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If I provide my own, user-defined motion to PosApp with only position and/or velocity data, is there a way for PosApp to automatically add the higher rate terms?


Under normal circumstances, if you load PosApp with a "User Motion File" (.umt file) or send remote motion commands from a remote system, and the motion only contains position then PosApp will conclude that velocity is intended to be zero and the vehicle will be moved from one position to the next as if it is an instantaneous 'jump', i.e. no rate of change of position over the time step. Equally, if the motion only contains position and velocity PosApp will conclude that acceleration. And so forth. Any large or unexpected changes in the vehicle dynamic can thus lead to position, velocity or scaling errors (see article SOL10218 for a description of these types of messages).

Users who have the SimGEN mode of PosApp and use a .umt file can insert "INTERP" commands in the opening line of the file (see the SimGEN user manual, DGP00686AAA, for more information on the INTERP commands) to instruct PosApp to interpolate for higher rate terms based on the content of the file, e.g. interpolate velocity and acceleration from the position data in the file.

But all users can also make use of the Check Motion Utility – installed with PosApp - to analyse the motion BEFORE it is sent to PosApp and generate a new file with the additional higher rate terms included. The utility can be found in the PosApp directory and there is also a user manual, DGP01045AAA, provided in the ‘Docs’ folder which will explain in further detail the purpose of the utility.

If you normally send motion via remote commands then you will first need to capture the motion into a file in order to load it with the Check Motion Utility. The motion file must be in Spirent's MOT or MOTB formats (see the SimREMOTE manual, DGP00792AA, for a definition of those formats) or use one of the NMEA message formats that provide time and position information, e.g. GGA, GLL or RMC. A .umt file will already use one of these formats.

The utility can be used to generate 'other' motion parameters based on the data in your motion file. You must tick those parameters that you want the utility to calculate for you. So, for example, if you have a file with only position and velocity data then you might choose to tick "acceleration" and "jerk" and the utility will use your position and velocity data to interpolate those higher rate terms. Another approach might be that your motion includes position, velocity, acceleration and jerk but you want the utility to recalculate the parameters you tick based on the other data in your file, e.g. you 'trust' your acceleration data is correct but are uncertain about your position and velocity data, so you would just tick "Position" and "Velocity".

The utility provides some output files, one of which, "CheckMotion_interp.umt", is the new ‘interpolated’ motion file (the other files are a summary of any motion errors that it finds). Where there were significant errors with the original motion file the interpolated file may have missing timestamped data. This is OK because when the motion file is run with PosApp again PosApp's own motion extrapolation algorithm will ensure the vehicle moves in a 'smooth' trajectory through those epochs that have missing timestamped motion data.


  1. The utility allows you to add personality limits which further enhances the dynamic control that you may want the utility to impose when it performs its analysis of the original input motion file.
  2. The 'quality' of the interpolated data will be greatly influenced by the original motion data that was used. For example, if only using position data to interpolate for velocity, acceleration and jerk then the magnitude of the interpolated parameters is likely to be greater than if you use velocity (or position and velocity) data to interpolate for acceleration and jerk.
  3. The utility output file is in either MOT or MOTB format which is only compatible for use with the SimGEN mode of PosApp. SimREPLAYplus users who wish to create a new scenario using the output file must raise a special scenario request by logging in to the support website, including a suitable note about providing a motion file in the 'Comments' field at the end of the form and then sending the required motion file to, quoting the name of the special scenario request accordingly. Article FAQ11226 describes the different scenario request options.

Product : Check Motion,SimREPLAYplus,SimGEN,PosApp