Read Physical and Raw Data from MDF Files

This example shows you how to read channel data from an MDF file as physical values and raw values.

Introduction to ASAM MDF Conversion Rules

According to the ASAM MDF standard, a data value encoded in the MDF channel is denoted as a raw value. It can be converted to a physical value with an engineering unit using a conversion rule. Conversion rules are the methods defined at the channel level to convert raw values to physical values.

ASAM MDF V4.2.0 supports the following conversion rules:

No Conversion

CC_Type 0: Identity (“1:1”) conversion

Value to Value Conversions

CC_Type 1: Linear conversion
CC_Type 2: Rational conversion formula
CC_Type 3: Algebraic conversion
CC_Type 4: Value to value tabular look-up with interpolation
CC_Type 5: Value to value tabular look-up without interpolation
CC_Type 6: Value range to value tabular look-up

Value to Text Conversions

CC_Type 7: Value to text/scale conversion tabular look-up
CC_Type 8: Value range to text/scale conversion tabular look-up

Text to Value Conversions

CC_Type 9: Text to value tabular look-up

Text to Text Conversions

CC_Type 10: Text to text tabular look-up

Other Conversion

CC_Type 11: Bitfield text table

The mdfRead function by default reads physical values from an MDF file, but it also provides the capability to read raw values via the ReadRaw option.

ReadRaw is false (default) — Apply all numeric and text conversions (CC_Type 1-10). All data are read as physical values.
ReadRaw is true — Do not apply any conversion. All data are read as raw values.

Note that if there is an identity conversion (CC_Type 0), or a none conversion (no conversion rule) in the channel, the data are read as raw values regardless of the ReadRaw option specified.

View Channel Details

Use the mdfChannelInfo function to view details about all the channels in MDF_Conversion_Example.mf4. Specify the AdditionalMetadata option as true to include the additional metadata, which contains information about the raw data type in DataType and NumBits, as well as conversion rule in ConversionType.

chanInfo = mdfChannelInfo("MDF_Conversion_Example.mf4", AdditionalMetadata=true)

chanInfo=6×25 table
                 Name                 GroupNumber    GroupNumSamples     GroupAcquisitionName      GroupComment        GroupSourceName            GroupSourcePath        DisplayName       Unit          Comment        ExtendedNamePrefix             SourceName                 SourcePath                Type         SyncType             DataType              NumBits    ComponentType    CompositionType    ConversionType    SourceComment    SourceType     SourceBusType    SourceBusChannelNumber    SourceSimulated
    ______________________________    ___________    _______________    _______________________    ____________    _______________________    _______________________    ___________    ___________    ___________    _______________________    _______________________    _______________________    ______________    ________    ___________________________    _______    _____________    _______________    ______________    _____________    ___________    _____________    ______________________    _______________

    "Ambient temperature"                  1                5           Signal with conversions    <undefined>     Signal with conversions    Signal with conversions        ""         °F             <undefined>    <undefined>                <undefined>                <undefined>                FixedLength         None      RealLittleEndian                 64           None              None           Unspecified           ""          Unspecified     Unspecified               0                    false     
    "Engine temperature"                   1                5           Signal with conversions    <undefined>     Signal with conversions    Signal with conversions        ""         °C             <undefined>    <undefined>                <undefined>                <undefined>                FixedLength         None      IntegerSignedLittleEndian        32           None              None           Linear                ""          Unspecified     Unspecified               0                    false     
    "Fault code"                           1                5           Signal with conversions    <undefined>     Signal with conversions    Signal with conversions        ""         <undefined>    <undefined>    <undefined>                <undefined>                <undefined>                VariableLength      None      StringUTF8                       64           None              None           TextToText            ""          Unspecified     Unspecified               0                    false     
    "Gear position"                        1                5           Signal with conversions    <undefined>     Signal with conversions    Signal with conversions        ""         <undefined>    <undefined>    <undefined>                <undefined>                <undefined>                FixedLength         None      IntegerUnsignedLittleEndian       8           None              None           ValueToText           ""          Unspecified     Unspecified               0                    false     
    "Windshield wiper speed level"         1                5           Signal with conversions    <undefined>     Signal with conversions    Signal with conversions        ""         <undefined>    <undefined>    <undefined>                <undefined>                <undefined>                VariableLength      None      StringUTF8                       64           None              None           TextToValue           ""          Unspecified     Unspecified               0                    false     
    "time"                                 1                5           Signal with conversions    <undefined>     Signal with conversions    Signal with conversions        ""         s              <undefined>    Signal with conversions    Signal with conversions    Signal with conversions    Master              Time      RealLittleEndian                 64           None              None           Unspecified           ""          Tool            None                      0                    false

Display only a few relevant variables in the returned table, including Name, GroupNumber, GroupNumSamples, Unit, DataType, NumBits, and ConversionType.

chanInfo(:, ["Name", "GroupNumber", "GroupNumSamples", "Unit", "DataType", "NumBits", "ConversionType"])

ans=6×7 table
                 Name                 GroupNumber    GroupNumSamples       Unit                 DataType              NumBits    ConversionType
    ______________________________    ___________    _______________    ___________    ___________________________    _______    ______________

    "Ambient temperature"                  1                5           °F             RealLittleEndian                 64        Unspecified  
    "Engine temperature"                   1                5           °C             IntegerSignedLittleEndian        32        Linear       
    "Fault code"                           1                5           <undefined>    StringUTF8                       64        TextToText   
    "Gear position"                        1                5           <undefined>    IntegerUnsignedLittleEndian       8        ValueToText  
    "Windshield wiper speed level"         1                5           <undefined>    StringUTF8                       64        TextToValue  
    "time"                                 1                5           s              RealLittleEndian                 64        Unspecified

Read Data from a Channel with Value to Value Conversion

The channel named "Engine temperature" contains Linear conversion (CC_Type 1).

chanInfo.ConversionType(chanInfo.Name == "Engine temperature")

ans = 
  ChannelConversionType enumeration

    Linear

Read data from "Engine temperature". By default, physical values of data type double are returned.

engTempPhy = mdfRead("MDF_Conversion_Example.mf4", Channel="Engine temperature");
engTempPhy{1}

ans=5×1 timetable
          time      Engine temperature
        ________    __________________

        0 sec                 35      
        0.25 sec          35.556      
        0.5 sec           36.111      
        0.75 sec          36.667      
        1 sec             37.222

class(engTempPhy{1}.("Engine temperature"))

ans = 
'double'

Set option ReadRaw set to true to read data from "Engine temperature" as raw values of data type int32. The raw data type is defined in DataType as IntegerSignedLittleEndian (2) and NumBits as 32.

engTempRaw = mdfRead("MDF_Conversion_Example.mf4", Channel="Engine temperature", ReadRaw=true);
engTempRaw{1}

ans=5×1 timetable
          time      Engine temperature
        ________    __________________

        0 sec               95        
        0.25 sec            96        
        0.5 sec             97        
        0.75 sec            98        
        1 sec               99

class(engTempRaw{1}.("Engine temperature"))

ans = 
'int32'

Read Data from a Channel with Value to Text Conversion

The channel named "Gear position" contains ValueToText conversion (CC_Type 7).

chanInfo.ConversionType(chanInfo.Name == "Gear position")

ans = 
  ChannelConversionType enumeration

    ValueToText

Read data from "Gear position". By default, physical values of data type string are returned.

gearPosPhy = mdfRead("MDF_Conversion_Example.mf4", Channel="Gear position");
gearPosPhy{1}

ans=5×1 timetable
          time        Gear position  
        ________    _________________

        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"

class(gearPosPhy{1}.("Gear position"))

ans = 
'string'

Set option ReadRaw set to true to read data from "Gear position" as raw values of data type uint8. The raw data type is defined in DataType as IntegerUnsignedLittleEndian (0) and NumBits as 8.

gearPosRaw = mdfRead("MDF_Conversion_Example.mf4", Channel="Gear position", ReadRaw=true);
gearPosRaw{1}

ans=5×1 timetable
          time      Gear position
        ________    _____________

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

class(gearPosRaw{1}.("Gear position"))

ans = 
'uint8'

Read Data from a Channel with No Conversion

The channel named "Ambient temperature" contains no conversion.

chanInfo.ConversionType(chanInfo.Name == "Ambient temperature")

ans = 
  ChannelConversionType enumeration

    Unspecified

Read data from "Ambient temperature" both as physical values and raw values. Because the channel has no conversion, the returned physical values are identical to the returned raw values.

Note that the physical values have the same data type, double, as the raw values. The raw data type is defined in DataType as RealLittleEndian (4) and NumBits as 64.

ambTempPhy = mdfRead("MDF_Conversion_Example.mf4", Channel="Ambient temperature");
ambTempPhy{1}

ans=5×1 timetable
          time      Ambient temperature
        ________    ___________________

        0 sec              81.7        
        0.25 sec           81.9        
        0.5 sec              82        
        0.75 sec           81.8        
        1 sec              81.9

class(ambTempPhy{1}.("Ambient temperature"))

ans = 
'double'

ambTempRaw = mdfRead("MDF_Conversion_Example.mf4", Channel="Ambient temperature", ReadRaw=true);
ambTempRaw{1}

ans=5×1 timetable
          time      Ambient temperature
        ________    ___________________

        0 sec              81.7        
        0.25 sec           81.9        
        0.5 sec              82        
        0.75 sec           81.8        
        1 sec              81.9

class(ambTempRaw{1}.("Ambient temperature"))

ans = 
'double'

Other Conversion Examples

Two other channels are present in the MDF file.

The channel named "Windshield wiper speed level" contains TextToValue conversion (CC_Type 9).

chanInfo.ConversionType(chanInfo.Name == "Windshield wiper speed level")

ans = 
  ChannelConversionType enumeration

    TextToValue

The channel named "Fault code" contains TextToText conversion (CC_Type 10).

chanInfo.ConversionType(chanInfo.Name == "Fault code")

ans = 
  ChannelConversionType enumeration

    TextToText

You can try reading data from these channels with different ReadRaw options.