reader.md

@@ -11,7 +11,13 @@ Data is read in semi-asynchronously from the Listener thread on the client appli
 Reader child classes are put in the `Sensors` directory and the classes that are in that directory should be used as reference when creating a new sensor service.
 
 ### Creating the class
-To create a new function to send data to the HV Robot, the Writer class must be extended. the child class needs to have a `__init__()` function where the *subscriber* is defined and the probe name is passed to the parent constructor; and a `callback` function where the data is formatted to be passed to the robot over the probes. 
+
+To create a new function to read data from the HV Robot, the Reader class must be extended. the child class needs to have a `__init__()` function where the *publisher* is defined and saved to a class variable and the required 
+probes are defined and passed to the parent. the child class also requires a `publish` function that creates the message to be published to a ros topic. data from the robot is stored in the *queue* variable as a dictionary, where the key is the probe name. a reader class can get data from multiple (or a single) probe, but can only publish to a single ros topic
+
+### Extending a class to publish to multiple topics
+
+If there are more than one ros topic that requires the same data formatting, such as the IR cameras where there are 4 cameras and therefor 4 topics, there must be 4 classes. however a middle class can be created in the same form as above, however rather than specifying in the constructor the probes that are passed in, the constructor takes the probes as a input variable. then child classes can be created that contain only a constructor where the probes are defined and passed to their parent. Because the topic names in the publisher are defined by the probes, as long as the probes names are different in the child class it will create a unique topic for each instance.
 
 #### Formatting the data
 The writer will take either a list of messages or a single message. if you send a single message, and there is only a single probe associated with the class, then a single probe-message tuple is created, if there are multiple probes associated with this class, then each probe is sent the same message. If a message array is passed and there are multiple probes defined, then the two arrays will be zipped together, and if they are not the same length then it will raise an exception. messages are associated to probes sequentially, so data at index 0 is paired with probe at index 0.