About HLR Algorithms
Two HLR algorithms can be used to compute a HLR
scene:
- Exact mode which uses exact geometry
- Polyhedral mode which enables to compute
HLR on non-exact geometry that can be found in
third-party data, in CGR files (when working with
the cache system, for instance) or in specific
Version 4 elements.
The Exact mode is more CPU- and memory-intensive than the Polyhedral
mode but gives a more accurate
result.
Note also that HLR and Dynamic Hidden
Line Removal are not computed the same way because
Dynamic Hidden Line Removal is primarily based on the
graphics card. Therefore, discrepancies might appear
between the two results. |
Restrictions
Exact mode
As this mode is based on exact geometry, the result
is more precise. However as explained above, this mode
is CPU- and memory-intensive and some restrictions might
occur in specific cases.
For instance, you might encounter problems with clashing
bodies because some geometrical elements might not be
generated. To by-pass this limitation, you can manually
resolve the intersection topology using an appropriate
sequence of Boolean operations.
Polyhedral mode
In this mode, the geometry's complexity (in terms of
number of triangles for each face of a surface) is
limited. Attributes applied to edges, such as the
lineytpe or the thickness, are those of the original
edges as far as possible. When it is not possible to use
the original attributes, default attributes are applied
instead.
In Polyhedral mode, the smoothness of edges is not
taken into account and therefore, cannot be switched off
or on. |
Behavior in Specific
Applications
When working with the Activating clipping frame,
Clip View or Sectioning command in
a 2D Layout or DMU Sectioning context, the polyhedral
HLR mode is used. In this case, some specific geometry
elements such as curved pipes or cylinders might not be
affected by clipping views, sections or polygonal traps
during the HLR rendering process. |