Package org.apache.lucene.util

Class SloppyMath

java.lang.Object

org.apache.lucene.util.SloppyMath

public class SloppyMath
extends Object

Math functions that trade off accuracy for speed.

Constructor Summary

Constructors

Constructor	Description
SloppyMath()

Method Summary

Modifier and Type	Method	Description
static double	asin(double a)	Returns the arc sine of a value.
static double	cos(double a)	Returns the trigonometric cosine of an angle.
static double	haversinMeters(double sortKey)	Returns the Haversine distance in meters between two points given the previous result from haversinSortKey(double, double, double, double)
static double	haversinMeters(double lat1, double lon1, double lat2, double lon2)	Returns the Haversine distance in meters between two points specified in decimal degrees (latitude/longitude).
static double	haversinSortKey(double lat1, double lon1, double lat2, double lon2)	Returns a sort key for distance.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SloppyMath

public SloppyMath()

Method Detail

haversinMeters

public static double haversinMeters(double lat1,
                                    double lon1,
                                    double lat2,
                                    double lon2)

Returns the Haversine distance in meters between two points specified in decimal degrees (latitude/longitude). This works correctly even if the dateline is between the two points.

Error is at most 4E-1 (40cm) from the actual haversine distance, but is typically much smaller for reasonable distances: around 1E-5 (0.01mm) for distances less than 1000km.

Parameters:

lat1 - Latitude of the first point.

lon1 - Longitude of the first point.

lat2 - Latitude of the second point.

lon2 - Longitude of the second point.

Returns:

distance in meters.

haversinMeters

public static double haversinMeters(double sortKey)

Returns the Haversine distance in meters between two points given the previous result from haversinSortKey(double, double, double, double)

Returns:

distance in meters.

haversinSortKey

public static double haversinSortKey(double lat1,
                                     double lon1,
                                     double lat2,
                                     double lon2)

Returns a sort key for distance. This is less expensive to compute than haversinMeters(double, double, double, double), but it always compares the same. This can be converted into an actual distance with haversinMeters(double), which effectively does the second half of the computation.

cos

public static double cos(double a)

Returns the trigonometric cosine of an angle.

Error is around 1E-15.

Special cases:

• If the argument is NaN or an infinity, then the result is NaN.

Parameters:

a - an angle, in radians.

Returns:

the cosine of the argument.

See Also:

Math.cos(double)

asin

public static double asin(double a)

Returns the arc sine of a value.

The returned angle is in the range -pi/2 through pi/2. Error is around 1E-7.

Special cases:

• If the argument is NaN or its absolute value is greater than 1, then the result is NaN.

Parameters:

a - the value whose arc sine is to be returned.

Returns:

arc sine of the argument

See Also:

Math.asin(double)