ubuntu20.04 ROS catkin

报错一：
错误提示：

 Running command: "cmake /home/zzw/catkin_ws/src -DCATKIN_DEVEL_PREFIX=/home/zzw/catkin_ws/devel -DCMAKE_INSTALL_PREFIX=/home/zzw/catkin_ws/install -G Unix Makefiles" in "/home/zzw/catkin_ws/build"
####
-- Using CATKIN_DEVEL_PREFIX: /home/zzw/catkin_ws/devel
-- Using CMAKE_PREFIX_PATH: /opt/ros/noetic
-- This workspace overlays: /opt/ros/noetic
-- Using PYTHON_EXECUTABLE: /home/zzw/anaconda3/bin/python3
-- Using Debian Python package layout
-- Could NOT find PY_em (missing: PY_EM) 
CMake Error at /opt/ros/noetic/share/catkin/cmake/empy.cmake:30 (message):
  Unable to find either executable 'empy' or Python module 'em'...  try
  installing the package 'python3-empy'
Call Stack (most recent call first):
  /opt/ros/noetic/share/catkin/cmake/all.cmake:164 (include)
  /opt/ros/noetic/share/catkin/cmake/catkinConfig.cmake:20 (include)
  CMakeLists.txt:58 (find_package)


-- Configuring incomplete, errors occurred!
See also "/home/zzw/catkin_ws/build/CMakeFiles/CMakeOutput.log".
Invoking "cmake" failed

ubuntu20.04，在catkin_make的时候报错
解决方案：
1、用conda list 看看你有没有安装 empy，没有装的话就要在conda里面安装它，conda install -c conda-forge empy
2、还有个方法就是不用anaconda的Python环境，把.bashrc里面的 export PATH="/home/用户名/anaconda3/bin:$PATH" 注释掉，再source一下

报错二：
错误提示：

ImportError: "from catkin_pkg.package import parse_package" failed: No module named 'catkin_pkg'
Make sure that you have installed "catkin_pkg", it is up to date and on the PYTHONPATH.
CMake Error at /opt/ros/noetic/share/catkin/cmake/safe_execute_process.cmake:11 (message):
  execute_process(/home/zzw/anaconda3/bin/python3
  "/opt/ros/noetic/share/catkin/cmake/parse_package_xml.py"
  "/opt/ros/noetic/share/catkin/cmake/../package.xml"
  "/home/zzw/catkin_ws/build/catkin/catkin_generated/version/package.cmake")
  returned error code 1
Call Stack (most recent call first):
  /opt/ros/noetic/share/catkin/cmake/catkin_package_xml.cmake:74 (safe_execute_process)
  /opt/ros/noetic/share/catkin/cmake/all.cmake:168 (_catkin_package_xml)
  /opt/ros/noetic/share/catkin/cmake/catkinConfig.cmake:20 (include)
  CMakeLists.txt:58 (find_package)


-- Configuring incomplete, errors occurred!
See also "/home/zzw/catkin_ws/build/CMakeFiles/CMakeOutput.log".
See also "/home/zzw/catkin_ws/build/CMakeFiles/CMakeError.log".
Invoking "cmake" failed

解决方案：

python3 -m pip install catkin_pkg