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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 [2024/07/17 15:46] (current) – created sgranger
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+====== Metric Compute DFT Coefficients ======
+The Discrete Fourier Transform of a Signal
+This command computes a metric signal containing the DFT coefficients and the Base Frequency.
+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]]
+{{:ComputeDFTdialog.jpg}}
+=== Pipeline Command ===
+**Metric_Compute_DFT_Coefficients**
+/SIGNAL_TYPES=
+! /SIGNAL_NAMES=
+! /SIGNAL_FOLDER=ORIGINAL
+! /SIGNAL_COMPONENTS=ALL_COMPONENTS
+! /RESULT_SUFFIX=_DFT
+! /RESULT_FOLDER=DFT
+!/[[Visual3D:Documentation:C3D_Signal_Types:EVENT_LABEL_Data_Type#Event_Sequence|EVENT_SEQUENCE]]=
+!/[[Visual3D:Documentation:C3D_Signal_Types:EVENT_LABEL_Data_Type#Exclude_Events|EXCLUDE_EVENTS]]=
+! /START_FRAME=
+! /END_FRAME=
+! /USE_POINT_RATE=TRUE
+! /BASE_FREQUENCY=
+/NUM_FREQUENCIES=4
+**;**
+=== Signal_Components ===
+Each component of the signal will generate a metric signal containing the coefficients for that component of the signal.
+=== Number of Frequencies ===
+The parameter Num_Frequencies determines the number of coefficients that will be stored in the resulting metric signal.
+If Num_Frequencies is empty, the number is determined consistent with a standard DFT or FFT.
+Num_Frequencies = 1 + NumFrames/2
+where the Maximum Number of Frequencies = 0.5*DataRate;
+=== 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
+=== Base_Frequency ===
+If BASE_FREQUENCY is empty,
+Frequency= SamplingRate/NumberOfFrames (average per cycle per file)
+Else
+Frequency= Numerical value or Expression
+=== Resulting Metric Signal ===
+The metric signal is stored as follows (Base_Frequency, p0, p1, p2, p3, p4, ....)
+The Base_Frequency and coefficients are stored as components of the signal.
+If there are multiple ranges of data, there will be a "frame" or "row" for each range.
+see also : [[Visual3D:Documentation:Pipeline:Metric_Commands:Metric_Compute_Power_From_DFT_Coefficients|Metric_Compute_Power_From_DFT_Coefficients]]