Read conversion rule from a mdfObj

My Matlab script reads mf4 files from a large measurement campaign. Each signal has a coversion rule (as explained here: Conversion rules) and in addition numerical quantities can be replaced by textual descriptions.

With the setting Conversion="all" you also get this textual description, but I need this description separately to be able to overwrite the numerical y-value with the respective textual description.

My workaround is to load the data with the option Conversion="all" and without this option. Then I can derive the mapping myself.

Is there a better way to do this?

My hope was that this parameter (text description) can be found in one of the properties, e.g. here in signal.Properties.CustomProperties

Unfortunately, I have not found anything yet. Therefore I am grateful for any hints.

mdfObj = mdf(filename);
Data = read(mdfObj, GroupNo, Channel, IncludeMetadata=true);
Data_all = read(mdfObj, GroupNo, Channel, IncludeMetadata=true, Conversion="all");

Answer 1

[Harsha Vardhan]

Hi,

I understand that you are trying to read both the raw data as well as the converted data (called as physical data) using a single read of the file. And then you want to map the corresponding raw and physical data of a signal.

Either Properties or Properties.CustomProperties does not have the conversions stored

I tried the following approach to check if such converted data is available in the Properties or Properties.CustomProperties of the returned table.

openExample('vnt/ReadingDataWithConversionFromAnMDFFileExample')
mdfObj = mdf("MDF_Conversion_Example.mf4");
data = read(mdfObj,1,"Gear position",IncludeMetadata=true) %Reading "Gear Position" channel data without conversion
   

Output of the table

data =

5×1 timetable

Time      GearPosition
________    ____________

0 sec            2      
0.25 sec         3      
0.5 sec          0      
0.75 sec         2      
1 sec            1   

Now, reading with conversion enabled as seen below

data_all  = read(mdfObj, 1, "Gear position", IncludeMetadata=true, Conversion="All") %Reading with Conversion enabled
data_all =
5×1 timetable

       Time         GearPosition    
     ________    ___________________
  
     0 sec       {'Gear position 2'}
     0.25 sec    {'Gear position 3'}
     0.5 sec     {'Invalid'        }
     0.75 sec    {'Gear position 2'}
     1 sec       {'Gear position 1'}

Next, the I anlayzed the Properties and Properties.CustomProperties of the table.

     data_all.Properties.CustomProperties
      ans = 
       
      CustomProperties with properties:
       
          ChannelGroupAcquisitionName: "Signal with conversions"
                  ChannelGroupComment: ""
     
               ChannelGroupSourceInfo: [1×1 struct]
                   ChannelDisplayName: ""
                       ChannelComment: ""
                          ChannelUnit: ""
                          ChannelType: FixedLength
                      ChannelDataType: IntegerUnsignedLittleEndian
                       ChannelNumBits: 8
                 ChannelComponentType: None
               ChannelCompositionType: None
                    ChannelSourceInfo: [1×1 struct]
                    ChannelReadOption: All
      data_all.Properties
      ans = 
       
        TimetableProperties with properties:
       
                          Description: 'Signal with conversions'
                             UserData: []
                       DimensionNames: {'Time'  'Variables'}
                        VariableNames: {'GearPosition'}
                 VariableDescriptions: {'Gear position'}
                        VariableUnits: {''}
                   VariableContinuity: []
                             RowTimes: [5×1 duration]
                            StartTime: 0 sec
                           SampleRate: 4
                             TimeStep: 0.25 sec
                               Events: []
       
         Custom Properties (access using t.Properties.CustomProperties.<name>):
          ChannelGroupAcquisitionName: "Signal with conversions"
                  ChannelGroupComment: ""
               ChannelGroupSourceInfo: [1×1 struct]
                   ChannelDisplayName: ""
                       ChannelComment: ""
                          ChannelUnit: ""
                          ChannelType: FixedLength
                      ChannelDataType: IntegerUnsignedLittleEndian
                       ChannelNumBits: 8
                 ChannelComponentType: None
               ChannelCompositionType: None
                    ChannelSourceInfo: [1×1 struct]
                    ChannelReadOption: All

For more information about different ways of reading MDF files, please refer to the MDF file documentation - https://www.mathworks.com/help/vnt/referencelist.html?type=function&category=mdf-files

[Michael Muerken]

You are absolutely right.

I have built a small workaround and load once the raw data and once the physical data (e.g. instead of a 0 is now in the data 'Gear Neutral'). Then I use the unique to find the positions in the physical vector. The disadvantage is that only the occurring physical quantities are captured and not all.