |  | ) | const`[virtual]`

Returns size of related binary representation.

This method returns the exact number of bytes required to hold the well known binary representation of this geometry object. Its computation may be slightly expensive for complex geometries.

This method relates to the SFCOM IWks::WkbSize() method.

This method is the same as the C function OGR_G_WkbSize().

Returns:
  size of binary representation in bytes.

Implements OGRGeometry.

OGRErr OGRPolygon::importFromWkb | ( | unsigned char * | pabyData,
|  | int | nSize = `-1` |
| ) |  |  | `[virtual]`

Assign geometry from well known binary data.

The object must have already been instantiated as the correct derived type of geometry object to match the binaries type. This method is used by the OGRGeometryFactory class, but not normally called by application code.

This method relates to the SFCOM IWks::ImportFromWKB() method.

This method is the same as the C function OGR_G_ImportFromWkb().

Parameters:

  | pabyData | the binary input data.
  | nSize | the size of pabyData in bytes, or zero if not known.

Returns:
  OGRERR_NONE if all goes well, otherwise any of OGRERR_NOT_ENOUGH_DATA, OGRERR_UNSUPPORTED_GEOMETRY_TYPE, or OGRERR_CORRUPT_DATA may be returned.

Implements OGRGeometry.

OGRErr OGRPolygon::exportToWkb | ( | OGRwkbByteOrder | eByteOrder,
|  | unsigned char * | pabyData |
| ) |  |  | const`[virtual]`

Convert a geometry into well known binary format.

This method relates to the SFCOM IWks::ExportToWKB() method.

This method is the same as the C function OGR_G_ExportToWkb().

Parameters:

  | eByteOrder | One of wkbXDR or wkbNDR indicating MSB or LSB byte order respectively.
  | pabyData | a buffer into which the binary representation is written. This buffer must be at least OGRGeometry::WkbSize() byte in size.

Returns:
  Currently OGRERR_NONE is always returned.

Implements OGRGeometry.

OGRErr OGRPolygon::importFromWkt | ( | char ** | ppszInput | ) | `[virtual]`

Assign geometry from well known text data.

The object must have already been instantiated as the correct derived type of geometry object to match the text type. This method is used by the OGRGeometryFactory class, but not normally called by application code.

This method relates to the SFCOM IWks::ImportFromWKT() method.

This method is the same as the C function OGR_G_ImportFromWkt().

Parameters:

  | ppszInput | pointer to a pointer to the source text. The pointer is updated to pointer after the consumed text.

Returns:
  OGRERR_NONE if all goes well, otherwise any of OGRERR_NOT_ENOUGH_DATA, OGRERR_UNSUPPORTED_GEOMETRY_TYPE, or OGRERR_CORRUPT_DATA may be returned.

Implements OGRGeometry.

OGRErr OGRPolygon::exportToWkt | ( | char ** | ppszDstText | ) | const`[virtual]`

Convert a geometry into well known text format.

This method relates to the SFCOM IWks::ExportToWKT() method.

This method is the same as the C function OGR_G_ExportToWkt().

Parameters:

  | ppszDstText | a text buffer is allocated by the program, and assigned to the passed pointer.

Returns:
  Currently OGRERR_NONE is always returned.

Implements OGRGeometry.

int OGRPolygon::getDimension | ( |  | ) | const`[virtual]`

Get the dimension of this object.

This method corresponds to the SFCOM IGeometry::GetDimension() method. It indicates the dimension of the object, but does not indicate the dimension of the underlying space (as indicated by OGRGeometry::getCoordinateDimension()).

This method is the same as the C function OGR_G_GetDimension().

Returns:
  0 for points, 1 for lines and 2 for surfaces.

Implements OGRGeometry.

void OGRPolygon::getEnvelope | ( | OGREnvelope * | psEnvelope | ) | const`[virtual]`

Computes and returns the bounding envelope for this geometry in the passed psEnvelope structure.

This method is the same as the C function OGR_G_GetEnvelope().

Parameters:

  | psEnvelope | the structure in which to place the results.

Implements OGRGeometry.

OGRBoolean OGRPolygon::Equals | ( | OGRGeometry * | poOther | ) | const`[virtual]`

Returns two if two geometries are equivalent.

This method is the same as the C function OGR_G_Equal().

Returns:
  TRUE if equivalent or FALSE otherwise.

Implements OGRGeometry.

void OGRPolygon::setCoordinateDimension | ( | int | nDimension | ) | `[virtual]`

Set the coordinate dimension.

This method sets the explicit coordinate dimension. Setting the coordinate dimension of a geometry to 2 should zero out any existing Z values. Setting the dimension of a geometry collection will not necessarily affect the children geometries.

Parameters:

  | nNewDimension | New coordinate dimension value, either 2 or 3.

Reimplemented from OGRGeometry.

void OGRPolygon::addRing | ( | OGRLinearRing * | poNewRing | ) |

Add a ring to a polygon.

If the polygon has no external ring (it is empty) this will be used as the external ring, otherwise it is used as an internal ring. The passed OGRLinearRing remains the responsibility of the caller (an internal copy is made).

This method has no SFCOM analog.

Parameters:

  | poNewRing | ring to be added to the polygon.

void OGRPolygon::addRingDirectly | ( | OGRLinearRing * | poNewRing | ) |

Add a ring to a polygon.

If the polygon has no external ring (it is empty) this will be used as the external ring, otherwise it is used as an internal ring. Ownership of the passed ring is assumed by the OGRPolygon, but otherwise this method operates the same as OGRPolygon::AddRing().

This method has no SFCOM analog.

Parameters:

  | poNewRing | ring to be added to the polygon.

OGRLinearRing * OGRPolygon::getExteriorRing | ( |  | ) |

Fetch reference to external polygon ring.

Note that the returned ring pointer is to an internal data object of the OGRPolygon. It should not be modified or deleted by the application, and the pointer is only valid till the polygon is next modified. Use the OGRGeometry::clone() method to make a separate copy within the application.

Relates to the SFCOM IPolygon::get_ExteriorRing() method.

Returns:
  pointer to external ring. May be NULL if the OGRPolygon is empty.

int OGRPolygon::getNumInteriorRings | ( |  | ) | const

Fetch the number of internal rings.

Relates to the SFCOM IPolygon::get_NumInteriorRings() method.

Returns:
  count of internal rings, zero or more.

OGRLinearRing * OGRPolygon::getInteriorRing | ( | int | iRing | ) |

Fetch reference to indicated internal ring.

Note that the returned ring pointer is to an internal data object of the OGRPolygon. It should not be modified or deleted by the application, and the pointer is only valid till the polygon is next modified. Use the OGRGeometry::clone() method to make a separate copy within the application.

Relates to the SFCOM IPolygon::get_InternalRing() method.

Parameters:

  | iRing | internal ring index from 0 to getNumInternalRings() - 1.

Returns:
  pointer to external ring. May be NULL if the OGRPolygon is empty.

void OGRPolygon::closeRings | ( |  | ) | `[virtual]`

Force rings to be closed.

If this geometry, or any contained geometries has polygon rings that are not closed, they will be closed by adding the starting point at the end.

Reimplemented from OGRGeometry.

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

- ogr_geometry.h
- ogrpolygon.cpp

Generated for GDAL by 1.5.1.