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Commit 43ecb5b8 authored by Christophe Geuzaine's avatar Christophe Geuzaine
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clarify orientation change with negative physical numbers (cf. #333)

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...@@ -1796,15 +1796,15 @@ ways, for example using the @code{Translate}, @code{Rotate}, ...@@ -1796,15 +1796,15 @@ ways, for example using the @code{Translate}, @code{Rotate},
references them. Zero or negative identification numbers are reserved by references them. Zero or negative identification numbers are reserved by
the system for special uses: do not use them in your scripts. the system for special uses: do not use them in your scripts.
Groups of elementary geometrical entities can also be defined and Groups of elementary geometrical entities can also be defined and are
are called ``physical'' entities. These physical entities cannot be modified called ``physical'' entities. These physical entities cannot be modified
by geometry commands: their only purpose is to assemble elementary entities by geometry commands: their only purpose is to assemble elementary
into larger groups, possibly modifying their orientation, so that they can entities into larger groups so that they can be referred to by the mesh
be referred to by the mesh module as single entities. As is the case with module as single entities. As is the case with elementary entities, each
elementary entities, each physical point, physical line, physical surface or physical point, physical line, physical surface or physical volume must
physical volume must be assigned a unique identification number. See be assigned a unique identification number. See @ref{Mesh module}, for
@ref{Mesh module}, for more information about how physical entities affect more information about how physical entities affect the way meshes are
the way meshes are saved. saved.
@menu @menu
* Geometry commands:: * Geometry commands::
...@@ -1968,7 +1968,7 @@ the comma) or not (in which case a unique identification number is ...@@ -1968,7 +1968,7 @@ the comma) or not (in which case a unique identification number is
automatically created). Specifying negative identification numbers in automatically created). Specifying negative identification numbers in
the @var{expression-list} will reverse the orientation of the mesh the @var{expression-list} will reverse the orientation of the mesh
elements belonging to the corresponding elementary lines in the saved elements belonging to the corresponding elementary lines in the saved
mesh. mesh file.
@end ftable @end ftable
...@@ -2051,7 +2051,7 @@ which can be either provided explicitly (after the comma) or not (in ...@@ -2051,7 +2051,7 @@ which can be either provided explicitly (after the comma) or not (in
which case a unique identification number is automatically created). which case a unique identification number is automatically created).
Specifying negative identification numbers in the @var{expression-list} Specifying negative identification numbers in the @var{expression-list}
will reverse the orientation of the mesh elements belonging to the will reverse the orientation of the mesh elements belonging to the
corresponding elementary surfaces in the saved mesh. corresponding elementary surfaces in the saved mesh file.
@end ftable @end ftable
...@@ -2617,8 +2617,8 @@ inconvenient: ...@@ -2617,8 +2617,8 @@ inconvenient:
mesh elements cannot be duplicated; mesh elements cannot be duplicated;
@item @item
the orientation of the mesh elements (the ordering of their nodes) is the orientation of the mesh elements (the ordering of their nodes) is
determined entirely by the orientation of their ``parent'' elementary determined by the orientation of their ``parent'' elementary
entities, and cannot be modified; entities;
@item @item
elements belonging to different elementary entities cannot be linked as elements belonging to different elementary entities cannot be linked as
being part of a larger group having a physical or mathematical meaning (like being part of a larger group having a physical or mathematical meaning (like
...@@ -2629,21 +2629,23 @@ To remedy these problems, the geometry module (@pxref{Geometry module}) ...@@ -2629,21 +2629,23 @@ To remedy these problems, the geometry module (@pxref{Geometry module})
introduces the notion of ``physical'' entities (also called ``physical introduces the notion of ``physical'' entities (also called ``physical
groups''). The purpose of physical entities is to assemble elementary groups''). The purpose of physical entities is to assemble elementary
entities into larger, possibly overlapping groups, and to control the entities into larger, possibly overlapping groups, and to control the
orientation of the elements in these groups. The introduction of orientation of the elements in these groups when they are save into a
physical entities in large models usually greatly facilitates the mesh file. The introduction of physical entities in large models usually
manipulation of the model (e.g., using `Tools->Visibility' in the GUI) greatly facilitates the manipulation of the model (e.g., using
and the interfacing with external solvers. `Tools->Visibility' in the GUI) and the interfacing with external
solvers.
In the MSH file format (@pxref{File formats}), if physical entities are In the MSH file format (@pxref{File formats}), if physical entities are
defined, the output mesh only contains those elements that belong to defined, the output mesh only contains those elements that belong to
physical entities. Other file formats each treat physical entities in physical entities. Other file formats each treat physical entities in
slightly different ways, depending on their capability to define groups. slightly different ways, depending on their capability to define groups.
In all cases, Gmsh reindexes the mesh vertices and elements so that they Note that in some mesh file formats Gmsh reindexes the mesh vertices and
are numbered in a continuous sequence in the output files. Note that the elements so that they are numbered in a continuous sequence in the
numbers displayed on screen after mesh generation thus usually differ output files. Note that the numbers displayed on screen after mesh
from the ones saved in the mesh files. To check the actual numbers saved generation can thus differ from the ones saved in the mesh files,
in the output file just load the file back using `File->Open'. depending on the format. To check the actual numbers saved in the output
file just load the file back using `File->Open'.
@c ------------------------------------------------------------------------- @c -------------------------------------------------------------------------
@c Mesh commands @c Mesh commands
......
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