Calculate the great-circle distance between two coordinates on a sphere. More...

#include <geospatial.h>

Inheritance diagram for Xapian::GreatCircleMetric:

Public Member Functions
	GreatCircleMetric ()
	Construct a GreatCircleMetric.

	GreatCircleMetric (double radius_)
	Construct a GreatCircleMetric using a specified radius.

double	pointwise_distance (const LatLongCoord &a, const LatLongCoord &b) const
	Return the great-circle distance between points on the sphere.

LatLongMetric *	clone () const
	Clone the metric.

std::string	name () const
	Return the full name of the metric.

std::string	serialise () const
	Serialise object parameters into a string.

LatLongMetric *	unserialise (const std::string &serialised) const
	Create object given string serialisation returned by serialise().

Public Member Functions inherited from Xapian::LatLongMetric
virtual	~LatLongMetric ()
	Destructor.

double	operator() (const LatLongCoords &a, const LatLongCoords &b) const
	Return the distance between two coordinate lists, in metres.

double	operator() (const LatLongCoords &a, const std::string &b) const
	Return the distance between two coordinate lists, in metres.

double	operator() (const LatLongCoords &a, const char *b_ptr, size_t b_len) const
	Return the distance between two coordinate lists, in metres.

Detailed Description

Calculate the great-circle distance between two coordinates on a sphere.

Experimental - see https://xapian.org/docs/deprecation#experimental-features

This uses the haversine formula to calculate the distance. Note that this formula is subject to inaccuracy due to numerical errors for coordinates on the opposite side of the sphere.

See https://en.wikipedia.org/wiki/Haversine_formula

Constructor & Destructor Documentation

◆ GreatCircleMetric() [1/2]

Xapian::GreatCircleMetric::GreatCircleMetric ( )

Construct a GreatCircleMetric.

The (quadratic mean) radius of the Earth will be used by this calculator.

◆ GreatCircleMetric() [2/2]

Xapian::GreatCircleMetric::GreatCircleMetric ( double radius_ )

explicit

Construct a GreatCircleMetric using a specified radius.

This is useful for data sets in which the points are not on Earth (eg, a database of features on Mars).

Parameters

radius_ The radius of the sphere to use, in metres.

Member Function Documentation

◆ clone()

LatLongMetric * Xapian::GreatCircleMetric::clone ( ) const

virtual

Clone the metric.

Implements Xapian::LatLongMetric.

◆ name()

std::string Xapian::GreatCircleMetric::name ( ) const

virtual

Return the full name of the metric.

This is used when serialising and unserialising metrics; for example, for performing remote searches.

If the subclass is in a C++ namespace, the namespace should be included in the name, using "::" as a separator. For example, for a LatLongMetric subclass called "FooLatLongMetric" in the "Xapian" namespace the result of this call should be "Xapian::FooLatLongMetric".

Implements Xapian::LatLongMetric.