anchor.diff:      elseif (trim(tag).eq.'-lon0') then
           i = i + 1
           call get_command_argument(i,tag)
  -        read(tag,*) lon0
  +        read(tag,*,err=9001) lon0
       elseif (trim(tag).eq.'-lat0') then
           i = i + 1
           call get_command_argument(i,tag)
  -        read(tag,*) lat0
  +        read(tag,*,err=9002) lat0
       elseif (trim(tag).eq.'-radius') then
           i = i + 1
           call get_command_argument(i,tag)
  -        read(tag,*) radius_sphere
  +        read(tag,*,err=9003) radius_sphere
   
       else
           call usage('stereo_project: no option '//trim(tag))
  
positive.code: enddo
  
  return
  end subroutine
  
  !--------------------------------------------------------------------------------------------------!
  
negative.code: 
  subroutine gcmdln()
  
  use io, only: stderr
  use earth, only: radius_earth_km
  
  use stereo_project, only: project_mode, &
  