com.conveyal.gtfs.util

Class Util

java.lang.Object

com.conveyal.gtfs.util.Util

public abstract class Util
extends Object

The methods and classes in this package should eventually be part of a shared Conveyal library.

Field Summary

Fields

Modifier and Type	Field and Description
static com.vividsolutions.jts.geom.GeometryFactory	geometryFactory
static double	METERS_PER_DEGREE_LATITUDE

Constructor Summary

Constructors

Constructor and Description
Util()

Method Summary

Modifier and Type	Method and Description
static void	ensureValidNamespace(String namespace) Ensures namespace is valid by ensuring it only has alphanumeric characters or the underscore for all characters in the string
static double	fastDistance(double lat0, double lon0, double lat1, double lon1)
static String	getCoordString(Stop stop)
static String	human(int n)
static com.vividsolutions.jts.geom.Coordinate	projectLatLonToMeters(double lat, double lon)
static String	randomIdString() Generate a random unique prefix of n lowercase letters.
static double	xMetersForLon(double latDegrees, double lonDegrees)
static double	yMetersForLat(double latDegrees)

Methods inherited from class java.lang.Object

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

Field Detail

geometryFactory

public static com.vividsolutions.jts.geom.GeometryFactory geometryFactory

METERS_PER_DEGREE_LATITUDE

public static final double METERS_PER_DEGREE_LATITUDE

See Also:

Constant Field Values

Constructor Detail

Util

public Util()

Method Detail

human

public static String human(int n)

yMetersForLat

public static double yMetersForLat(double latDegrees)

xMetersForLon

public static double xMetersForLon(double latDegrees,
                                   double lonDegrees)

projectLatLonToMeters

public static com.vividsolutions.jts.geom.Coordinate projectLatLonToMeters(double lat,
                                                                           double lon)

getCoordString

public static String getCoordString(Stop stop)

fastDistance

public static double fastDistance(double lat0,
                                  double lon0,
                                  double lat1,
                                  double lon1)

Returns:

Equirectangular approximation to distance.

randomIdString

public static String randomIdString()

Generate a random unique prefix of n lowercase letters. We can't count on sql table or schema names being case sensitive or tolerating (leading) digits. For n=10, number of possibilities is 26^10 or 1.4E14. The approximate probability of a hash collision is k^2/2H where H is the number of possible hash values and k is the number of items hashed. SHA1 is 160 bits, MD5 is 128 bits, and UUIDs are 128 bits with only 122 actually random. To reach the uniqueness of a UUID you need math.log(2**122, 26) or about 26 letters. An MD5 can be represented as 32 hex digits so we don't save much length, but we do make it entirely alphabetical. log base 2 of 26 is about 4.7, so each character represents about 4.7 bits of randomness. The question remains of whether we need globally unique IDs or just application-unique IDs. The downside of generating IDs sequentially or with little randomness is that when multiple databases are created we'll have feeds with the same IDs as older or other databases, allowing possible accidental collisions with strange failure modes.

ensureValidNamespace

public static void ensureValidNamespace(String namespace)
                                 throws InvalidNamespaceException

Ensures namespace is valid by ensuring it only has alphanumeric characters or the underscore for all characters in the string

Parameters:

namespace -

Throws:

InvalidNamespaceException