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SEP3D Review

SEP3D is a powerful extension to the original SEPlib hypercube format. SEP3D attempts to build as much as possible on top of the original hypercube format. As a result, a SEP3D dataset is to some extent an amalgamation of two or three SEPlib datasets. Traditionally SEPlib files are composed of two parts, an ASCII description file and a binary data file. The ASCII file provides a description and a pointer to the binary file (by default ending in @). Below is a summary of the three ASCII/binary pairs.
History/Data
This is exactly the same as the original SEP hypercube with the limitation that the hypercube is 2-D, simply a collection of 1-D vectors (e.g. seismic traces). The history file contains pointers to the other potential file pairs: header format file (HFF, ending in H@@) and headers (ending in H@@@), and grid format file (GFF, ending ing H@@@@) and the grid (ending ing H@@@@@@).
HFF/Headers
This pair contains information about the 1-D vectors in the data file. It is at least a 2-D, and possibly higher dimension, hyper-cube. The first dimension is the number of headers associated with the vectors. Each header is described in the HFF by name, type, and format. In addition the headers can contain a special key, the data_record_number, which provides a pointer into the data file. For example, a header with a data_record_number of 5 would indicate it is associated with the fifth header in the data file.
GFF/Grid
The grid and the GFF are optional portions of a SEP3D dataset. The grid attaches the axes of a hypercube onto a fundamentally irregular dataset. For example, imagine you have an irregular dataset that is a function of the coordinate x and y. You could impose a 2-D grid on the data described by its origin (ox and dx), sampling (dx and dy), and length (nx and ny). At each grid cell you will then have a range of possible x and y locations (ox+dx*ix:ox+dx*(ix+1), oy+dy*iy:oy+dy*(iy+1)). The grid will contain a list of the headers that fall within these grid limits.
SEP3D allows a significant amount of flexibility. Any dataset can have from 1-3 of these files. There is no set standard of key names or key types. The grid can be constructed in any manner. Operations can be performed on the headers and grid without accessing the data. The coding overhead to allow this flexibility is significant.
next up previous print clean
Next: DESIGN Up: R. Clapp: SEPlib programming Previous: R. Clapp: SEPlib programming
Stanford Exploration Project
7/8/2003