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c3dexport.m and filtering

Posted: Tue Aug 15, 2023 9:34 am
by rosshm
Hi all,

I've been using the Matlab script "c3dexport.m" to convert C3D files into TRC and MOT files for AddBiomechanics.

Is there a way to replace the data in the osimC3D variable (it's named "c3d" in the code below) with modified data, before writing the data to the TRC and MOT files? Filtering/smoothing is specifically what I'll be doing. I can alter the data in the "markerStruct" and "forceStruct" Matlab structures but it's not clear to me how I stuff those back into the c3d variable.

Thanks,
Ross

Code: Select all

% ----------------------------------------------------------------------- %
% The OpenSim API is a toolkit for musculoskeletal modeling and           %
% simulation. See http://opensim.stanford.edu and the NOTICE file         %
% for more information. OpenSim is developed at Stanford University       %
% and supported by the US National Institutes of Health (U54 GM072970,    %
% R24 HD065690) and by DARPA through the Warrior Web program.             %
%                                                                         %
% Copyright (c) 2005-2018 Stanford University and the Authors             %
% Author(s): James Dunne                                                  %
%                                                                         %
% Licensed under the Apache License, Version 2.0 (the "License");         %
% you may not use this file except in compliance with the License.        %
% You may obtain a copy of the License at                                 %
% http://www.apache.org/licenses/LICENSE-2.0.                             %
%                                                                         %
% Unless required by applicable law or agreed to in writing, software     %
% distributed under the License is distributed on an "AS IS" BASIS,       %
% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or         %
% implied. See the License for the specific language governing            %
% permissions and limitations under the License.                          %
% ----------------------------------------------------------------------- %

%% Example of using the Matlab-OpenSim class 

%% Load OpenSim libs
import org.opensim.modeling.*

%% Get the path to a C3D file
[filename, path] = uigetfile('*.c3d');
c3dpath = fullfile(path,filename);

%% Construct an opensimC3D object with input c3d path
% Constructor takes full path to c3d file and an integer for forceplate
% representation (1 = COP). 
c3d = osimC3D(c3dpath,0);

%% Get some stats...
% Get the number of marker trajectories
nTrajectories = c3d.getNumTrajectories();
% Get the marker data rate
rMakers = c3d.getRate_marker();
% Get the number of forces 
nForces = c3d.getNumForces();
% Get the force data rate
rForces = c3d.getRate_force();

% Get Start and end time
t0 = c3d.getStartTime();
tn = c3d.getEndTime();

%% Rotate the data 
c3d.rotateData('x',-90)

%% Get the c3d in different forms
% Get OpenSim tables
markerTable = c3d.getTable_markers();
forceTable = c3d.getTable_forces();
% Get as Matlab Structures
[markerStruct forceStruct] = c3d.getAsStructs();

%% Convert COP (mm to m) and Moments (Nmm to Nm)
c3d.convertMillimeters2Meters();

%% Write the marker and force data to file

% Write marker data to trc file.
% c3d.writeTRC()                       Write to dir of input c3d.
% c3d.writeTRC('Walking.trc')          Write to dir of input c3d with defined file name.
% c3d.writeTRC('C:/data/Walking.trc')  Write to defined path input path.
c3d.writeTRC('walk1_markers.trc');

% Write force data to mot file.
% c3d.writeMOT()                       Write to dir of input c3d.
% c3d.writeMOT('Walking.mot')          Write to dir of input c3d with defined file name.
% c3d.writeMOT('C:/data/Walking.mot')  Write to defined path input path.
% 
% This function assumes point and torque data are in mm and Nmm and
% converts them to m and Nm. If your C3D is already in M and Nm,
% comment out the internal function convertMillimeters2Meters()
c3d.writeMOT('walk1_forces.mot');

Re: c3dexport.m and filtering

Posted: Thu Aug 17, 2023 9:17 am
by kernalnet
Hi, if I understand correctly, you are trying to write your processed markers and GRF data to TRC and MOT files. I'm not sure if it's possible to convert your data back to a C3DFileAdapter object (developers can confirm). But according to osimC3D.m file, you can convert your markerStruct and forceStruct to TRC and MOT files, respectively.

markerStruct to TRC:

Code: Select all

markerRate = markerTable.getTableMetaDataAsString('DataRate');
markerUnit = markerTable.getTableMetaDataString('Units');

markerTableProc = osimTableFromStruct(markerStruct);
markerTableProc.addTableMetaDataString('DataRate', markerRate);
markerTableProc.addTableMetaDataString('Units', markerUnit);
TRCFileAdapter.write(markerTableProc, [path, 'markers.trc']);
forceStruct to MOT:

Code: Select all

% construct new labels
label = {'f', 'p', 'm'};
forceLabels = StdVectorString();

for i = 1:nForces
    for j = 1:3
    labelTemp = label{j};
        if labelTemp == 'f'
            forceLabels.add(['ground_force_', num2str(i), '_v']);
        elseif labelTemp == 'p'
            forceLabels.add(['ground_force_', num2str(i), '_p']);
        elseif labelTemp == 'm'
            forceLabels.add(['ground_moment_', num2str(i), '_m']);
        end
    end
end

forceTableProc = osimTableFromStruct(forceStruct);
forceTableProc.setColumnLabels(forceLabels);
postfix = StdVectorString(); postfix.add('x'); postfix.add('y'); postfix.add('z');
forceFlat = forceTableProc.flatten(postfix);
forceFlat.addTableMetaDataString('nColumns', num2str(forceFlat.getNumColumns()+1));
forceFlat.addTableMetaDataString('nRows', num2str(forceFlat.getNumRows()));
STOFileAdapter.write(forceFlat, [path, 'forces.mot']);
This may require some adjustments (I don't have MATLAB and hence, can't test it; sorry).

Hope this helps.
Mohammadreza