Added/improved description of scripted diagrams (#243)

doc/howtos/using_scripted_diagrams/using_scripted_diagrams.md

@@ -18,6 +18,10 @@ You can use multiple scripted diagrams at the same time, which will be stacked v
 
 The concept of scripted diagrams builds upon [scripted elements](../scripted_elements/scripted_elements_introduction.md) and [services](../using_services/using_services.md). [Tokens on scripted elements](../scripted_elements/tokens_on_scripted_elements.md) are used to convey data to the diagram service.
 
+![Scripted diagrams relations](assets/scripted_diagrams_relations.png)
+
+Each diagram service combines data from one or more scripted elements to create a single scripted diagram.
+
 ## Usage
 
 ### 1. Create or modify scripted elements to contribute data to a scripted diagram
@@ -52,6 +56,28 @@ See <a href="../using_services/using_services.html#service-definition">Using ser
 * The service function name must be the same as set in the scripted elements' `"ude_diagram_service"` parameter.
 ```
 
+#### Diagram service function description
+
+The scripted diagram's service function implementation must adhere to the following interface description:
+
+```{py:function} <function name>(view, element_data): str
+
+Create an SVG diagram based on scripted elements' context data 
+:param dict view: ZEISS INSPECT 'Inspection Details' canvas properties
+                  - 'width': (int) Canvas width in pixels 
+                  - 'height': (int) Canvas height in pixels
+                  - 'dpi': (float) Canvas resolution in dpi
+                  - 'font': (int) Default font size in pt
+:param list[dict1, dict2, ..., dictN] element_data: List of dictionaries containing scripted element references and context data 
+                                - 'element': (object) Element reference
+                                - 'data': (dict) Context data of the scripted element
+                                - 'type': (str) Element type (always 'SVGDiagram')
+:return: SVG diagram
+:rtype: str
+```
+
+#### Template
+
 The following script serves as a minimum template for a scripted diagram service:
 ```{code-block} python
 :caption: Scripted diagram service template
@@ -69,15 +95,15 @@ def diagram_service_template(view, element_data)->str:
     mpltools.setup_plot(plt, view)
 
     for e in element_data:
-        # Read the the current element 
+        # Read element reference 
         element = e['element']
         
-        # Read all parameters received from mapped scripted element
+        # Read scripted element's context data
         data = e['data']
 
         # Create your diagram
         # Example: 
-        # plt.plot ([element.name], [data['ude_diagram_radius']], 'bx')
+        plt.plot ([element.name], [data['ude_diagram_radius']], 'bx')
     
     return mpltools.create_svg(plt, view)