Collecting Raw Data with the Bad Elf App

Raw logging is a feature unique to the Bad Elf GNSS Surveyor. There are two primary purposes for this capability as listed below:

  1. To collect mixed mode NMEA/UBX files directly from the internal GPS chipset
  2. To collect binary files for later conversion into RINEX; the export format used for post-processing.

Data directly from the GNSS Surveyor includes the raw observables from the satellites it has in view. As such, one should review the best practices documents for data collection before using this feature. The most common use for this function is to create a RINEX file used for post-processing. In addition to the best practices, the following considerations are important for quality raw data collection:

  1. Ensure that the GNSS Surveyor has acquired a 3D fix
  2. Let the GNSS Surveyor acquire as many satellites as practical and ensure they have a lock (blue bars on the Bad Elf iOS app)
  3. Try to stay as far away from the GNSS Surveyor as possible to ensure it has maximum visibility of the sky
  4. For static occupations, 15 minutes of recording is generally sufficient to achieve a fixed location
  5. There is no downside to recording longer, especially in more challenging environments
  6. Recording for less than the minimum recommended time will likely only yield float solutions
  7. We recommend going to the advanced settings page and setting the elevation mask at no less than 15 degrees. Depending upon your environment you may choose to set this as high as 30 degrees.
  8. Most quality data will come from satellites that have a CNRCarrier to Noise Ratio (Signal Strength) in dBHz of greater than 30. The Bad Elf iOS app will show the CNR of each satellite. You may adjust the minimum CNR to reduce poor satellites if you desire. It's suggested that this number should be less than 30.
  9. Alternatively if you post-processing software has settings, you can leave elevation mask and CNR alone and adjust settings afterwards.

To start a raw data log, run the Bad Elf iOS app and look for the item labeled Raw Logging.

Bad Elf iOS app main UI

Selecting Raw Logging shows the following UI as depicted below.

Raw Logging UI

Starting a Raw Log

Before you start a raw log, adjust the Auto-stop setting to your preference. Using the “-” button will reduce the number of minutes for a recording. Decrementing this setting to the minimum of 5 minutes will disable the auto-stop feature. When disabled, you will need to manually turn recording on and off for the interval you choose. With auto-stop enabled, one simply needs to turn on raw logging by swiping to the right the on/off button. When the timer expires, the raw logging session is closed and you may begin another.

During active recording, a byte count is displayed below the auto-stop label. This byte count should increase steadily during the recording session.

Note: if this byte count is not incrementing it is possible you have moved too far away from the Bad Elf receiver. Restart the session as there will be an unacceptable gap in the data.

Note: the log names will automatically increment using the prefix of the last raw log name with the last digit incrementing from the previous number.

Once a raw log is completed a new entry is presented in the list below the raw logging settings. Clicking on one of these items provides a means to edit the raw log name and the associated fields used for the RINEX header. In addition, tools to offload the data are provided such that raw recordings can be stored elsewhere. For more information consult the article on offloading raw data.