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With OTF on and computation on an ellipsoid, the coordinates were transformed twice(!) when measuring perimeter.
124 lines
4.1 KiB
Plaintext
124 lines
4.1 KiB
Plaintext
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class QgsDistanceArea
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{
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%TypeHeaderCode
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#include <qgsdistancearea.h>
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%End
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public:
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//! Constructor
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QgsDistanceArea();
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//! Destructor
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~QgsDistanceArea();
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//! Copy constructor
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QgsDistanceArea( const QgsDistanceArea &origDA );
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//! sets whether coordinates must be projected to ellipsoid before measuring
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void setEllipsoidalMode( bool flag );
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//! returns projections enabled flag
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bool ellipsoidalEnabled() const;
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//! sets source spatial reference system (by QGIS CRS)
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void setSourceCrs( long srsid );
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/**
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* Sets source spatial reference system (by QGIS CRS)
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* @note: missing in Python bindings in QGIS < 2.2
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*/
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void setSourceCrs( const QgsCoordinateReferenceSystem& srcCRS );
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//! sets source spatial reference system by authid
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void setSourceAuthId( QString authid );
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//! returns source spatial reference system
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long sourceCrs() const;
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//! What sort of coordinate system is being used?
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bool geographic() const;
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//! sets ellipsoid by its acronym
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bool setEllipsoid( const QString& ellipsoid );
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//! Sets ellipsoid by supplied radii
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// Inverse flattening is calculated with invf = a/(a-b)
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bool setEllipsoid( double semiMajor, double semiMinor );
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//! returns ellipsoid's acronym
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const QString& ellipsoid() const;
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//! returns ellipsoid's semi major axis
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double ellipsoidSemiMajor() const;
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//! returns ellipsoid's semi minor axis
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double ellipsoidSemiMinor() const;
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//! returns ellipsoid's inverse flattening
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double ellipsoidInverseFlattening() const;
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//! general measurement (line distance or polygon area)
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double measure( QgsGeometry* geometry );
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//! measures perimeter of polygon
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double measurePerimeter( QgsGeometry* geometry );
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//! measures line
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double measureLine( const QList<QgsPoint>& points );
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//! measures line with one segment
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double measureLine( const QgsPoint& p1, const QgsPoint& p2 );
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//! measures polygon area
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double measurePolygon( const QList<QgsPoint>& points );
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//! compute bearing - in radians
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double bearing( const QgsPoint& p1, const QgsPoint& p2 );
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static QString textUnit( double value, int decimals, QGis::UnitType u, bool isArea, bool keepBaseUnit = false );
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//! Helper for conversion between physical units
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void convertMeasurement( double &measure /In,Out/, QGis::UnitType &measureUnits /In,Out/, QGis::UnitType displayUnits, bool isArea );
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protected:
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//! measures line distance, line points are extracted from WKB
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// @note available in python bindings
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// const unsigned char* measureLine( const unsigned char* feature, double* area, bool hasZptr = false );
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//! measures polygon area and perimeter, vertices are extracted from WKB
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// @note available in python bindings
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// const unsigned char* measurePolygon( const unsigned char* feature, double* area, double* perimeter, bool hasZptr = false );
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/**
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calculates distance from two points on ellipsoid
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based on inverse Vincenty's formulae
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Points p1 and p2 are expected to be in degrees and in currently used ellipsoid
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@note if course1 is not NULL, bearing (in radians) from first point is calculated
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(the same for course2)
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@return distance in meters
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*/
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double computeDistanceBearing( const QgsPoint& p1, const QgsPoint& p2,
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double* course1 = NULL, double* course2 = NULL );
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//! uses flat / planimetric / Euclidean distance
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double computeDistanceFlat( const QgsPoint& p1, const QgsPoint& p2 );
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//! calculate distance with given coordinates (does not do a transform anymore)
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double computeDistance( const QList<QgsPoint>& points );
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/**
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calculates area of polygon on ellipsoid
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algorithm has been taken from GRASS: gis/area_poly1.c
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*/
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double computePolygonArea( const QList<QgsPoint>& points );
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double computePolygonFlatArea( const QList<QgsPoint>& points );
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/**
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precalculates some values
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(must be called always when changing ellipsoid)
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*/
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void computeAreaInit();
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};
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