* installing *source* package ‘proj4’ ...
** package ‘proj4’ successfully unpacked and MD5 sums checked
** using staged installation
checking for gcc... clang -arch arm64
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 we are using the GNU C compiler... yes
checking whether clang -arch arm64 accepts -g... yes
checking for clang -arch arm64 option to accept ISO C89... none needed
checking how to run the C preprocessor... clang -arch arm64 -E
checking for grep that handles long lines and -e... /usr/bin/grep
checking for egrep... /usr/bin/grep -E
checking for ANSI C header files... rm: conftest.dSYM: is a directory
rm: conftest.dSYM: is a directory
yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking proj_api.h usability... no
checking proj_api.h presence... no
checking for proj_api.h... no
checking with ACCEPT_USE_OF_DEPRECATED_PROJ_API_H... 
checking proj_api.h usability... yes
checking proj_api.h presence... yes
checking for proj_api.h... yes
checking whether we are using the GNU C++ compiler... yes
checking whether clang++ -arch arm64 -std=gnu++14 accepts -g... yes
checking for pj_init_plus in -lproj... no
checking for proj_create_crs_to_crs in -lproj... no
checking whether to require PROJ6 API... no
checking whether to use PROJ6 API... yes
configure: error: libproj and/or proj.h/proj_api.h not found in standard search locations.

*** Install PROJ library and if necessary set PKG_CPPFLAGS/PKG_LIBS accordingly.
ERROR: configuration failed for package ‘proj4’
* removing ‘/Volumes/Builds/packages/big-sur-arm64/results/4.1/proj4.Rcheck/proj4’