Add fine_odometry.md

Signed-off-by: Gregory Mermet <g.mermet@ez-wheel.com>

Author: GMezWheel

fine_odometry.md

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+
+# Fine odometry function
+
+The function **getFineOdometry()** allows to retrieve a more precise position distance of the SWD Core at low level speed.
+
+> This position is non-safe. Safety relevant applications should rely with **getOdometryValue()**.
+
+This function use the precise multiturn position value (**hall_encoder**), in units of motor mechanical degrees.
+
+> The counter direction depends of the position polarity parameter.
+
+## COMMISSIONING
+In order to switch from **position_value** to **hall_encoder** data in the PDO mapping , the commissioning of the both motors have to be modifed as follow:
+```
+commissioning.py:
+
+    # TPDO3 communication mapping
+
+    # - statusword
+    # - position_value or hall_encoder
+
+    mapping = PDOMappingParameters()
+    mapping.nb = 2
+    mapping.items.append(0x6041_00_10)
+    # mapping.items.append(0x6064_00_20) # position_value
+    mapping.items.append(0x2305_06_20)  # hall_encoder
+
+    communication_client.setTPDOMappingParameters(PDOId.PDO_3, mapping)
+    check("setTPDOMappingParameters(PDOId.PDO_3)", error)
+ ```
+## ROS2
+The latest swd_diff_drive controller on github contains a parameter to indicate which odometry shall be used: `"fine_odometry": False.`By default, this parameter is set to false in order to continue using `position_value`data and `getOdometryValue()` function.
+
+## ROS1
+Until **getFineOdometry()** is available, a possible workaround is to modif "**nbPolePair**" setting into `configuration.json` file :
+	`"nbPolePair": 60.0` instead of `"nbPolePair": 5.0`
+
+Thus, the formula used by "**getOdometryValue**" will compute the same value as   "**getFineOdometryValue**" and all transparent to the swd_diff_drive_controller node.