QContinuum Freeware

by Dana Peters

Compass for J2ME


Use your cell phone as a compass. By rotating the phone so that the sun and/or moon icons match their location in the sky, the top of the phone will indicate true north.


Any cell phone or other mobile device with J2ME (Java 2 mobile edition).


Version 4.1

Version 3.0

This older version can be useful for phones with limited memory.


Compass uses henson.midp.Float by Nikolay Klimchuk.

Change Log

 Version 4.1

Version 4.0

Version 3.0

Version 2.0


Q: How does it work?
A: Compass computes the sun and moon position using your latitude and longitude, and the time.

Q: Why do I need to select my time zone?
A: Compass knows your local time from your phone's real time clock, but astronomical computations need GTM (Greenwich Mean Time). By selecting the time zone, Compass can compute GTM from your local time.

Q: How can I find my airport code?
A: Use the World Airport Codes web site.

Q: How do I know if my phone supports J2ME?
A: Consult the phone manufacturer's web site for specifications on your phone. Or start a game on your phone, and look for a "Java Powered" splash screen.

Q: How do I load this software on my phone?
A: Here are 4 possibilities:

  1. Start your WAP browser and enter the address qcontinuum.org/compass/compass.wml
  2. Start your WAP browser and enter wap.getjar.com, select "Quick Download", enter code 12347.
  3. If you have a cable to connect the phone to your PC, then use your phone vendor's software to copy compass.jar to the phone.
  4. If your phone is Bluetooth capable and supports OBEX file transfer, you may be able to use OBEX to copy compass.jar to your phone.

Q: How does Compass translate an airport code to the associated latitude / longitude?
A: Compass contains a database of 3000 global airports. The database is stored in a very efficient manner which requires only 21K of memory. The data was derived from the Global Airport Database. See a world map of the airport database.

Q: What algorithms does Compass use to perform astronomical calculations?
A: The calculations are based on algorithms from the book "Astronomy on the Personal Computer".

Q: Thanks for the source code. Can I use it in my own application?
A: Yes, if you follow the terms of the GNU General Public License.

No Warranty

Because this software is free of charge, there is no warranty. It is provided "as is" without warranty of any kind, either expressed or implied.