org.transitime.utils

Class ChinaGpsOffset

java.lang.Object

org.transitime.utils.ChinaGpsOffset

public class ChinaGpsOffset
extends java.lang.Object

For dealing with the map offset issue in China. All maps have to be offset in China, a legacy from the cold war. So to properly show stops and shapes on a map, such as a Google one, for China need to offset the locations. Code is based on https://on4wp7.codeplex.com/SourceControl/changeset/view/21455# EvilTransform.cs as described at the very useful posting at http://www.sinosplice .com/life/archives/2013/07/16/a-more-complete-ios-solution -to-the-china-gps-offset-problem.

Author:

SkiBu Smith

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ChinaGpsOffset.LatLon This simple inner class created so don't depend on other existing class that is for use with db.

Constructor Summary

Constructors

Constructor and Description
ChinaGpsOffset()

Method Summary

Modifier and Type	Method and Description
static void	main(java.lang.String[] args)
static boolean	outOfChina(double lat, double lon) Returns true if the lat/lon specified is within a rectangle that very roughly describes China.
static ChinaGpsOffset.LatLon	transform(double wgLat, double wgLon) World Geodetic System ==> Mars Geodetic System.
static ChinaGpsOffset.LatLon	transformBack(double marsLat, double marsLon) Mars Geodetic System ==> World Geodetic System.

Methods inherited from class java.lang.Object

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

Constructor Detail

ChinaGpsOffset

public ChinaGpsOffset()

Method Detail

transform

public static ChinaGpsOffset.LatLon transform(double wgLat,
                                              double wgLon)

World Geodetic System ==> Mars Geodetic System. For transforming between a regular latitude/longitude to values that can be used with a map API so that the datapoints will be displayed in the correct place on the maps.

Parameters:

wgLat -

wgLon -

Returns:

transformBack

public static ChinaGpsOffset.LatLon transformBack(double marsLat,
                                                  double marsLon)

Mars Geodetic System ==> World Geodetic System. Don't have an exact formula but the transformation is known to be pretty consistent and not vary that much over the roughly 500m difference that the transformation causes. Therefore simply determines for the lat/lon in Mars coordinates what the offset is for that location and then subtracts that offset. This provides a good initial result, but where the fifth digit of a lat/lon is still off by one. So now that we have a better idea of the location the geodetic==>mars offset is determined for this new location, new slightly more accurate offsets are determined, and the geodetic location is determined again. The second iteration results found to usually be accurate to about 7 decimal places but for a significant number of locations the 6th digit would change and for some positions the offset would continue to creep, which is undesirable. Therefore do one last iteration. After the third iteration very few locations offset the 6th digit and there is no creep, which is great.

Parameters:

marsLat -

marsLon -

Returns:

outOfChina

public static boolean outOfChina(double lat,
                                 double lon)

Returns true if the lat/lon specified is within a rectangle that very roughly describes China. Note that this will include locations in parts of other adjacent countries that do not use the Mars mapping!

Parameters:

lat -

lon -

Returns:

main

public static void main(java.lang.String[] args)