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Upright
=======
.. module:: ezdxf.upright
The functions in this module can help to convert an inverted :ref:`OCS` defined
by an extrusion vector (0, 0, -1) into a :ref:`WCS` aligned OCS defined by
an extrusion vector (0, 0, 1).
This simplifies 2D entity processing for `ezdxf` users and creates DXF
output for 3rd party DXF libraries which ignore the existence of the :ref:`OCS`.
Supported DXF entities:
- CIRCLE
- ARC
- ELLIPSE (WCS entity, flips only the extrusion vector)
- SOLID
- TRACE
- LWPOLYLINE
- POLYLINE (only 2D entities)
- HATCH
- MPOLYGON
- INSERT (block references)
.. warning::
The WCS representation of OCS entities with flipped extrusion vector
is not 100% identical to the source entity, curve orientation and vertex order
may change, see `additional explanation`_ below.
A mirrored text represented by an extrusion vector (0, 0, -1)
cannot represented by an extrusion vector (0, 0, 1), therefore this CANNOT
work for text entities or entities including text:
TEXT, ATTRIB, ATTDEF, MTEXT, DIMENSION, LEADER, MLEADER
Usage
-----
The functions can be applied to any DXF entity without expecting errors or
exceptions if the DXF entity is not supported or the extrusion vector differs
from (0, 0, -1). This also means you can apply the functions multiple times to
the same entities without any problems. A common case would be to upright all
entities of the model space:
.. code-block:: Python
import ezdxf
from ezdxf.upright import upright_all
doc = ezdxf.readfile("your.dxf")
msp = doc.modelspace()
upright_all(msp)
# doing it again is no problem but also has no further effects
upright_all(msp)
Another use case is exploding block references (INSERT) which may include
reflections (= scaling by negative factors) that can lead to inverted
extrusion vectors.
.. code-block:: Python
for block_ref in msp.query("INSERT"):
entities = block_ref.explode() # -> EntityQuery object
upright_all(entities)
Functions
---------
.. autofunction:: upright
.. autofunction:: upright_all
Additional Explanation
----------------------
This example shows why the entities with an inverted OCS, extrusion vector is
(0, 0, -1), are not exact the same as with an WCS aligned OCS, extrusion vector
is (0, 0, 1).
.. note::
The ARC entity represents the curve **always** in counter-clockwise
orientation around the extrusion vector.
.. code-block:: Python
import ezdxf
from ezdxf.upright import upright
from ezdxf.math import Matrix44
doc = ezdxf.new()
msp = doc.modelspace()
arc = msp.add_arc(
(5, 0),
radius=5,
start_angle=-90,
end_angle=90,
dxfattribs={"color": ezdxf.const.RED},
)
# draw lines to the start- and end point of the ARC
msp.add_line((0, 0), arc.start_point, dxfattribs={"color": ezdxf.const.GREEN})
msp.add_line((0, 0), arc.end_point, dxfattribs={"color": ezdxf.const.BLUE})
# copy arc
mirrored_arc = arc.copy()
msp.add_entity(mirrored_arc)
# mirror copy
mirrored_arc.transform(Matrix44.scale(-1, 1, 1))
# This creates an inverted extrusion vector:
assert mirrored_arc.dxf.extrusion.isclose((0, 0, -1))
# draw lines to the start- and end point of the mirrored ARC
msp.add_line((0, 0), mirrored_arc.start_point, dxfattribs={"color": ezdxf.const.GREEN})
msp.add_line((0, 0), mirrored_arc.end_point, dxfattribs={"color": ezdxf.const.BLUE})
Result without applying the :func:`upright` function - true mirroring:
.. image:: gfx/upright_arc_0.png
:align: center
:width: 600px
.. code-block:: Python
...
# This creates an inverted extrusion vector:
assert mirrored_arc.dxf.extrusion.isclose((0, 0, -1))
start_point_inv = mirrored_arc.start_point
end_point_inv = mirrored_arc.end_point
upright(mirrored_arc)
# OCS is aligned with WCS:
assert mirrored_arc.dxf.extrusion.isclose((0, 0, 1))
# start- and end points are swapped after applying upright()
assert mirrored_arc.start_point.isclose(end_point_inv)
assert mirrored_arc.end_point.isclose(start_point_inv)
# draw lines to the start- and end point of the mirrored ARC
msp.add_line((0, 0), mirrored_arc.start_point, dxfattribs={"color": ezdxf.const.GREEN})
msp.add_line((0, 0), mirrored_arc.end_point, dxfattribs={"color": ezdxf.const.BLUE})
Result after applying the :func:`upright` function - false mirroring:
.. image:: gfx/upright_arc_1.png
:align: center
:width: 600px
To avoid this issue the ARC entity would have to represent the curve in clockwise
orientation around the extrusion vector (0, 0, 1), which is not possible!
.. note::
The shape of the mirrored arcs is the same for both extrusion vectors, but
the start- and the end points are swapped (reversed vertex order)!
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