Developer documentation updated

docs/source/developer/developer_documentation.rst

@@ -1,15 +1,143 @@
-************************************
+***********************
 Developer Documentation
-************************************
+***********************
+
+The following section provides detailed information on the the software architecture and on the possibilities to extend ESBO-ETC.
+The source code of ESBO-ETC and this documentation can be found on the `IRS Gitea-server <https://egit.irs.uni-stuttgart.de/esbo_ds/ESBO-ETC>`_.
+
+.. note::
+   In the following, methods of the source code may be mentioned without details on the required parameters or the return values. Please refer to the :ref:`api` for details.
 
-============================
 Project Structure
-============================
+=================
+
+This project is structured into several folders as shown below. The three main folders are ``docs``, which contains the documentation,
+``esbo_etc`` containing all source files and ``tests``, where all tests are located.
+
+::
+
+    root
+    ├── docs                        Documentation files
+    │   └── source                  Source files of the documentation
+    │       ├── configuration       Configuration chapter of the documentation
+    │       ├── developer           Developer chapter of the documentation
+    │       └── usage               Usage chapter of the documentation
+    ├── esbo_etc                    Source code of ESBO-ETC
+    │   ├── classes                 Contains all classes of the source code
+    │   │   ├── optical_component   Contains all class files of the optical components
+    │   │   ├── psf                 Contains all class files to model the different types of PSF
+    │   │   ├── sensor              Contains all class files of the sensors
+    │   │   └── target              Contains all class files of the targets
+    │   ├── lib                     Contains all library functions
+    │   └── esbo-etc.py             This is the main file to run the application
+    └──  tests                      Contains all tests
+        ├── data                    Necessary data for all tests
+        ├── optical_component       Tests of the optical components
+        ├── psf                     Tests of the different PSF implementations
+        ├── sensor                  Tests of all sensors
+        └── target                  Tests of all targets
+
+Software Architecture
+=====================
+
+For modelling the radiation transportation, the `decorator pattern <https://en.wikipedia.org/wiki/Decorator_pattern>`_ and the
+`factory method pattern <https://en.wikipedia.org/wiki/Factory_method_pattern>`_ were used as shown in the figure below.
+
+.. figure:: decorator_pattern.pdf
+   :alt: Decorator Pattern
+   :width: 100%
+
+   The decorator pattern used for the radiation transportation.
+
+The radiation transportation pipeline consists always of a single target emitting the signal radiation.
+This target may be encapsulated by multiple optical components which manipulate the radiation by either adding their own background radiation or by decreasing the transmitted radiation.
+The outermost part of the radiation transportation pipeline is formed by some kind of sensor component, detecting the radiation.
+The quality of the detected signal can then be determined by calculating the signal to noise ration (SNR).
+
+.. figure:: class_diagram.pdf
+   :alt: Class Diagram
+
+   Class diagram of the software architecture.
+
+Radiant Interface
+-----------------
+
+In order to implement the aforementioned radiation transportation pipeline, a sophisticated software architecture has been designed.
+As shown in the class diagram, the class ``IRadiant`` forms the backbone of the structure.
+This interface class defines the two methods ``calcSignal()`` and ``calcBackground()`` and therefore the basic layout of all decorated classes.
+All targets and optical components implement this interface in oder to allow the cascading calculation of the signal and background fluxes.
+For both targets and optical components exists an abstract superclass which implements the required interface. This allows the actual
+classes to focus on the initialization and calculation of their own properties, ignoring the implementation of the interface.
+
+
+
+Target
+------
+
+The abstract class ``ATarget`` implements the interface provided by ``IRadiant`` and provides the abstract method ``checkConfig()`` which is used to check the relevant parts of the configuration file for this component.
+All available target types must inherit from ``ATarget`` and therefore must implement the method ``checkConfig()``.
+As the superclass ``ATarget`` implements the interface provided by ``IRadiant``, the compatibility to the radiation transportation pipeline is ensured.
+All subclasses therefore only set up a ``SpectralQty``-object containing the emitted radiation and call the constructor of ``ATarget``.
+
+Optical Component
+-----------------
+
+The abstract class ``AOpticalComponent`` implements the interface provided by ``IRadiant`` and thereby the two methods ``calcSignal()`` and ``calcBackground()``.
+This includes the treatment of central obstruction of the components as well as transmittance / reflectance coefficients.
+Additionally, ``AOpticalComponent`` provides the two methods ``propagate()`` for handling the propagation of incoming radiation through the optical component and ``ownNoise()`` for calculating the background radiation contribution of this component.
+The two function may be overwritten by the subclasses, if a custom implementation is necessary.
+Otherwise, the parameters ``transreflectivity`` and ``noise`` of the constructor method will be used for the calculations.
+In order to check the relevant parts of the configuration file for this component, the class provides the abstract method ``checkConfig()`` which has to be implement by all subclasses.
+
+According to the restrictions above, subclasses of ``AOpticalComponent`` can be implemented in two possible ways: either by providing the parameters ``transreflectivity`` and ``noise`` to the constructor of the superclass or by implementing the two methods ``propagate()`` and ``ownNoise()``.
+
+Hot Optical Component
+^^^^^^^^^^^^^^^^^^^^^
+
+The abstract class ``AHotOpticalComponent`` extends the abstract superclass ``AOpticalComponent`` by implementing the method ``ownNoise()`` assuming grey body radiation in order to model optical components with a thermal background contribution.
+This has the consequence, that every subclass of ``AHotOpticalComponent`` must implement the method ``propagate()``, which handles to propagation of the signal and backgroudn radiation through the component.
+Like ``AOpticalComponent``, the class ``AHotOpticalComponent`` provides the abstract method ``checkConfig()`` for checking the configuration file.
+
+Sensor
+------
+
+
 
-============================
 Classes
-============================
+=======
+
+All spectral quantities used for calculations, e.g. spectral flux densities, spectral reflectances, etc., are handled as ``SpectralQty``-objects, which support operations like additions, substractions, multiplications, divisions, etc.
+Additionally, ESBO-ETC uses Astropy-units for all calculations in order to avoid any conversion errors.
+The class ``Entry`` is used to represent the tags of the XML-configuration file.
 
-============================
 Extending ESBO-ETC
-============================
+==================
+
+ESBO-ETC can be easily extended by adding new optical components or a new detector component.
+
+Adding Targets
+--------------
+
+
+
+Adding Optical Components
+-------------------------
+
+Extending ESBO-ETC by a new optical component consists of two tasks.
+
+First of all, the new optical component class has to be implemented in a separate file in the *classes*-folder.
+The new class must inherit from the abstract class ``AOpticalComponent`` or, in case of an optical component with thermal emission, from the abstract class ``AHotOpticalComponent`` and implement all abstract methods.
+In case of a cold optical component, the new class must implement the method ``checkConfig()`` and call the constructor of the super class.
+In case of a hot optical component, the new class must implement the method ``checkConfig()`` as well as the method ``propagate()`` and call the constructor of the super class.
+
+The method ``checkConfig()`` is used for checking the XML-configuration file and accepts as parameter the corresponding part of the configuration as ``Entry``-object.
+In case of an configuration error, the method must return the corresponding error message.
+
+The method ``propagate()`` is used to model the propagation of incoming radiation through the optical component.
+Therefore, this method receives as parameter the incoming radiation as ``SpectralQty``-object and must return the manipulated radiation as ``SpectralQty``-object.
+
+The second task consists of 
+
+Adding Detector Components
+--------------------------
+