FTGramImage: Display Fourier spectrogram

In hht: The Hilbert-Huang Transform: Tools and Methods

Description

This function displays a Fourier spectrogram using the same plot structure and options as HHGramImage. It uses the function EvolutiveFFT to generate a spectrogram, then wraps it in the same plotting format as HHGramImage.

Usage

FTGramImage(sig, dt, ft, time.span = NULL, freq.span = NULL, 
     amp.span = NULL, blur = NULL, taper=0.05, scaling = "none", grid=TRUE, 
    colorbar=TRUE, backcol=c(0, 0, 0), colormap=NULL, pretty=FALSE, ...)

Arguments

sig	The signal to process
dt	sample rate
ft	Fourier spectrogram options

• ft$nfft is the fft length

• ft$ns is the number of samples in a window

• ft$nov is the number of samples to overlap

time.span	Time span to render spectrogram over. NULL will draw the spectrogram over the entire signal.
freq.span	Frequency span to render spectrogram over. NULL plots everything up to the Nyquist frequency.
amp.span	Amplitude range to plot. NULL plots everything.
blur	Apply a Gaussian smoother. Default NULL - no smoothing

.

• blur$sigma is a scalar or two-element vector giving the standard deviation of the Gaussian kernel.

• blur$bleed determines whether to allow values to bleed out of the domain of the image. Default TRUE

taper	Taper value to use for spectrogram (default is 0.05), see spec.taper in the base package.
scaling	determines whether to apply logarithmic (log), or square root (sqrt) scaling to the amplitude data
grid	Boolean - whether to display grid lines or not
colorbar	Boolean - whether to display amplitude colorbar or not
backcol	What background color to use behind the spectrogram, in a 3 element vector: c(red, green, blue)
colormap	What palette object to use for the spectrogram, defaults to rainbow
pretty	Boolean - choose nice axes values, some adjustment may result
...	This function supports some optional parameters as well: trace.format - the format of the trace minima and maxima in sprintf format img.x.format - the format of the X axis labels of the image in sprintf format img.y.format - the format of the Y axis labels of the image in sprintf format colorbar.format - the format of the colorbar labels in sprintf format cex.lab - the font size of the image axis labels cex.colorbar - the font size of the colorbar cex.trace - the font size of the trace axis labels img.x.lab - the X - axis label of the image, it defaults to "time" img.y.lab- the Y - axis label of the image, it defaults to "frequency" main - figure title

Details

This function is a simple Fourier spectrogram plotter. It's useful to compare this image with images generated by HHGramImage to see how the Fourier and Hilbert spectrograms differ.

Value

img	The spectrogram image, suitable for plotting with the generic image function

Author(s)

Daniel Bowman [e-mail]

References

Jonathan M. Lees (2012). RSEIS: Seismic Time Series Analysis Tools. R package version 3.0-6. http://CRAN.R-project.org/package=RSEIS

See Also

HHGramImage, EvolutiveFFT

Examples

data(PortFosterEvent)

dt <- mean(diff(tt))

ft <- list()
ft$nfft <- 4096
ft$ns <- 30
ft$nov <- 29

time.span <- c(5, 10)
freq.span <- c(0, 25)
amp.span <- c(1e-5, 0.0003)
FTGramImage(sig, dt, ft, time.span = time.span, freq.span = freq.span, 
    amp.span = amp.span, pretty = TRUE, img.x.format = "%.1f",
    img.y.format = "%.0f",
    main = "Port Foster Event - Fourier Spectrogram")

Example output

Adjusting Time and Frequency limits to nice looking numbers (the "pretty" option is currently set to TRUE)

hht documentation built on March 28, 2021, 9:11 a.m.