Galactic Guardian: Zap GPS

Galactic Guardian is an Arcade/Action game for the Android cell phone. It was originally submitted as a contestant in the Android Developer Challenge 2. It is now available in a Lite version with reduced features.
The game description on the Android Market is:
The Guardian Patrol, at the request of the Galactic Federation, placed Earth under surveillance. They deployed numerous satellites to accomplish this. 
Android phones can track, target and fire on the Guardian Patrol Sentinels (GPS) to damage them. All Android phone owners are called upon to combat this privacy invasion.
The information provided with the game expands the story and provides directions. A blog entry addresses the release (and provides a place for comments).
Galactic Guardian: Zap GPS is an augmented reality game using the sensors and GPS capabilities of the Android. The best method of play is performed by aiming, like a camera, the Android at a GPS (Guardian Patrol Sentinel) satellite. Real-time Global Positioning System satellite information is used for positioning the Sentinels. The game is physical, requiring the player to turn through 360 degrees to attain the proper azimuth (compass bearing) and raising the Android overhead to attain the proper elevation. When positioned correctly the image of a Sentinel appears in the cross-hairs. The Sentinel is fired upon by pressing the camera button or the keypad (trackball) center button. The Android vibrates when fired and the targeting circle turns red. If the user is successful in targetting a Sentinel, the Android vibrates from the "shockwave" and the screen flashes from the destruction of the Sentinel.

When a Sentinel is damaged it is removed from a target list. When all Sentinels are gone the Galactic Patrol replaces them, usually with more robust versions, and the game starts again. New Sentinels may be shielded, under "command and control", or cloaked.
  • Shielding - increased shielding requires more concentrated power on the Sentinel. The energy beam is smaller and the targeting cross-hairs show this by reducing in size. 
  • Command and Control - Sentinels are coordinated so they must be destroyed in order of increasing Sentinel number. This is a challenge when the signal for the real GPS satellite is marginal. If the Android stops receiving the signal it is removed from the list. If the player is targeting that entry it disappears and a new Sentinel is now first on the list. The player most move to acquire the new Sentinel. But a marginal signal may improve, suddenly putting the original Sentinel back as first on the list. 
  • Cloaking - Sentinels may be invsibile but still present on the target list since their signal is being received. Cloaking can fade in and out. This is based, again, on the signal received from the actual GPS satellite. Below a certain level the Sentinel is cloaked and above it, visible. With luck or skill the player can target and hit the Sentinel by using the azimuth and elevation information on the display. This is only available in the paid version.
These three Sentinel capabilities are combined during various games so the challenge continuously changes. Dealing with Cloaking and Command and Control is really interesting.
A player may wish to use Galactic Guardian in a location where movement is not feasible. For this situation, there is a keypad mode which moves the azimuth and elevation, disabling the use of the Android sensors.
At times, the player may be in a location where the signals from the real GPS satellites cannot be received. A training mode provides for simulation of the Sentinel positions.
The final setting allows the elevation movement to be compressed. It is awkward to target a Sentinel that is at 89 degrees of elevation since this requires putting the Android directly overhead. Elevation compression allows overhead Sentinels to be targeted using proportionally less actual elevation of the Android.

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