## Calculating the Bearing/Direction to Har Habayis Using the Zmanim API

An earlier “Bearing to Yerushalayim and Zmanim Map” post demonstrated the use of JavaScript to render the bearing to Har Habayis on a Google Map. A more detailed follow-up post “Technical Information about the Bearing to Yerushalayim Map” dealt with detailed technical information on these calculations. The main Bearing to Yerushalayim and Zmanim Map page usually has the most up to date information on the subject. What was not detailed in previously published posts and pages was that most of the calculations available via JavaScript are now in the core Zmanim API. Available since the July, 2008 beta 2 release of version 1.1 is the ability to bearings/directions using both the great circle and rhumb line methods in Java. The GeoLocation Object was modified to calculate the great circle bearings (both initial and final), and rhumb line bearing from any GeoLocation Object to another. In addition, distance calculation between the two points using both of these line types is supported. What was not ported from the JavaScript version was the less accurate Haversine formula, or the simpler spherical law of cosines algorithms that yield identical results. Instead, the Zmanim API uses the far more accurate Vincenty formulae using the WGS84 geoid model of the earth. Published by the geodesist/mathematician Thaddeus Vincenty, it is said to be accurate to about one-half millimeter, more than adequate for our calculation. The code in the API is a Java port of the previously published, slightly modified version of Chris Veness’s JavaScript implementation . Below is a simple Java example of generating bearing and distances.

/**
* This program demonstrates how to calculate bearing to Yerushalayim
* using the kosherjava.com Zmanim API. Both the great circle and
* rhumb line method are shown
* To compile, ensure that the Zmanim Jar is in your classpath.
*/
import com.kosherjava.zmanim.util.GeoLocation;
import java.util.TimeZone;

public class BearingToYerushalayim{
public static void main(String [] args) {
GeoLocation lakewood = new GeoLocation("Lakewood, NJ", 40.09596, -74.22213, 0, TimeZone.getTimeZone("America/New_York"));
GeoLocation harHabayis = new GeoLocation("Har Habayis", 31.77805, 35.235149, 0, TimeZone.getTimeZone("Asia/Jerusalem"));

double greatCircleInitialBearing = lakewood.getGeodesicInitialBearing(harHabayis);
double greatCircleDistance = lakewood.getGeodesicDistance(harHabayis);

double rhumbLineBearing = lakewood.getRhumbLineBearing(harHabayis);
double rhumbLineDistance = lakewood.getRhumbLineDistance(harHabayis);

System.out.println("Great circle initial bearing: " + greatCircleInitialBearing + " degrees ");
System.out.println("Great circle distance: " + greatCircleDistance / 1000 + " km");

System.out.println("Rhumb line bearing: " + rhumbLineBearing + " degrees");
System.out.println("Rhumb line distance: " + rhumbLineDistance / 1000 + " km");

}
}


## Question:

Where is the main method?

This is a more technical variant of the “How do I install the Zmanim API Program?”, but coming from someone who already knows that it is a Java program that can’t be installed, but assumes that it can be run. The main method is the entry point to a Java program. Since this is a library/API and not a program, it does not have a main method. The code to generate zmanim is spelled out in the How to Use the Zmanim API page. Below is a full example of a very simple zmanim program that outputs sunrise, sof zman krias shema and sunset for the current day in Lakewood, NJ. Please ensure that the Zmanim jar (download) is in your classpath.

/**
* This program is a simple demonstration of the kosherjava.com Zmanim API.
* To compile, ensure that the Zmanim Jar is in your classpath.
*/
import com.kosherjava.zmanim.*;
import com.kosherjava.zmanim.util.*;
import java.util.TimeZone;
public class SimpleZmanim{
public static void main(String [] args) {
String locationName = "Lakewood, NJ";
double latitude = 40.096; //latitude of Lakewood, NJ
double longitude = -74.222; //longitude of Lakewood, NJ
double elevation = 0; //optional elevation
//use a Valid Olson Database timezone listed in java.util.TimeZone.getAvailableIDs()
TimeZone timeZone = TimeZone.getTimeZone("America/New_York");
//create the location object
GeoLocation location = new GeoLocation(locationName, latitude, longitude, elevation, timeZone);
//create the ZmanimCalendar
ZmanimCalendar zc = new ZmanimCalendar(location);
//optionally set the internal calendar. If not set it will default to the current date
//zc.getCalendar().set(1969, Calendar.FEBRUARY, 8);
System.out.println("Today's Zmanim for " + locationName);
System.out.println("Sunrise: " + zc.getSunrise()); //output sunrise
System.out.println("Sof Zman Shema GRA: " + zc.getSofZmanShmaGRA()); //output Sof Zman Shema GRA
System.out.println("Sunset: " + zc.getSunset()); //output sunset
}
}


The following would compile and execute this code (sample from a DOS prompt in Windows).

C:\path\to\code>javac SimpleZmanim.java

C:\path\to\code>java SimpleZmanim

Today's Zmanim for Lakewood, NJ
Sunrise: Thu Nov 05 06:30:27 EST 2009
Sof Zman Shema GRA: Thu Nov 05 09:05:21 EST 2009
Sunset: Thu Nov 05 16:50:02 EST 2009


Please see the Zmanim API documentation for a more complete view of the API.