Our project displays the tidal forces affecting the surface of the Earth from the differential strength of the gravity of the Moon and the Sun on the earths surface and overlaying this information over an interactive map for easy user exploration. The simulation is time dependant so users can observe how the distribution of tidal forces changes through the year as the gravity of the Moon and the Sun align and oppose aiding in the intuitive understanding of spring tides and equinox phenomena.

This project is solving the Gravity Map challenge.


User will be able to input a date and our code will determine the instantaneous location of the Sun and Moon relative to the Earth and calculate the variations in local gravity for different parts of the Earth's surface. This information will be used to create tiles from our server to generate a time dependant map of tidal forces affecting the surface of the Earth generated by the gravitational interaction of the Moon and the Sun with Earth. These tiles will be applied to a web page created with OpenStreetMap allowing the user to interactively explore the gravity variations across the world.

We achieved these goals by discovering and converting to C, Matlab scripts describing the position of the moon and Sun in ecliptic geocentric coordinates from a Julian date input, converting these into equatorial coordinates and adding an adjustment for the time of day as the equatorial coordinate system rotates around the Earth in order to create an OpenStreetMap overlay. The online map asks the c code for a tile for a particular location on the map which is provided by recalculating the gravitational forces for the latitude and longitude represented by a pixel and calculating an r-g-b colour mapping for the gravity values outputted.

This program will allow users to explore what the tidal forces effecting the surface of the Earth look like when graphically represented showing them the forces that cause tides around the world and how they change on a daily, monthly and yearly basis. Phenomena such as spring tides and the equinox can be observed by looking at the correct times of the year to see stronger or weaker deviations from average surface gravity on earth.

Project Information

License: zlib/libpng license (Zlib)

Source Code/Project URL:


demo -


  • James Murfin
  • Tristan Heaven
  • mojtaba amiri
  • James Murfin
  • Laurence Cullen
  • Jozef Friedmansky