sfcontour is a program for generating contour plots of 2-D data. It shares many of its parameters with other 2-D plotting programs, such as

**sfgrey** and

**sfgraph**. You can access these parameters by running

**sfdoc stdplot**.

Let us discuss some of the parameters specific to

**sfcontour**.

The number of contours, their origin and increment are given by

**nc=**,

**c0=**,

**dc=**. If these parameters are not specified, they are determined from the data values. The contour lines in the following picture from

jsg/agath/radon were created with

**sfcontour c0=10 dc=10 nc=10**
Alternatively, the contours can be specified in a list with

**c=** or in a file with

**cfile=**.

By default, sfcontour plots only contours for the positive values of the input. If you want both positive and negative values to be represented, use

**allpos=n**.

A 3-D version of

**sfcontour** is

sfcontour3.

The contour lines in the following picture from

jsg/flat/comaz were created with

**sfcontour3 cfile=**
sfsmooth, one of the most useful Madagascar programs, implements smoothing by triangle filtering. The idea of triangle filtering is explained in Jon Claerbout's books Processing versus Inversion and Image Estimation by Example. You can find the explan

Weblog:Madagascar development blogTracked:Jan 12, 12:33sfspectra computes spectrum, the absolute value of the 1-D Fourier transform along the fast axis. The following example from rsf/su/rsfkasper shows a seismic shot gather before and after high-pass filtering and the corresponding spectra computed with

Weblog:Madagascar development blogTracked:Mar 18, 17:16sfgrey3 generates "cube" plots from 3-D data. A cube plot displays sections from a 3-D cube as faces of the cube. Some of the options specific to this kind of display are: flat= The flat parameter tells sfgrey3 whether to display the cube as a

Weblog:Madagascar development blogTracked:Apr 09, 12:42sfderiv applies the first derivative filter. The algorithm implemented in this program is described in the paper Pei, S.-C., and P.-H. Wang, 2001, Closed-form design of maximally flat FIR Hilbert transformers, differentiators, and fractional delaye

Weblog:Madagascar development blogTracked:May 06, 08:10sfderiv applies the first derivative filter. The algorithm implemented in this program is described in the paper Pei, S.-C., and P.-H. Wang, 2001, Closed-form design of maximally flat FIR Hilbert transformers, differentiators, and fractional delaye

Weblog:Madagascar development blogTracked:May 06, 08:11sfderiv applies the first derivative filter. The algorithm implemented in this program is described in the paper Pei, S.-C., and P.-H. Wang, 2001, Closed-form design of maximally flat FIR Hilbert transformers, differentiators, and fractional delaye

Weblog:Madagascar development blogTracked:Jun 02, 06:46sfdip estimates a local slope (dip) using the plane-wave destruction algorithm. The dip is measured in time samples. If α is the dip angle, then the output of sfdip corresponds to the dimensionless quantity p=tanα. The following example

Weblog:Madagascar development blogTracked:Jun 04, 05:46sffft3 implements a complex-to-complex Fast Fourier Transform (FFT) along an arbitrary axis. The FFT library that Madagascar uses is KISS FFT, created by Mark Borgerding. KISS stands for Keep it simple, Stupid! KISS FFT may not be as fast as FFTW but i

Weblog:Madagascar development blogTracked:Jul 08, 12:34Previous programs of the month:sffft3sfdipsfderivsfgrey3sfspectrasfnoisesfgraphsfclipsfagcsfenvelopesfcontoursfsmooth

Weblog:Madagascar development blogTracked:Sep 03, 14:02sfpick performs automatic picking from semblance-like panels. The underlying algorithm is described in Appendix B of the paper Velocity analysis using AB semblance and is inspired by the method of virtual endoscopy in medical imaging. The following

Weblog:Madagascar development blogTracked:Sep 08, 16:07sfiwarp performs mapping between different coordinates. If you have sampled functions f(x) and y(x), sfiwarp with inv=y (the default) finds sampled f(y). If inv=n, sfiwarp takes f(y) and y(x) and finds f(x). In both cases, the sampled y(x) function is sup

Weblog:Madagascar development blogTracked:Sep 09, 12:52sfpick performs automatic picking from semblance-like panels. The underlying algorithm is described in Appendix B of the paper Velocity analysis using AB semblance and is inspired by the method of virtual endoscopy in medical imaging. The following

Weblog:Madagascar development blogTracked:Sep 09, 12:52