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Write docs on IOS geometry processing. See #671.
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Dion Moult
@@ -12,5 +12,5 @@ system, as well as high level analysis and authoring functions.
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ifcopenshell-python/installation
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ifcopenshell-python/hello_world
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ifcopenshell-python/code_examples
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ifcopenshell-python/geometry_iterator
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ifcopenshell-python/geometry_processing
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ifcopenshell-python/developer_guide
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@@ -1,53 +0,0 @@
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Geometry iterator
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=================
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IfcOpenShell provides a geometry iterator function to efficiently process
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geometry in an IFC model. The iterator is always used in IfcConvert, and may
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also be invoked in C++ or in Python.
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The geometry iterator makes it easy to collect possible geometry in a model,
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supports multicore processing, and implements caching and reuse to improve the
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efficiency of geometry processing. It is also possible to process geometry one
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by one using ``create_shape()``, but is significantly less efficient.
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By default, the geometry iterator processes all 3D geometry in a model from all
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elements, and returns a list of X Y Z vertex ordinates in a flattend list, as
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well as a flattend list of triangulated faces denoted by vertex indices.
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There are a variety of configuration settings to get different output. For
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example, you may filter elements from processing, extract 2D data, or return
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non-triangulated OpenCASCADE BReps. For more information on the various
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settings, see :doc:`Geometry Settings<../ifcopenshell/geometry_settings>`.
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Here is a simple example in Python:
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.. code-block:: python
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import multiprocessing
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import ifcopenshell
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import ifcopenshell.geom
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ifc_file = ifcopenshell.open('model.ifc')
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settings = ifcopenshell.geom.settings()
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iterator = ifcopenshell.geom.iterator(settings, ifc_file, multiprocessing.cpu_count())
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if iterator.initialize():
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while True:
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shape = iterator.get()
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# Get the current IFC element we are iterating over
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element = ifc_file.by_guid(shape.guid)
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# Indices of vertices per triangle face e.g. [f1v1, f1v2, f1v3, f2v1, f2v2, f2v3, ...]
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faces = shape.geometry.faces
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# X Y Z of vertices in flattened list e.g. [v1x, v1y, v1z, v2x, v2y, v2z, ...]
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verts = shape.geometry.verts
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# Material names and colour style information that are relevant to this shape
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materials = shape.geometry.materials
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# Indices of material applied per triangle face e.g. [f1m, f2m, ...]
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material_ids = shape.geometry.material_ids
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# Since the lists are flattened, you may prefer to group them per
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# face like so depending on your geometry kernel
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grouped_verts = [[verts[i], verts[i + 1], verts[i + 2]] for i in range(0, len(verts), 3)]
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grouped_faces = [[faces[i], faces[i + 1], faces[i + 2]] for i in range(0, len(faces), 3)]
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if not iterator.next():
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break
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@@ -0,0 +1,202 @@
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Geometry processing
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===================
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Geometry is specified in many ways in IFC. Some geometry is defined explicitly
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with coordinates, vertices, and faces. Some geometry is defined implicitly with
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equations, boolean operations, and parametric shapes.
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Individual processing
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---------------------
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The simplest way to process any geometry in a standardised fashion is to use the
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IfcOpenShell ``create_shape()`` function. This will provide a list of vertices,
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edges, and faces, or alternatively an OpenCASCADE BRep.
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Here is a simple example of processing a single wall into a list of vertices and
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faces. In this example, a ``shape`` variable is returned, which holds geometry
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related information in ``shape.geometry``:
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.. code-block:: python
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import ifcopenshell
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import ifcopenshell.geom
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ifc_file = ifcopenshell.open('model.ifc')
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element = ifc_file.by_type('IfcWall')[0]
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settings = ifcopenshell.geom.settings()
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shape = ifcopenshell.geom.create_shape(settings, element)
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# The GUID of the element we processed
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print(shape.guid)
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# The ID of the element we processed
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print(shape.id)
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# The element we are processing
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print(ifc_file.by_guid(shape.guid))
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# A unique geometry ID, useful to check whether or not two geometries are
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# identical for caching and reuse. The naming scheme is:
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# IfcShapeRepresentation.id{-layerset-LayerSet.id}{-material-Material.id}{-openings-[Opening n.id ...]}{-world-coords}
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print(shape.geometry.id())
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# Indices of vertices per triangle face e.g. [f1v1, f1v2, f1v3, f2v1, f2v2, f2v3, ...]
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faces = shape.geometry.faces
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# X Y Z of vertices in flattened list e.g. [v1x, v1y, v1z, v2x, v2y, v2z, ...]
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verts = shape.geometry.verts
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# Since the lists are flattened, you may prefer to group them per face like so depending on your geometry kernel
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grouped_verts = [[verts[i], verts[i + 1], verts[i + 2]] for i in range(0, len(verts), 3)]
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grouped_faces = [[faces[i], faces[i + 1], faces[i + 2]] for i in range(0, len(faces), 3)]
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# A list of styles that are relevant to this shape
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styles = shape.geometry.materials
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for style in styles:
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# Each style is named after the entity class if a default
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# material is applied. Otherwise, it is named "surface-style-{SurfaceStyle.name}"
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# All non-alphanumeric characters are replaced with a "-".
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print(style.original_name)
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# A more human readable name
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print(style.name)
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# Each style may have diffuse colour RGB codes
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if style.has_diffuse:
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print(style.diffuse)
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# Each style may have transparency data
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if style.has_transparency:
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print(style.transparency)
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# Indices of material applied per triangle face e.g. [f1m, f2m, ...]
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material_ids = shape.geometry.material_ids
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Alternatively, you may choose to retrieve an OpenCASCADE BRep:
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.. code-block:: python
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import ifcopenshell
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import ifcopenshell.geom
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ifc_file = ifcopenshell.open('model.ifc')
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element = ifc_file.by_type('IfcWall')[0]
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settings = ifcopenshell.geom.settings()
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settings.set(settings.USE_PYTHON_OPENCASCADE, True)
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try:
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shape = geom.create_shape(settings, element)
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geometry = shape.geometry # see #1124
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# These are methods of the TopoDS_Shape class from pythonOCC
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shape_gpXYZ = geometry.Location().Transformation().TranslationPart()
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# These are methods of the gpXYZ class from pythonOCC
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print(shape_gpXYZ.X(), shape_gpXYZ.Y(), shape_gpXYZ.Z())
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except:
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print("Shape creation failed")
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When an entire element is passed into ``create_shape()``, the 3D representation
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is processed by default with all openings applied. However, it is also possible
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to only process a single shape representation with no openings, representation
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item, or profile definition.
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In these scenarios, a ``geometry`` is returned directly, equivalent to
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``shape.geometry`` in the example above.
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.. code-block:: python
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ifc_file = ifcopenshell.open('model.ifc')
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element = ifc_file.by_type('IfcWall')[0]
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# Process a shape representation
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body = ifcopenshell.util.representation.get_representation(element, "Model", "Body")
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# Note: geometry is returned directly, equivalent to shape.geometry when passing in an element
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geometry = geom.create_shape(settings, body)
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# Process a representation item
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geometry = geom.create_shape(settings, ifc_file.by_type("IfcExtrudedAreaSolid")[0])
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# Process a profile
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geometry = geom.create_shape(settings, ifc_file.by_type("IfcProfileDef")[0])
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Geometry iterator
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-----------------
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IfcOpenShell provides a geometry iterator function to efficiently process
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geometry in an IFC model. The iterator is always used in IfcConvert, and may
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also be invoked in C++ or in Python. It offers the same features as the
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``create_shape()`` function for `Individual processing`_.
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The geometry iterator makes it easy to collect possible geometry in a model,
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supports multicore processing, and implements caching and reuse to improve the
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efficiency of geometry processing. For any bulk geometry processing, it is
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always recommended to use the iterator.
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By default, the geometry iterator processes all 3D geometry in a model from all
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elements, and returns a list of X Y Z vertex ordinates in a flattened list, as
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well as a flattened list of triangulated faces denoted by vertex indices.
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There are a variety of configuration settings to get different output. For
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example, you may filter elements from processing, extract 2D data, or return
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non-triangulated OpenCASCADE BReps. For more information on the various
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settings, see :doc:`Geometry Settings<../ifcopenshell/geometry_settings>`.
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Here is a simple example in Python:
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.. code-block:: python
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import multiprocessing
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import ifcopenshell
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import ifcopenshell.geom
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ifc_file = ifcopenshell.open('model.ifc')
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settings = ifcopenshell.geom.settings()
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iterator = ifcopenshell.geom.iterator(settings, ifc_file, multiprocessing.cpu_count())
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if iterator.initialize():
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while True:
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shape = iterator.get()
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faces = shape.geometry.faces
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verts = shape.geometry.verts
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materials = shape.geometry.materials
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material_ids = shape.geometry.material_ids
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# ... write code to process geometry here ...
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if not iterator.next():
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break
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.. note::
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The iterator can only be used to process whole elements, not individual
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shape representations, representation items, and profiles.
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Manual parsing
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--------------
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IfcOpenShell lets you traverse any IFC entity graph. This means it is possible
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for you to manually browse through the ``Representation`` attribute of IFC
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elements, and parse the corresponding IFC shape representations yourself instead
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of using generic geometric processing such as `Individual processing`_ and the
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`Geometry iterator`_.
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This approach requires an in-depth understanding of IFC geometry
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representations, as well as its many caveats with units and transformations, but
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can be very simple and extremely fast to extract specific types of geometry. For
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example, if you know you are dealing with IfcCircle geometry, you can
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specifically pinpoint the Radius parameter.
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.. code-block:: python
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unit_scale = ifcopenshell.util.unit.calculate_unit_scale(ifc_file)
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for circle in ifc_file.by_type("IfcCircle"):
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# In project length units
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print(circle.Radius)
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# In SI meters
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print(circle.Radius * unit_scale)
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Given the advanced nature of manual processing, it is generally not recommended
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except in specific tasks.
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@@ -41,8 +41,8 @@ utility:
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Exactly how it is run depends on the recipe. A recipe may require zero or more
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arguments which are specific to the recipe. Here's an example which runs the
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`ExtractElements` recipe, which, as the same suggests, extracts out elements.
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This recipe expects one argument, which uses the [IFC Query
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syntax](https://wiki.osarch.org/index.php?title=IfcOpenShell_code_examples#IFC_Query_Syntax).
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This recipe expects one argument, which uses the `IFC Query
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syntax <https://wiki.osarch.org/index.php?title=IfcOpenShell_code_examples#IFC_Query_Syntax>`_.
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In this example, we'll extract out all `IfcWall` elements.
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::
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Reference in New Issue
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