- makes a compressed copy of a pyramid structure
cxPyramid *cxPyrCompress(cxPyramid *src, cxPyramidDictionary *dict, long layer)
integer function cxPyrCompress(src, dict, layer)
Input pyramid data structure.
Input pyramid dictionary data structure.
Input layer from which to compress.
FUNCTION RETURN VALUE
The returned value for this function is a pointer to the newly compressed
cxPyrCompress makes a compressed copy of its input pyramid,
replacing all cxConnection structures of the input pyramid from layer
layer to the base with a single cxConnection.
cxPyrCompress thus makes a new pyramid in which the elements of
src at layer are no longer created as hierarchical
elements, but rather by reference to a dictionary of canonical
elements. Each compressed element lists its vertices by index into the
base lattice, along with an index of the dictionary element it
If dict is not null, it is used as the starting dictionary; if
it is null the default dictionary for the destination layer is
used. The dictionary of reference elements in the output is created as
a union of the input dict or default dictionary (see
cxPyrDictDefault(3E)) and the other elements found in the
The value of layer may range from one up to the number of layers
in the pyramid. A compression layer of three is normal,
indicating that 3-D elements are to be represented by the canonical
reference elements in the pyramid dictionary. Compression at layer
three suppresses representation of the internal faces and edges in a
pyramid; in a large mesh of a given element type, this suppression can
save significant amounts of storage.
A compression layer of two indicates that faces are represented
by the canonical polygons (triangles, quadrilaterals, and other
polygons found in src). While a compression layer of one
indicates that lines will be compressed, there is no savings of
storage in this case.
The storage required to represent a compressed pyramid is often
much less than that of the equivalent expanded pyramid, depending on
the layer of compression. However, a compression layer other than three
or two may actually increase storage requirements.
cxPyrCompress can be used to recompress compressed pyramids
at a different layer. Recompressing at a higher level may take a long
time and is not advised.
cxPyrCompress returns a NULL if its input is malformed or if an
allocation error occurs. The returned pyramid is a reference counted
structure owned by the caller.
Last modified: Mon Nov 6 16:33:43 GMT 2000
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© The Numerical Algorithms Group Ltd, Oxford UK. 1996