无法将 cv_bridge 与 ROS Kinetic 和 Python3 一起使用

Question

我在 Ubuntu 14.04 上有一个使用 ROS indigo 和 python3 的计算机视觉项目，然后我不得不在 Ubuntu 16.04 上使用 ROS 动力学。在这里我遇到了多个问题：

1）我安装了opencv，但是在python3中无法导入，报错信息是：

Traceback (most recent call last):
  File "test.py", line 2, in <module>
    import cv2
ImportError: /opt/ros/kinetic/lib/python2.7/dist-packages/cv2.so: 
undefined symbol: PyCObject_Type

我发现只是重命名 cv2.so

cd /opt/ros/kinetic/lib/python2.7/dist-packages/
sudo mv cv2.so cv2_ros.so

然后我就可以导入 cv2 并使用它了

2）然后我无法导入rospy，但是安装python3-catkin-pkg-modules和python3-rospkg-modules解决了这个问题

3) 最后我遇到了一个关于 cv_bridge 的问题，它说：

[ERROR] [1520780674.845066]: bad callback: <bound method ViewsBuffer.update of <__main__.ViewsBuffer object at 0x7f5f45a07f28>>
Traceback (most recent call last):
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/topics.py", line 750, in _invoke_callback
    cb(msg)
  File "test.py", line 48, in update
    im = self.bridge.imgmsg_to_cv2(im, "bgr8")
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/cv_bridge/core.py", line 163, in imgmsg_to_cv2
    dtype, n_channels = self.encoding_to_dtype_with_channels(img_msg.encoding)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/cv_bridge/core.py", line 99, in encoding_to_dtype_with_channels
    return self.cvtype2_to_dtype_with_channels(self.encoding_to_cvtype2(encoding))
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/cv_bridge/core.py", line 91, in encoding_to_cvtype2
    from cv_bridge.boost.cv_bridge_boost import getCvType
ImportError: dynamic module does not define module export function (PyInit_cv_bridge_boost)

我相信问题出在 cv_bridge_boost.so 文件中。 我还尝试从https://github.com/ros-perception/vision_opencv 构建 cv_bridge，但它会自动为 python2.7 构建，我试图稍微修改 CMakeLists.txt 以在其中指定 python3，但我对 CMakeLists 没有太多经验，所以它没有不行。我还尝试将 cv_bridge 模块复制到我的项目文件夹，但它并没有太大变化，它仍然指向那个 cv_bridge_boost.so 文件。 还有一点要提的是 cv_bridge 在 python2.7 上运行良好，但我的项目需要 python3.5。

Answer 1

你是对的，你应该用python3构建cv_bridge。

你可以通过传递来做到这一点

-DPYTHON_EXECUTABLE=/usr/bin/python3 -DPYTHON_INCLUDE_DIR=/usr/include/python3.5m -DPYTHON_LIBRARY=/usr/lib/x86_64-linux-gnu/libpython3.5m.so

参数到 cmake。 或者，如果您使用 catkin 构建包，则可以执行以下步骤：

# `python-catkin-tools` is needed for catkin tool
# `python3-dev` and `python3-catkin-pkg-modules` is needed to build cv_bridge
# `python3-numpy` and `python3-yaml` is cv_bridge dependencies
# `ros-kinetic-cv-bridge` is needed to install a lot of cv_bridge deps. Probaply you already have it installed.
sudo apt-get install python-catkin-tools python3-dev python3-catkin-pkg-modules python3-numpy python3-yaml ros-kinetic-cv-bridge
# Create catkin workspace
mkdir catkin_workspace
cd catkin_workspace
catkin init
# Instruct catkin to set cmake variables
catkin config -DPYTHON_EXECUTABLE=/usr/bin/python3 -DPYTHON_INCLUDE_DIR=/usr/include/python3.5m -DPYTHON_LIBRARY=/usr/lib/x86_64-linux-gnu/libpython3.5m.so
# Instruct catkin to install built packages into install place. It is $CATKIN_WORKSPACE/install folder
catkin config --install
# Clone cv_bridge src
git clone https://github.com/ros-perception/vision_opencv.git src/vision_opencv
# Find version of cv_bridge in your repository
apt-cache show ros-kinetic-cv-bridge | grep Version
    Version: 1.12.8-0xenial-20180416-143935-0800
# Checkout right version in git repo. In our case it is 1.12.8
cd src/vision_opencv/
git checkout 1.12.8
cd ../../
# Build
catkin build cv_bridge
# Extend environment with new package
source install/setup.bash --extend

和

$ python3

Python 3.5.2 (default, Nov 23 2017, 16:37:01) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from cv_bridge.boost.cv_bridge_boost import getCvType
>>> 

如果遇到下一个错误

CMake Error at /usr/share/cmake-3.5/Modules/FindBoost.cmake:1677 (message):
  Unable to find the requested Boost libraries.

  Boost version: 1.58.0

  Boost include path: /usr/include

  Could not find the following Boost libraries:

          boost_python3

  No Boost libraries were found.  You may need to set BOOST_LIBRARYDIR to the
  directory containing Boost libraries or BOOST_ROOT to the location of
  Boost.
Call Stack (most recent call first):
  CMakeLists.txt:11 (find_package)

这是因为CMake试图找到libboost_python3.so库，但是在ubuntu中是libboost_python-py35.so(/usr/lib/x86_64-linux-gnu/libboost_python-py35.so)，所以你应该换行

find_package(Boost REQUIRED python3)

到

find_package(Boost REQUIRED python-py35)

在文件src/vision_opencv/cv_bridge/CMakeLists.txt 中并重建包。

Answer 2

我的系统中安装了 anaconda3，在使用 cv_bridge 时遇到了类似的问题。当我尝试使用catkin build cv_bridge 构建时，它会引发错误。我使用来自 conda 的 python3.7。我的 catkin cofig 命令是：

catkin config -DPYTHON_EXECUTABLE=/home/akashbaskaran/anaconda3/bin/python3 -DPYTHON_INCLUDE_DIR=/home/akashbaskaran/anaconda3/include/python3.7m -DPYTHON_LIBRARY=/home/akashbaskaran/anaconda3/lib/libpython3.7m.so

解决方案： 我做了几件事，问题得到了解决。

• 由于使用 anaconda，可执行文件和包含目录应该是您当前虚拟环境中的目录。 -DPYTHON_EXECUTABLE=/home/akashbaskaran/anaconda3/envs/tf/bin/python3.6 -DPYTHON_INCLUDE_DIR=/home/akashbaskaran/anaconda3/envs/tf/include/python3.6m -DPYTHON_LIBRARY=/home/akashbaskaran/anaconda3/envs/tf/lib/libpython3.6m.so e
• 我在尝试 catkin build cv_bridge 时遇到了构建问题。如果您遇到类似问题，请删除除 src 之外的所有文件夹。然后从终端运行 catkin_make（确保你在 catkin_workspace 中）。
• 获取当前工作空间source devel/setup.bash

现在 import cv2 from cv_bridge.boost.cv_bridge_boost import getCvType

应该可以正常工作。