GeoTime software can be used for the following.

  • Convert Latitude-Longitude to UTM, in WGS-84.
  • Convert UTM to Latitude-Longitude, in WGS-84.
  • Interactively pick locations on map to determine the Latitude/Longitude and UTM of that point, and vice versa.
  • Compute the Julian Day for any date-time value.
  • Compute the Sidereal Time for the current location picked.
  • Compute the Sunrise and Sunset times for the current location picked.
  • Compute the exact times for Solstice and Equinox for any year.
  • Show plots of Earth-Sun Analemma for the selected location.
  • Conversions of date to the Islamic and Hebrew calendars.
  • Compute the current time on Mars

Additionally, it can convert from WGS-84 to some other datum's. In it's presence form, these conversion are for some countries I am familiar with and include Malaysia, Thailand and Australia, but other datum's can be easily added upon request. There is also provision for Borneo Rectified Skewed Orthomorphic (BRSO) when using the Timbalai datum.

GeoTimeConverter is a 32/64 bit application for Windows 10, and is available on the Windows Store at this link



The date and time is selected in the "local time" of the location that has been previously selected. Several methods are available for selecting values of date and time, include:

  • Select a value from the drop-down calendar.
  • Using the up and down arrows.
  • Entering values of date and time directly to the Y/M/D and H/M/S text boxes.
  • Clicking on the Current Time or UTC 00:00 buttons

If a different location is later selected, then the local time is converted to a new value by assuming UTC time is unchanged.

The three tabs labeled "Local Time", Sunrise-Sunset" and "Other Calendars" show additional time and date computations. The sunrise and sunset times are referenced to the local Daylight Savings Time, should that be applicable. Noting that the sunrise/sunset plots, by default, are not referenced to DST times. The conversions to the Hebrew and Islamic calendars can be found under the Other Calendars tab. If the page is expanded in size, the information from the tabs will be shown all together.


More details on selecting a location

The map displayed is from the Microsoft Bing Maps API. An internet connection is required to view the map.

To select a location from the Map, simply double click at the desired location.

If the Latitude and/or Longitude values are manually updated, the convert button will need to be clicked. After clicking this button, the UTM's are re-computed and the Map location updated. The convert button will turn green as the data is being entered, indicating that it will need to pressed. Similarly when updated the UTM values.

The Time Zone for a location is also determined for each location. The  "time-of-day" of the computed and the data is internally referenced to UTC time, so when the time zone is changed, the UTC time will remain unchanged and  the local time will get updated. There are 3 methods of determining the time zone.

The first time zone method is to use the PC clock. This method is probably only useful when you are selecting locations that are nearby to and in your local time zone.

The second and default method is to determine the time zone from the selected location, which returns the time zone value for either standard time or summer time (DST) depending on the time of the year. The input information are the latitude and longitude of the selected location. If a location is selected over the ocean, a time zone value computed from a 15 deg segment of longitude is returned. 

The third time zone method is to set the time zone value manually. This method would be used when there is no active internet connect, or in the rare case when the method 2 doesn't give a correct value.

Up to 10 sets of location data can be saved to the local computer, which will be automatically re-loaded when the app is next restarted. To save a current location setting, click on an empty cell, then select the Save button. If a cell already contains data, it will be over written. To restoring data from a cell, click on the cell to be restored, then select the Restore button.


Sunrise, Sunset and Analemma plots.

These plots can be accessed by clicking on the second button under the hamburger icon on the far left. By default, they are both displayed using local time that does not have any Daylight Saving Time corrections applied (if DST is applicable to the selected location). Since the sunrise and sunset times display on the main map screen are corrected to Daylight Savings Time, then there may be a hour offset between the two at some times of the year. To plot the data with Daylight Savings Time, then click on the check box at the bottom of the page.



Keys for the Bing Maps API

The map displayed is from the Microsoft Bing Maps API. This API requires an active internet connection, so if no internet connection is available then the map does not display or update. Additionally, an API key is required for it to function and a  key is embedded in the software.

It is possible that at some time in the future, the Bing Maps API key that is embedded in the software will cease to work, either due to expiration or over-use. You will see a message on the map saying "Invalid Credentials. Sign up for a developer account".

In that situation, you can obtain your own key from  https://msdn.microsoft.com/en-us/library/ff428642.aspx and load it from the option under the Tools menu. Use your regular Microsoft username and password.

This new personal key may become disconnected from GeoTime software when you re-install or update GeoTime, so will need to be entered again.

As far as I know, for fairly limited use, the Bing Maps key is free use up to a certain number of daily transactions (which is quite high), even though it is called a "billable key".  Although I dont believe there is any extra cost associated with getting a Bing Maps API key for low level usage, but if there is any extra cost, then this is extra and above any cost that may have been paid to acquire theGeoTimeConverter app.

When obtaining a key, select Key Type=Basic and Application Type=Public Windows App (8.x and earlier). The Application Name is GeoTimeConverter.





  1. Astronomical Algorithms, 2nd Edition. Jean Meeus.


Version History


Version 2.0.15

04-Oct-2017. Added sunrise and sunset plots. Added Analemma plots. Added conversions of date to the Hebrew and Islamic calendars.


Version 2.0.11

19-Sep-2017. Added some datum conversion options. Preliminary implementation that only included datum's from Australia, Malaysia and Thailand.


Version 2.0.9

12-Sep-2017. First release




 Privacy Policy

Link to Windows Store Privacy Policy for GeoTime, that is required for Windows Store Apps.