Files Formats for the APAS System

Online.Files Formats for the APAS System

Published on Sunday, December 15, 1996 by Gideon Ariel
Formats for the APAS SystemFiles

We have a document on our WEB site which contains the specifications for the
different file formats You can find it at:
/APAShelp/DOS/adw-56w.html

The CF/3D files are binary files. When one uses the EXPORT capabilities of
the APAS software, data is extracted from these binary files and presented
in rows/cols of ascii tables.

I hope this helps,

Jeremy Wise, Dir R&D

 

Analog .ana file

Yes indeed the total number of samples divided by the number of channels will give the number of datapoints per channel.
 
The ENVREC contains all the information about the raw channels. The conversion of A/D units to user units is performed in two steps. First there is a conversion of A/D units to volts. This involves properties of the A/D board itself such as the #bits, voltage range, gain, etc and is performed as follows:
}
   return (iVal – chanInfo.iADZeroV) * chanInfo.fAD2Volts/chanInfo.fGain;
{  
>User Units*//*AD-
float SOFTCHAN_AD::Raw2Volts(int iVal)

 

The 2nd step is to convert volts to user units which is hardware independent. The conversion of raw to user is calculated as follows:
}
    return (Raw2Volts(iVal)-chanInfo.fOff)*chanInfo.fConv;
{
>User Units*//*AD-
float SOFTCHAN_AD::Raw2User(int iVal)
 
I’m sure some of the structure of the ANA files is somewhat confusing. This is largely because the structure of the file has evolved over the last 20 some years. New capability was added while always maintaining backwards compatibility. Clearly if one were setting out today to design the structure of the file it would be done differently.
 
The other pieces of information in the ENVREC that are important for the force plates are:
 
1) at WORD offset=267 is the 1st Plate channel. It need not be that the 1st actual channel collected belongs to a force plate. It is assumed that the force plate channels are consecutive from the 1st plate channel. The order of the channels depends on whether the plate is a 6 channel plate such as AMTI in which case the order is assumed to be:

 

            Fx|Fy|Fz| Mx|My|Mz

 

If it is an 8 channel plate such as Kistler then the order is:
 
            Fx12|Fx34|Fy14|Fy23|Fz1|Fz2|Fz3|Fz4
 
Additional plates directly follow with the same assumed channel order. There can be only 1 type of plate 6 or 8 channel at any one time.
 
2) at WORD offset=283 Plate dimension units

 

   at WORD offset=296 Plate Type 0=Kistler 1=AMTI 2=Bertec

 

  at WORD offset=310 #Plates on system

 

   at WORD offset=311 for 2 plates 6 element dimension description

 

         1=”X” Distance centerline to transducers

 

         2=”Y” Distance centerline to transducers

 

         3=Depth beneath plate surface for the transducers [always positive]

 

         4=”X” length

 

         5=”Y” length

 

   at WORD offset=335 orientation of 2nd plate relative to 1st.

 

The only item of interest in the EXTENVREC is

 

   at WORD offset=103 Force units for the plate. 1=Nt 2=Kg 3=Lb

 

Here is code for calculating Fxyz, Mxyz for a Kistler plate. GetVal(channel, sample#) returns the channel value for specified sample# in user units.

 

}
  – m_sc.GetVal(iChan1st+3,lIndx)));
   (m_sc.GetVal(iChan1st+2,lIndx)
  + m_sc.GetVal(iChan1st+1,lIndx)) + plateDims.fA*
  (-m_sc.GetVal(iChan1st,lIndx)
 return(plateDims.fB*
{
//  Override Base class member
float KISTLER::RtnMz(LONG lIndx)
/***************************************************************/
}
  – m_sc.GetVal(iChan1st+7,lIndx)));
  + m_sc.GetVal(iChan1st+6,lIndx)
  + m_sc.GetVal(iChan1st+5,lIndx)
  (-m_sc.GetVal(iChan1st+4,lIndx)
 return(plateDims.fA*
{
//  Override Base class member
float KISTLER::RtnMy(LONG lIndx)
/***************************************************************/
}
  – m_sc.GetVal(iChan1st+7,lIndx)));
  – m_sc.GetVal(iChan1st+6,lIndx)
  + m_sc.GetVal(iChan1st+5,lIndx)
   (m_sc.GetVal(iChan1st+4,lIndx)
 return(plateDims.fB*
{
//  Override Base class member
float KISTLER::RtnMx(LONG lIndx)
/***************************************************************/
}
 return(xRet);
  xRet+=m_sc.GetVal(iChan1st+i+4,lIndx);
 for (int i=0;i<4;i++)
 float xRet=0.;
{
//  Override Base class member
float KISTLER::RtnFz(LONG lIndx)
/***************************************************************/
}
 return(xRet);
  xRet+=m_sc.GetVal(iChan1st+i+2,lIndx);
 for (int i=0;i<2;i++)
 float xRet=0.;
{
//  Override Base class member
float KISTLER::RtnFy(LONG lIndx)
/***************************************************************/
}
 return(xRet);
  xRet+=m_sc.GetVal(iChan1st+i,lIndx);
 for (int i=0;i<2;i++)
 float xRet=0.;
{
//  Override Base class member
float KISTLER::RtnFx(LONG lIndx)
/***************************************************************/

 

From Fxyz & Mxyz the center of pressure and the free moment can be calculated as follows:

 

}
 return(xRet);
  xRet=0.;
 else
   + RtnFx(lIndx)*RtnAy(lIndx);
  xRet=RtnMz(lIndx) – RtnFy(lIndx)*RtnAx(lIndx)
 if (fz>fThresh)
 float xRet,fz=RtnFz(lIndx);
{
// lIndx- sample frame [offset one]
//  Returns Moment-Zfree value for plate
float FORCE_PLATE::RtnMzfree(LONG lIndx)
/***************************************************************/
}
 return(xRet);
 }
   xRet=0.;
  if (xRet<(-plateDims.fLy/2.) || xRet>plateDims.fLy/2.) // Off Plate?
  xRet=(RtnFy(lIndx)*plateDims.fAz+RtnMx(lIndx))/fz;
 {
 if (fz>fThresh)
 float xRet=0.,fz=RtnFz(lIndx);
{
// lIndx- sample frame [offset one]
//  Returns COP-Y value for plate
float FORCE_PLATE::RtnAy(LONG lIndx)
/***************************************************************/
}
 return(xRet);
  xRet=0.;
 else
 }
   xRet=0.;
Plate?file://Off   if (xRet<(-plateDims.fLx/2.) || xRet>plateDims.fLx/2.) 
  xRet=(RtnFx(lIndx)*plateDims.fAz-RtnMy(lIndx))/fz;
 {
 if (fz>fThresh)
 float xRet,fz=RtnFz(lIndx);
{
// lIndx- sample frame [offset one]
//  Returns COP-X value for plate
float FORCE_PLATE::RtnAx(LONG lIndx)
/***************************************************************/

 

I hope this helps. I am leaving Fri 2/18 for a week so fire away before I leave with more questions.

 

Best, Jeremy
 
I am attempting to write an ANA-file loader for the APAS Gait, but this is not trivial. I already ironed out some problems with the basic types (int, short, float) due to Intel’s non-standard byte-ordering.I would like to verify what I need from the ANA-files for reading force and torque data from either 1 or 2 force platforms.

 

My only sources of information are some poorly documented Matlab files (attached) and the documentation from the web. From this I understood there may be multiple trials in one file. I figured out how to get to the trial names, and get data from a user-selected trial.

My question is:

Is the method in the MatLab-files for calculating forces and torques from the trial data block correct? For either 1 or 2 platforms? Apparently the total number of samples divided by the number of channels will give the number of datapoints per channel, correct? Then in FORCE.M the final mappings are done to map channel data to actual forces and torques, using 2 conversion factors and an offset from the environment block. Is this calculation correct? Are these channels always in the same order? Or should I assume the same channel names? And are they always present, even with 1 platform?

 

Any hints, tips, advice are most welcome.
 
Thanks so much for your help. Hope to hear from you.
 
– Rudolf