1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
|
.. _tut_lwpolyline:
Tutorial for LWPolyline
=======================
The :class:`~ezdxf.entities.LWPolyline` is defined as a single graphic entity,
which differs from the old-style :class:`~ezdxf.entities.Polyline` entity, which
is defined as a group of sub-entities.
:class:`~ezdxf.entities.LWPolyline` display faster (in AutoCAD) and consume
less disk space, it is a planar element, therefore all points in
:ref:`OCS` as ``(x, y)`` tuples (:attr:`LWPolyline.dxf.elevation` is the
z-axis value).
Create a simple polyline:
.. code-block:: python
import ezdxf
doc = ezdxf.new("R2000")
msp = doc.modelspace()
points = [(0, 0), (3, 0), (6, 3), (6, 6)]
msp.add_lwpolyline(points)
doc.saveas("lwpolyline1.dxf")
Append multiple points to a polyline:
.. code-block:: python
doc = ezdxf.readfile("lwpolyline1.dxf")
msp = doc.modelspace()
line = msp.query("LWPOLYLINE").first
if line is not None:
line.append_points([(8, 7), (10, 7)])
doc.saveas("lwpolyline2.dxf")
The LWPOLYLINE entity always returns polyline points as 5-tuple
(x, y, start_width, end_width, bulge), the start_width, end_width and
bulge values are 0 if not present:
.. code-block:: python
first_point = line[0]
x, y, start_width, end_width, bulge = first_point
Use the method :meth:`~ezdxf.entities.LWPolyline.points` as context manager to
edit polyline points, this method was introduced because accessing single points
was very slow in early versions of *ezdxf*, but now direct access by the index
operator ``[]`` is very fast and using the context manager is not required
anymore.
The advantage of the context manager is the ability to use a user defined point
format:
.. code-block:: python
doc = ezdxf.readfile("lwpolyline2.dxf")
msp = doc.modelspace()
line = msp.query("LWPOLYLINE").first
with line.points("xyseb") as points:
# points is a standard Python list
# existing points are 5-tuples, but new points can be
# set as (x, y, [start_width, [end_width, [bulge]]]) tuple
# set start_width, end_width to 0 to be ignored (x, y, 0, 0, bulge).
# delete last 2 points
del points[-2:]
# adding two points
points.extend([(4, 7), (0, 7)])
doc.saveas("lwpolyline3.dxf")
Each line segment can have a different start- and end-width, if omitted start-
and end-width is 0:
.. code-block:: python
doc = ezdxf.new("R2000")
msp = doc.modelspace()
# point format = (x, y, [start_width, [end_width, [bulge]]])
# set start_width, end_width to 0 to be ignored (x, y, 0, 0, bulge).
points = [(0, 0, .1, .15), (3, 0, .2, .25), (6, 3, .3, .35), (6, 6)]
msp.add_lwpolyline(points)
doc.saveas("lwpolyline4.dxf")
The first point carries the start- and end-width of the first segment, the
second point of the second segment and so on, the start- and end-width value
of the last point is used for the closing segment if the polyline is closed
else these values are ignored.
Start- and end-width only works if the DXF attribute :attr:`dxf.const_width` is
unset, to be sure delete it:
.. code-block:: python
# no exception will be raised if const_width is already unset:
del line.dxf.const_width
:class:`LWPolyline` can also have curved elements, they are defined by the
:ref:`bulge value`:
.. code-block:: python
doc = ezdxf.new("R2000")
msp = doc.modelspace()
# point format = (x, y, [start_width, [end_width, [bulge]]])
# set start_width, end_width to 0 to be ignored (x, y, 0, 0, bulge).
points = [(0, 0, 0, .05), (3, 0, .1, .2, -.5), (6, 0, .1, .05), (9, 0)]
msp.add_lwpolyline(points)
doc.saveas("lwpolyline5.dxf")
.. image:: gfx/LWPolyline5.PNG
The curved segment is drawn from the point which defines the *bulge* value to
the following point, the curved segment is always an arc. The bulge value
defines the ratio of the arc sagitta (segment height `h`) to half line segment
length (point distance), a bulge value of 1 defines a semicircle.
The curve is on the right side of the line for a bulge value > 0, and on the
left side of the line for a bulge value < 0.
The user defined point format, default is ``xyseb``:
- ``x`` = x coordinate
- ``y`` = y coordinate
- ``s`` = start width
- ``e`` = end width
- ``b`` = bulge value
- ``v`` = (x, y) as tuple
.. code-block:: python
msp.add_lwpolyline([(0, 0, 0), (10, 0, 1), (20, 0, 0)], format="xyb")
msp.add_lwpolyline([(0, 10, 0), (10, 10, .5), (20, 10, 0)], format="xyb")
.. image:: gfx/bulge.png
|
