PySDF (python-sdformat)

PySDF是一套为SDFormat XML提供的Python绑定。其理念是提供一个感觉上与XML一样快（或更快）的方法来处理SDF，同时增加了语法高亮、自动完成、验证和一些程度的验证。

当前的绑定可以从任何版本读取SDF并将其解析成通用表示。默认情况下，修改不会被验证或验证，这提供了更多的灵活性，但将来会添加可选的验证和验证方法。

安装

pip install python-sdformat

使用

绑定的元素根据官方SDF规范分组，但有少数例外。这意味着您可以通过遵循规范的嵌套来找到您需要的项目，例如，/sensor/imu/angular_velocity/x元素对应于类pysdf.Sensor.Imu.AngularVelocity.X，在SDF内部可以访问为parsed_sensor.imu.angular_velocity.x。此之前提到的例外是

• 绑定使用snake_case作为变量名，使用CamelCase作为类名
• 如果一个元素可能在父元素内部出现多次，其相应的属性将是一个元组，其名称将是复数，例如world.models[idx]。
• 元素Pose、Frame、Plugin和Include在多个元素中频繁出现，并被提升到顶级，即您将使用pysdf.Pose而不是pysdf.Model.Pose。

示例

基本读取和写入

from pysdf import SDF

sample_sdf = """<?xml version="1.0" ?>
<sdf version="1.6">
    <model name="empty_axis">
        <link name="link1" />
        <link name="link2" />
        <joint name="joint" type="fixed">
        <parent>link1</parent>
        <child>link2</child>
        <axis/>
        </joint>
    </model>
</sdf>
"""

# string round-trip
parsed = SDF.from_xml(sample_sdf)
sdf_string = parsed.to_xml()

# file round-trip
parsed.to_file("sample.sdf")
parsed = SDF.from_file("sample.sdf")

# prettify/reformat SDF to have nice indentation
parsed = SDF.from_file("sample.sdf", remove_blank_text=True)
parsed.to_file("sample.sdf", pretty_print=True)

手动构建SDF

from pysdf import SDF, Link, Joint, Model

reference_sdf = """
<sdf version="1.6">
    <model name="empty_axis">
        <link name="link1" />
        <link name="link2" />
        <joint name="joint" type="fixed">
            <parent>link1</parent>
            <child>link2</child>
        </joint>
    </model>
</sdf>
"""

element = SDF(
    Model(
        Link(name="link1"),
        Link(name="link2"),
        Joint(
            Joint.Parent(text="link1"),
            Joint.Child(text="link2"),
            # attributes are set at the end
            # because python only accepts kwargs at the end.
            name="joint",
            type="fixed",
        ),
        name="empty_axis",
    ),
    version="1.6",
)

element.to_file("sample.sdf", pretty_print=True)

基本修改

from pysdf import Link, State, Model, Link

# Complex elements (with own children) are added on first read
element = Link()
element.to_xml()  # "<link/>"
element.inertial
element.to_xml()  # "<link><inertial/></link>"

# Simple elements (basic types) are added on first write (__set__):
element.inertial.mass
element.to_xml()  # "<link><inertial/></link>"
element.inertial.mass = 5.0
element.to_xml() 
# "<link><inertial><mass>5.0</mass></inertial></link>"

# default values are populated where applicable
assert element.inertial.inertia.ixx == 1.0

# Where possible types are converted automatically
element = State.Model()
element.scale  # (1.0, 1.0, 1.0), tuple
element.scale = "1 2 3"
assert element.scale == (1.0, 2.0, 3.0)
element.scale = [5, 5, 5]
assert element.scale == (5.0, 5.0, 5.0)

# Inserting children works from sequences of kwargs
element = Model()
element.add(Link(name="test"))
element.add(Link(name="test2"), Link(name="test3"))
element.to_xml() 
# '<model><link name="test"/><link name="test2"/><link name="test3"/><pose/></model>'

完整修改示例

from pysdf import SDF, Link

sample_sdf = """<?xml version="1.0" ?>
<sdf version="1.6">
    <model name="empty_axis">
        <link name="link1" />
        <link name="link2" />
        <joint name="joint" type="fixed">
            <parent>link1</parent>
            <child>link2</child>
        </joint>
    </model>
</sdf>
"""

parsed = SDF.from_xml(sample_sdf, remove_blank_text=True)
model = parsed.model

model.name = "modified_model"
model.links[1].add(Link.ParticleEmitter(
    Link.ParticleEmitter.Emitting(text="true"),
    name="my_emitter",
    type="box"
))

parsed.to_file("sample.sdf", pretty_print=True)

迭代和过滤

您可以使用element.iter()递归地遍历子树（广度优先）的所有子元素。iter()还接受一个filter关键字参数，允许您仅返回从调用者到子元素具有所需路径的子元素。筛选器匹配路径的尾部，路径元素由/字符分隔，任何SDF标签都是有效的路径元素。这允许轻松选择和批量编辑特定的子元素，例如，使用filter="pose"选择SDF中的所有姿态元素，或者使用filter="model/pose"选择所有直接属于模型的姿态元素（模型的姿态）。

对于这个长的SDF示例，我想展示一些更实际的例子。

from pysdf import SDF
import numpy as np

# taken from: 
# https://github.com/ignitionrobotics/sdformat/blob/sdf12/test/sdf/joint_nested_parent_child.sdf
large_example = """
<sdf version="1.8">
  <model name="joint_nested_parent_child">
    <model name="M1">
      <link name="L1">
        <pose>0 0 1 0 0 0</pose>
      </link>
      <link name="L2">
        <pose>1 1 0 0 0 0</pose>
      </link>
      <frame name="F1">
        <pose>1 0 0 0 0 0</pose>
      </frame>
      <model name="M2">
        <pose>0 0 1 1.570796326790 0 0</pose>
        <link name="L1"/>
      </model>
    </model>

    <link name="L1">
      <pose>0 0 10 0 1.57079632679 0</pose>
    </link>

    <frame name="F1" attached_to="M1::L1">
      <pose>1 0 0 0 0 0</pose>
    </frame>

    <!-- Joint with a parent link in a nested model -->
    <joint name="J1" type="fixed">
      <pose>1 0 0 0 0 0</pose>
      <parent>M1::L1</parent>
      <child>L1</child>
    </joint>
    <!-- Joint with a sibling parent frame which is attached to a link in a nested model -->
    <joint name="J2" type="fixed">
      <pose>0 1 0 0 0 0</pose>
      <parent>F1</parent>
      <child>L1</child>
    </joint>
    <!-- Joint with a child link in a nested model -->
    <joint name="J3" type="fixed">
      <pose>0 0 1 0 0 0</pose>
      <parent>L1</parent>
      <child>M1::L2</child>
    </joint>

    <!-- Joint with a child frame in a nested model -->
    <joint name="J4" type="fixed">
      <pose>0 0 1 0 0 0</pose>
      <parent>L1</parent>
      <child>M1::F1</child>
    </joint>

    <!-- Joint with a child model in a nested model -->
    <joint name="J5" type="fixed">
      <pose>0 0 1 0 0 0</pose>
      <parent>L1</parent>
      <child>M1::M2</child>
    </joint>

    <!-- Joint with a nested model frame as a parent  -->
    <joint name="J6" type="fixed">
      <pose>0 0 1 0 0 0</pose>
      <parent>M1::__model__</parent>
      <child>L1</child>
    </joint>

    <!-- Joint with a nested model frame as a child  -->
    <joint name="J7" type="fixed">
      <pose>0 0 1 0 0 0</pose>
      <parent>L1</parent>
      <child>M1::__model__</child>
    </joint>
  </model>
</sdf>
"""

# remove_blank_text strips whitespace to allow neat formatting
# later on
element = SDF.from_xml(large_example, remove_blank_text=True)
element.version = "1.9"  # v1.9 supports pose/@degrees

# convert all poses to degrees
for pose in element.iter("pose"):
    pose.degrees = True
    pose_ndarray = np.fromstring(pose.text, count=6, sep=" ")
    rotation_rad = pose_ndarray[3:]
    rotation_deg = rotation_rad / (2*np.pi) * 360
    pose_ndarray[3:] = rotation_deg
    pose.text = " ".join(map(str, pose_ndarray))

# turn on self-collision for all links in the nested model
for link in element.iter("model/model/link"):
    link.self_collide = True

# turn self-collision off (using a different syntax)
for link in element.model.iter("link"):
    link.self_collide = False

# offset all links by some vector
for pose in element.iter("link/pose"):
    pose_ndarray = np.fromstring(pose.text, count=6, sep=" ")
    pose_ndarray[:3] += (0, 0, 1)
    pose.text = " ".join(map(str, pose_ndarray))

element.to_file("sample.sdf", pretty_print=True)