Ubuntu20.04+ROS+VINS-Mono+VINS-Fusion解决catkin_make报错

由于ubuntu20.04自带的opencv版本为opencv4，而VINS所用的opencv版本为opencv3，在catkin_make🥌会有一堆报错，例如：

 对应解决方案：

1.

error: ‘CV_GRAY2RGB’ was not declared in this scope 

在报错的几个文件上添加头文件 #include <opencv2/imgproc/imgproc_c.h>

2.

error: ‘CV_CALIB_CB_ADAPTIVE_THRESH’ was not declared in this scope 、
error: ‘CV_CALIB_CB_NORMALIZE_IMAGE’ was not declared in this scope、
error: ‘CV_CALIB_CB_FILTER_QUADS’ was not declared in this scope 
error: ‘CV_CALIB_CB_FAST_CHECK’ was not declared in this scope
error: ‘CV_FONT_HERSHEY_SIMPLEX’ was not declared in this scope

将
CV_CALIB_CB_ADAPTIVE_THRESH、CV_CALIB_CB_NORMALIZE_IMAGE、
CV_CALIB_CB_FILTER_QUADS 、 CV_CALIB_CB_FAST_CHECK、
CV_FONT_HERSHEY_SIMPLEX
修改为 ：
cv::CALIB_CB_ADAPTIVE_THRESH 、 cv::CALIB_CB_NORMALIZE_IMAGE 、
cv::CALIB_CB_FILTER_QUADS 、 cv::CALIB_CB_FAST_CHECK
cv::FONT_HERSHEY_SIMPLEX

3.在解决VINS-Fusion报错时，遇到比较特殊的：

error: ‘CV_LOAD_IMAGE_GRAYSCALE’ was not declared in this scope

在改为cv::LOAD_IMAGE_GRAYSCALE时，仍出现报错：

error: ‘LOAD_IMAGE_GRAYSCALE’ is not a member of ‘cv’

是因为CV_LOAD_IMAGE_GRAYSCALE变量名改为了：cv::IMREAD_GRAYSCALE，不要改成别的。