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Fold app screenshot.png

Fold* is a fold and trace density app for Android, for use with onshore seismic programs. It was built in Google App Inventor and made available in the Android Market in May 2011.


The app is a straightforward calculator, with corrections for incomplete patch coverage. The application and the equations are based on Norm Cooper's excellent tutorial on designing land 3D seismic surveys[1].


  • Converts between metric and Imperial units
  • Gives qualitative advice about trace density and S/R ratio
  • Email the data to yourself or a colleague
  • Go straight to this web page for help
  • Shake the phone or tap Reset to reset the form (note: some phones are quite sensitive and reset easily)
  • Click on the star for 'about' info


Watch the tutorial on YouTube

The app computes fold F according to the equation

and trace density T using:

using the following parameters:

Maximum offset Xmax
the maximum offset recorded in the patch. If this is not known, and you are more interested in the fold at a given depth, then use the target depth instead.
Source line spacing, S
the distance between source lines.
Source interval, s
the distance between the source points along the source lines.
Receiver line spacing, R
the distance between receiver lines.
Receiver interval, r
the distance between the receiver points (sometimes called 'stations') along the receiver lines.

Incomplete patch

Full, narrow and small patches in Fold*

The normal (full patch) situation is that the maximum useful offset is smaller than the patch. If the patch is smaller than the maximum offset in one of its dimensions, then this is a special case. Tap the Partial patch button to choose one of two scenarios:

  1. The patch is long and thin: Narrow patch, in which case you provide the width of the patch
  2. The patch is smaller than the useful offset: Small patch, in which case you provide the length and width of the patch

These are illustrated by the small figures (right).

If you enter numbers larger than the maximum offset, then they are ignored. Alternatively, just click Revert to full to discard these values.

What's new

New in version 0.5

  • Released 1 July 2011
  • Added database to save designs to the phone's memory; these will persist from one session to the next
  • You can clear everything from the database
  • To accommodate this, we added some hidden buttons; access via More... button
  • Fixed a bug (or at least an ambiguity): patch length L and width W were really the half-length and half-width; now you enter the full length and width
  • Added a small drawing to try to make this clear

New in version 0.4

Scan the code to visit the Market
  • First public version
  • Imperial unit conversion, on the fly (tap any time)
  • Emailable form
  • Tap help to visit wiki page
  • Only requires patch length if Small patch is selected, not used for Narrow patch
  • Offset overrides patch: the app checks to see if patch dimensions are bigger than the given offset and ignores them if they are; previously you could set the patch to be larger than offset and the fold and trace density would go up above what you had started with
  • Gives a small warning if S/R is outside Cooper's recommended range
  • Improved layout with gaps after text boxes
  • Moved Reset button so it's harder to hit by accident

Bugs and deficiencies

  • When partial patches are not selected, the cursor gets stuck in the inactive text field (when using the Next button in the keypad); I have reported this to Google

For future release

  • Marine 3D geometries
  • Non-orthogonal geometries (eg Megabin)
  • A graphical display charting trace density with offset
  • A graphical display showing the geometry
  • Persistence in a database
  • A way to compare different designs
  • Ability to roughly cost a program out

See also

External links


  1. Cooper, N (2004), A world of reality: Designing land 3D programs for signal, noise, and prestack migration (Tutorial), The Leading Edge, October and December 2004.