Editing Guide to madagascar programs (section)

=user/fomels programs=
==sfpick==
{| class="wikitable" align="center" cellspacing="0" border="1"
! colspan="4" style="background:#ffdead;" | Automatic picking  from semblance-like panels. 
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! colspan="4" | sfpick < scn.rsf > pik.rsf vel0=o2 niter=100 an=1. gate=3 smooth=y rect#=(1,1,...) rect1=1 rect2=1 ...
|-
|  colspan="4" | rectN defines the size of the smoothing stencil in N-th dimension.<br><br>Theory in Appendix B of:<br>S. Fomel, 2009, <br>Velocity analysis using AB semblance: Geophysical Prospecting, v. 57, 311-321.<br>Reproducible version in RSFSRC/book/jsg/avo 
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| ''float  '' || '''an=1.''' ||   || 	axes anisotropy
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| ''int    '' || '''gate=3''' ||   || 	picking gate
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| ''int    '' || '''niter=100''' ||   || 	number of iterations
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| ''int    '' || '''rect#=(1,1,...)''' ||   || 	smoothing radius on #-th axis
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| ''bool   '' || '''smooth=y''' ||  [y/n] || 	if apply smoothing
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| ''float  '' || '''vel0=o2''' ||   || 	surface velocity
|}
Short description of the algorithm:
# Start from the top (first time slice), pick an initial (source) point, evaluate all other points with the direct traveltime.
# At each grid point at the next level, find the traveltime to points at the previous level, add the traveltimes from the previous level, and select minimum. The aperture (gate= parameter in sfpick) limits the search radius.
# Repeat step 2 until reaching the bottom.
# Pick the minimum traveltime at the bottom and track the ray back to the source by following the traveltime gradient direction.
# Postprocessing (smooth= parameter in sfpick): smooth the picked ray path using shaping regularization.

Many people have discovered and rediscovered the algorithm. The best reference is probably ''V. Meshbey, E. Ragoza, D. Kosloff, U. Egozi, and D. Wexler, 2002, Three-dimensional Travel-time Calculation Based on Fermat's Principle: Pure and Applied Geophysics, v. 159, 1563-1582.''