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--- visual3d:documentation:pipeline:metric_commands:metric_compute_dft_coefficients [2024/07/12 13:30] – removed sgranger
+++ visual3d:documentation:pipeline:metric_commands:metric_compute_dft_coefficients [2025/09/23 15:08] (current) – [Examples] wikisysop
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+=====Metric Compute DFT Coefficients=====
+====Overview====
+Metric Compute DFT Coefficients is used to compute a metric signal containing the DFT coefficients and the Base Frequency. It can be found in the **Pipeline Workshop** within the **Metric** folder. This command can be used when it is necessary to perform processing and filtering on a signal to identify the frequency spectrum and/or response.
+The form of the DFT is as follows:
+p(t)= p0 + p1 sin(**w** t) + p2 cos(**w** t) + p3 sin(2**w** t) + p4 cos(2 **w** t) + ....
+where **w** = 2 * PI * Base_Frequency
+The distinct difference between a DFT and an FFT is that the DFT allows the user the option to specify the base frequency.
+This is useful if you want to compare the coefficients across trials and/or across subjects. It also means that the base frequency has physical meaning, such as stride frequency.
+See also [[Visual3D:Documentation:Pipeline:Metric_Commands:Metric_Compute_Power_From_DFT_Coefficients|Compute Power from DFT coefficients]]
+====Pipeline Command====
+The command, as seen in the pipeline workshop, is below.
+<code>
+Metric_Compute_DFT_Coefficients
+/SIGNAL_TYPES=
+! /SIGNAL_FOLDER=ORIGINAL
+! /SIGNAL_NAMES=
+! /SIGNAL_COMPONENTS=ALL_COMPONENTS
+! /RESULT_FOLDER=DFT
+! /RESULT_SUFFIX=_DFT
+! /EVENT_SEQUENCE=
+! /EXCLUDE_EVENTS=
+! /START_FRAME=
+! /END_FRAME=
+! /BASE_FREQUENCY=
+! /NUM_FREQUENCIES=4
+</code>
+====Command Parameters====
+The following table shows the command parameters and descriptions:
+|**SIGNAL_TYPES** |**Specify signal types**|
+|**SIGNAL_FOLDER**|**Specify signal folder**|
+|**SIGNAL_NAMES**|**Specify signal names**|
+|**SIGNAL_COMPONENTS**|**Each component of the signal will generate a metric signal containing the coefficients for that component of the signal.**|
+|**RESULT_FOLDER**|**Specify folder containing results**|
+|**RESULT_SUFFIX**|**Specify suffix applied to results**|
+|**EVENT_SEQUENCE**|**The [[Visual3D:Documentation:C3D_Signal_Types:EVENT_LABEL_Data_Type#Event_Sequence|Event Sequence and Exclude_Sequence]] define the range of frames used to compute the DFT coefficients.**|
+|**EXCLUDE_EVENTS**|**If this event occurs before the first and last event, do not compute a metric**|
+|**START_FRAME**|**Specify the starting frame of the sequence**|
+|**END_FRAME**|**Specify the ending frame of the sequence**|
+|**BASE_FREQUENCY**|**The base frequency is the fundamental frequency of the signal**|
+|**NUM_FREQUENCIES**|**Determines the number of coefficients that will be stored in the resulting metric signal.**|
+====Dialog====
+The command can be edited in a text editor or in a dialog form. To edit in the dialog pop up form either click on the **Edit** button in the pipeline workshop or double-click on the pipeline command. The dialog is shown below.
+{{:ComputeDFTdialog.jpg}}
+The dialog box allows you to assign values to the command parameters outlined above.
+====Examples====
+===Simple example: Compute DFT coefficients for Analog signals===
+One of the primary applications of the **Compute DFT Coefficients** command is to perform analysis of analog signals like force readings and EMGs. Here we compute the DFT coefficients for a folder containing EMG and force plate data.
+Start by identifying the name and location of the intended folder, this can be done in the **Signals and Events** tab.
+{{:visual3d:documentation:pipeline:metric_commands:dft_tutorial_folder.png?250|}}
+Now, add the **Compute DFT Coefficients** command to your pipeline and modify it to include the intended folder, with the event sequence defined for the right stance phase. It should look something like this:
+<code>
+Metric_Compute_DFT_Coefficients
+/SIGNAL_TYPES=ANALOG
+/SIGNAL_FOLDER=ORIGINAL
+/SIGNAL_NAMES=EMG*
+! /SIGNAL_COMPONENTS=ALL_COMPONENTS
+/RESULT_FOLDER=DFT
+! /RESULT_SUFFIX=_DFT
+/EVENT_SEQUENCE=RON+ROFF
+! /EXCLUDE_EVENTS=
+! /START_FRAME=
+! /END_FRAME=
+! /BASE_FREQUENCY=
+! /NUM_FREQUENCIES=4
+;
+</code>
+Click **Execute Pipeline** and navigate back to the **Signals and Events** tab. You should now see a **DFT** folder within the **Metric** folder containing the coefficients for each processed signal.
+===Complex example===
+To see how this command can be used to compute EMG power data please go to [[Visual3D:Documentation:Pipeline:Metric_Commands:Metric_Compute_Power_From_DFT_Coefficients|Compute Power from DFT coefficients]].