遇到报错不要着急用字眼百度答案，报错中给的提示是最重要的。
在百度中折腾好几个小时，还因为用conda安装proj4，把本来好好的环境变量变得面目全非，source ~/.bahrc也不管用。最后认认真真看了报错，发现只需要设置好PKG_CONFIG_PATH就可以了。
# 先设置PKG_CONFIG_PATH环境变量
# 对应proj.pc所在路径
export PKG_CONFIG_PATH=/home/lucky/anaconda3_202105/lib/pkgconfig/:$PKG_CONFIG_PATH
# 然后重新运行安装命令 install.packages('proj4')
# 再运行 install.packages('ggalt') 即可
# 以下是安装proj4时候的报错
> install.packages('proj4')
trying URL 'https://mirrors.bfsu.edu.cn/CRAN/src/contrib/proj4_1.0-12.tar.gz'
Content type 'application/octet-stream' length 42887 bytes (41 KB)
==================================================
downloaded 41 KB
* installing *source* package ‘proj4’ ...
** package ‘proj4’ successfully unpacked and MD5 sums checked
** using staged installation
checking whether pkg-config knows about proj... no
checking whether the C++ compiler works... yes
checking for C++ compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether the compiler supports GNU C++... yes
checking whether x86_64-conda-linux-gnu-c++ -std=gnu++14 accepts -g... yes
checking for x86_64-conda-linux-gnu-c++ -std=gnu++14 option to enable C++11 features... none needed
checking for stdio.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for strings.h... yes
checking for sys/stat.h... yes
checking for sys/types.h... yes
checking for unistd.h... yes
checking for proj_api.h... no
checking with ACCEPT_USE_OF_DEPRECATED_PROJ_API_H...
checking for proj_api.h... no
checking for proj.h... no
checking for proj_get_source_crs in -lproj... no
configure: Retrying with pkg-config --static
Package proj was not found in the pkg-config search path.
Perhaps you should add the directory containing `proj.pc'
to the PKG_CONFIG_PATH environment variable
No package 'proj' found
checking for proj_get_source_crs in -lproj... no
configure: PROJ4 API available: no
configure: PROJ6 API available: no
checking whether to require PROJ6 API... no
configure: error: Cannot find working proj.h headers and library.
*** You may need to install libproj-dev or similar! ***
ERROR: configuration failed for package ‘proj4’
* removing ‘/home/lucky/anaconda3_202105/envs/R4.1.1/lib/R/library/proj4’
The downloaded source packages are in
‘/tmp/RtmpSVjnRX/downloaded_packages’
Updating HTML index of packages in '.Library'
Making 'packages.html' ... done
Warning message:
In install.packages("proj4") :
installation of package ‘proj4’ had non-zero exit status
还需要赶快恢复下原来的环境变量设置~~~
