How to include absolute path in C++

Question

Project Sturcture

I am learning how to build a C++/cmake template. The structure looks like:

.
├── CMakeLists.txt
├── README.md
└── src
    ├── CMakeLists.txt
    └── geometry
        ├── CMakeLists.txt
        └── line
            ├── CMakeLists.txt
            ├── line.cpp
            └── line.h

Every CMakeLists.txt looks like the following:

./CMakeLists.txt:

cmake_minimum_required(VERSION 3.20.0)
project(cmake_template VERSION 0.0.1 LANGUAGES CXX)

add_subdirectory(src)

./src/CMakeLists.txt:

add_subdirectory(geometry)

./src/geometry/CMakeLists.txt:

add_subdirectory(line)

./src/geometry/line/CMakeLists.txt:

add_library(line line.cpp)
target_include_directories(line PUBLIC .)

And the implementation looks like:

line.h:

#include <string>

class Line{
private:
    std::string name;
public:
    Line(std::string);
    virtual void display();
};

line.cpp:

#include "src/geometry/line/line.h"
#include <iostream>

Line::Line(std::string name):name(name){}

void Line::display(){
    std::cout << "A line with name " << this->name << "\n";
}

Compile and error

The command I run is cmake -S . -B build && cmake --build build/, and it shows the error:

[1/2] Building CXX object src/geometry/line/CMakeFiles/line.dir/line.cpp.o
FAILED: src/geometry/line/CMakeFiles/line.dir/line.cpp.o 
/usr/bin/clang++  -I../src/geometry/line/. -g -MD -MT src/geometry/line/CMakeFiles/line.dir/line.cpp.o -MF src/geometry/line/CMakeFiles/line.dir/line.cpp.o.d -o src/geometry/line/CMakeFiles/line.dir/line.cpp.o -c ../src/geometry/line/line.cpp
../src/geometry/line/line.cpp:1:10: fatal error: 'src/geometry/line/line.h' file not found
#include "src/geometry/line/line.h"
         ^~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
ninja: build stopped: subcommand failed.

The code can compile if I change to #include "line.h"

My questions are:

• How can I include the absolute path without change the current structure? I.e., I don't want to change CMakeLists.txt in the upper level, only ./src/geometry/line/CMakeLists.txt can be changed.
• How can I use <> to include the absolute path? I.e., #include <src/geometry/line/line.h>? The reason of using <> is from the Canonical CPP Project Structure.