Topic:
Why do my contours appear smoothed when using convergent gridding with faults?

Description:
When gridding a horizon in Basemap+ with convergent gridding and fault
boundaries used for modeling constraints, the contours appear smoothed even
though the smoothing constraint has been set to 0. This does not appear to be
the case when gridding the same horizon without fault boundaries.        

Solution:
In GeoFrame 3.7.x, convergent gridding using fault boundaries as modeling
constraints performs smoothing, even if the smoothing parameter is set to 0.  A
smoothing factor of 5 appears to be applied when using the convergent algorithm
with fault boundaries.  No contour smoothing takes place if fault boundaries are
not used with convergent gridding and the smoothing factor is set to 0.

At the time the convergent gridding algorithm was added to GeoFrame, it was
quite slow.  In order to speed up the gridding operation, a hybrid approach
similar to "Quick Map" (in CPS-3)was designed into the algorithm to make
convergent gridding run as fast as possible in Basemap+.

This approach first uses convergent gridding on the surface without the fault
boundaries because convergent gridding runs much faster in this case.  Then one
or more smoothing passes are applied, but constrained to the data AND the fault
boundaries.  This causes the original unfaulted surface to "warp" so that fault
throw represented in the data is honored.  The resulting algorithm usually
produces reasonable results, and was faster than faulted convergent gridding in
CPS-3.  However, the surface is smoother than one computed entirely unfaulted
with smoothing set to 0.  The two surfaces will look different away from fault
boundaries.

The performance of the faulted convergent gridding algorithm was significantly
improved in CPS-3 in GeoFrame 3.5.  The unfaulted convergent pass is no longer
required.  Similar contour results will be seen away from the fault boundaries
in both the faulted and unfaulted cases.  This algorithm will be available in
Basemap+ in GeoFrame 4.0. 



Last Modified on: 12-AUG-00