GPS Rally Odometer

This iPhone app is designed for various types of automobile rallies that require measurement of time, speed, and distance between segments of the rally route including stages and checkpoints.

To make sure that all initial conditions are set properly when using GPS, touch the "Reset/Pause" button and choose the "Reset, New Rally" option.

Begin computing distance, time, and speed by touching the "Start Rally" button. Alternatively, when the app has been either restarted to zero distance or paused, you may select a minute for the "Next Starting Time."

GPS inputs trace the path along the rally route. From time to time you may measure time, speed, and distance for a stage or a checkpoint. These measurements will be stored in a table and the points will be indicated on a map.

Options include subtraction of distance when you travel off course. A toggle button switches between on course (blue line) and off course (red line) travel.

Distance measurement can be set to miles or kilometers and time measurement can be set to minutes and seconds or decimal minutes. The distance may be displayed with either 2 or 3 digit precision. Make your selections in the app preferences in the iPhone Settings linked with a "sprocket" button beside the "About" button.

You may fine-tune the app's distance and time figures to the rally's official measures with the options in the Adjustments popup. Unlock to make adjustments and lock to save the changes you make and to prevent inadvertent changes.

There are two ways to adjust distance measurement. An adjustment factor between 0.800 and 1.200 can be used to synchronize distance measured by GPS to rally distance. This adjustment applies to all distance measurements shown after the adjustment has been selected. Also, you may pause or gain time on a particular stage by adding or subtracting time from the reported time on a stage.

If the app's Time of Day (T.O.D.) clock does not match the rally's official clock, you may synchronize the two clocks by making small adjustments as required.

For better GPS reception and improved accuracy while racing, third-party wireless GPS receivers are recommended. This app has been tested with Bluetooth connectivity to a Dual XGPS150A Universal GPS Receiver.

Disclaimer: Continued use of GPS running in the background can dramatically decrease battery life.


changes in version 4.6
  • Added estimate of distance travelled between GPS distance signals. This improves the accuracy of the distance measurement and importantly reduces the large incremental changes in distance and speed computations and displays
  • GUI modifications to improve readability
changes in version 4.3
  • Added option to adjust T.O.D. clock to match official rally clock, if necessary
  • Added option to display distance to either 2-digit or 3-digit precision. The option is available in the app settings
  • Changed the way you may enter time Gains or Pauses. A slider will allow you to select half-minute increments quickly and easily
changes in version 4.1
  • Added a "Next Starting Time" option that will start or resume computations at a chosen minute. A countdown clock will show the time remaining until the start
  • Added settings button shown as a sprocket to top navigation bar. The settings button is only active when the app has been reset
  • GUI changes to close popups when they are no longer needed or selections have been made
  • Altered the way the decimal minute "pauses" or "gains" are chosen and displayed
changes in version 4.0
  • Orientation has been changed from Portrait to Landscape due to customer preferences. The Landscape orientation allows larger text for improved readability and better mounting options for clipboards or dashboards
  • The CheckPoint button has been removed. If you would like, you may touch the New Stage button at a checkpoint to freeze the TSD measurements there
  • Optionally, you may Pause or Stop the TSD processing
  • When time adjustments for Pauses or Gains are made during a stage, the word "adjusted" will appear below the total time to indicate that the total time reflects these adjustments
  • The About button is disabled while the app is computing thereby eliminating the chance that the popup will appear by an accidental touch
  • The only mapping option is street level mapping since other satellite or hybrid options are often difficult to access during a rally
  • CAUTION: Background location processing with Apple's GPS receiver is problematic in iOS 10, so avoid background mode when in use. Background location processing works as expected with the Dual 150 and 160 GPS receivers, however
  • Numerous code changes and improvements
change in version 3.3
  • Location access is now always available by default even when the app is in background mode thereby improving distance measurements and route tracking. In some cases, you may have to be sure that "Always" is checked in "Settings" for this app
changes in version 3.0
  • Added support for Dual XGPS150 and XGPS160 receivers that allow sampling of GPS positional data at up to 5 and 10 times per second respectively for improved accuracy over the internal iPhone one time per second sampling
  • The Dual receivers are connected to the iPhone via Bluetooth so be sure to turn on Bluetooth even while in Airport mode for reception
  • To receive information solely from the Dual receivers, put the iPhone into Airplane mode with Bluetooth on. This will also extend the battery life of the iPhone

revised: April 16, 2017