ibg2.html

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<TITLE>IBG 2.0 - grid generation algorithm</TITLE>

<H1>grid generation algorithm</H1>

 <P>The points obtained by the octree algorithm are used as input for
the Delaunay algorithm. This results in a Delaunay grid.

 <P>Then we assing region numbers to grid cells. Between cells with
different region numbers, we create boundary face cells.

<H2>Known Problems</H2>

<H3>Bad Region Cells</H3>

<A NAME="bad region cell"><H3>Bad Region Cells</H3></A>
 If the boundary faces in the resulting grid look fine, ignore this warning.
<A NAME="end of bad region cell"><hr></A>

 <P>The Delaunay algorithm uses only the information about the point
position.  The resulting Delaunay grid may contain cells which
intersect the boundary faces.

 <P>The main idea how to avoid this is to avoid such situations in the
initial octree algorithm.  Unfortunately this is hard to achieve, and
this algorithm often fails.

 <P>If this happens, we assign the region number of the barycenter to
the critical cell.  This warning also leads to subsequent warnings
about bad face cells:


<A NAME="bad face cell"><H3>Bad Face Cells</H3></A>
 If the boundary edges in the resulting grid look fine, ignore this warning.
<A NAME="end of bad face cell"><hr></A>

 <P>This happens for the same reason as <A HREF="#bad region cell">bad
region cells</A>.  It happens where different boundary faces are close
to each other, thus, especially near boundary edges.