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Positioning Application: Why does PosApp (SimGEN) round the data provided by user-defined motion?


The question is mainly related to observations being made between the number of decimal places used by the users input vehicle motion and PosApp's vehicle output data (quick-look / bulk logging / datastreaming) and will be of direct interest to users with the SimGEN mode of PosApp; where vehicle motion can be defined in ECEF or geodetic coordinates, either by preparing a .umt file of the data or by sending the motion in real-time from a remote system. However the information below may well be of interest to all PosApp users.

SimGEN users may define their own motion with parameters specified to their own choice of precision (how many decimal places the parameter is given). PosApp will read in that data as a long float, which effectively means it is read as a double --> 8-byte storage == 15 digit precision. If the customer data is specified beyond the limits of this number size then any precision which exceeds that will be ignored.

But when PosApp displays or logs the parameter that was used it does so to a fixed number of decimal place precision - which is deemed to provide a more than sufficient enough level of accuracy (in the data output) for that particular parameter. So, taking vehicle ECEF X-Y-Z position data as an example:-

  • Bulk log motion data uses up to 4 decimal places
  • Bulk log aiding data uses up to 7 decimal places
  • Quick-look data uses up to 4 decimal places
  • Datastreaming uses up to 3 decimal places

Hence it should not be assumed that just because the PosApp data output is maybe presented to a lower number of decimal places than the input motion, that the full precision of the input motion was not used.

Product : SimGEN,PosApp