Pangolin库是在SLAM学习中常用的库之一，因为我在编译ORB-SLAM2过程中，一直报下面这样的错：
Build type: Release
-- Using flag -std=c++11.
-- Using opencv version 3.4.5
CMake Error at CMakeLists.txt:48 (find_package):
Found package configuration file:
/usr/local/lib/cmake/Pangolin/PangolinConfig.cmake
but it set Pangolin_FOUND to FALSE so package "Pangolin" is considered to
be NOT FOUND. Reason given by package:
Pangolin could not be found because dependency Eigen3 could not be found.
-- Configuring incomplete, errors occurred!
See also "/home/dzh/slambook/EAO-SLAM/build/CMakeFiles/CMakeOutput.log".
See also "/home/dzh/slambook/EAO-SLAM/build/CMakeFiles/CMakeError.log".
上网查询十几个链接后，发现不是Eigen3的问题，而是Pangolin版本的问题，所以需要卸载重装。因为pangolin是通过源代码安装的，所以下面步骤适用于所有源代码安装的库的卸载！
一、删除库和头文件
cd Pangolin/build
make clean
sudo make uninstall
执行之后就会开始卸载所有的.so文件和.h文件。
二、删除源代码
cd ../..
sudo rm -r Pangolin
执行之后删除源代码文件夹。
三、删除残留文件夹
更新下索引，搜索pangolin的位置
sudo updatedb
locate pangolin
可以看到在/usr/local/include/pangolin目录还未删除，因为第一步是卸载了该目录下的所有.h文件。
/usr/local/include/pangolin
/usr/local/include/pangolin/compat
/usr/local/include/pangolin/console
/usr/local/include/pangolin/display
/usr/local/include/pangolin/factory
/usr/local/include/pangolin/geometry
/usr/local/include/pangolin/gl
/usr/local/include/pangolin/handler
/usr/local/include/pangolin/image
/usr/local/include/pangolin/log
所以，我们将该目录删除即可。
sudo rm -r /usr/local/include/pangolin
四、检验卸载
再次搜索pangolin的位置
locate pangolin
发现只有在Trash中才能找到，卸载成功！
/home/dzh/.local/share/Trash/expunged/2600043745/build/include/pangolin
/home/dzh/.local/share/Trash/expunged/2600043745/build/include/pangolin/factory
/home/dzh/.local/share/Trash/expunged/2600043745/build/include/pangolin/factory/RegisterFactoriesVideoInterface.h
/home/dzh/.local/share/Trash/expunged/2600043745/build/include/pangolin/factory/RegisterFactoriesVideoOutputInterface.h
/home/dzh/.local/share/Trash/expunged/2600043745/build/include/pangolin/factory/RegisterFactoriesWindowInterface.h
五、重新安装
先到 stevenlovegrove /Pangolin 选择ORB-SLAM2对应的0.5版本，然后下载到本地。
然后跟随安装教程，包含编译错误解决：ubuntu18.04安装pangolin库，图文详解