Minor README polish

README.md

@@ -99,14 +99,13 @@ Both AR-Drone 1.0 and 2.0 are equipped with two cameras. One frontal camera poin
 
 * The way that the other two streams work depend on the type of Drone.
 
-        * Drone 1
+    * Drone 1
 
-        Drone 1 supports four modes of video streams: Front camera only, bottom camera only, front camera with bottom camera inside (picture in picture) and bottom camera with front camera inside (picture in picture). According to active configuration mode, the driver decomposes the PIP stream and publishes pure front/bottom streams to corresponding topics. The `camera_info` topic will include the correct image size.
+    Drone 1 supports four modes of video streams: Front camera only, bottom camera only, front camera with bottom camera inside (picture in picture) and bottom camera with front camera inside (picture in picture). According to active configuration mode, the driver decomposes the PIP stream and publishes pure front/bottom streams to corresponding topics. The `camera_info` topic will include the correct image size.
 
-        * Drone 2
-
-        Drone 2 does not support PIP feature anymore, therefore only one of `ardrone/front` or `ardrone/bottom` topics will be updated based on which camera is selected at the time.
+    * Drone 2
 
+    Drone 2 does not support PIP feature anymore, therefore only one of `ardrone/front` or `ardrone/bottom` topics will be updated based on which camera is selected at the time.
 
 ### Tag Detection
 
@@ -141,7 +140,7 @@ The range for each component should be between -1.0 and 1.0. The maximum range c
 
 ## Coordinate Frames
 
-The driver publishes two [`tf`](***) transforms between three reference frames: `${tf_prefix}/${base_prefix}_link`, `${tf_prefix}/${base_prefix}_frontcam` and `${tf_prefix}/${base_prefix}_bottomcam`. The `${tf_prefix}` is ROS standard way to handle multi-robot `tf` trees and can be set using `tf_prefix` parameters, by default it is empty. The ${base_link} is the shared name prefix of all three reference frames and can also be set using parameters, by default it has the value of `ardrone_base`. Using default parameters, the three frames would be: `ardrone_base_link`, `ardrone_base_frontcam` and `ardrone_base_bottomcam`. By default the root frame is  `ardrone_base_link`. Therefor `ardrone_base_frontcam` and `ardrone_base_bottomcam` are children of `ardrone_base_link` in the published `tf` tree. This can be changed using `root_frame` parameter.
+The driver publishes two [`tf`](http://www.ros.org/wiki/tf) transforms between three reference frames: `${tf_prefix}/${base_prefix}_link`, `${tf_prefix}/${base_prefix}_frontcam` and `${tf_prefix}/${base_prefix}_bottomcam`. The `${tf_prefix}` is ROS standard way to handle multi-robot `tf` trees and can be set using `tf_prefix` parameters, by default it is empty. The `${base_link}` is the shared name prefix of all three reference frames and can also be set using parameters, by default it has the value of `ardrone_base`. Using default parameters, the three frames would be: `ardrone_base_link`, `ardrone_base_frontcam` and `ardrone_base_bottomcam`. By default the root frame is  `ardrone_base_link`. Therefor `ardrone_base_frontcam` and `ardrone_base_bottomcam` are children of `ardrone_base_link` in the published `tf` tree. This can be changed using `root_frame` parameter.
 
 The `frame_id` field in header of all published topics (navdata, imu, cameras) will have the appropriate frame names. All frames are [ROS REP 103](http://www.ros.org/reps/rep-0103.html) compatible.
 
@@ -269,7 +268,7 @@ rosrun camera_calibration cameracalibrator.py --size [SIZE] --square [SQUARESIZE
 
 After successful calibration, press the `commit` button in the UI. The driver will receive the data from the camera calibration node, then will save the information by default in `~/.ros/camera_info/ardrone_front.yaml`. From this point on, whenever you run the driver on the same computer this file will be loaded automatically by the driver and its information will be published to appropriate `camera_info` topic. Sample calibration files for AR-Drone 2.0's cameras are provided in `data/camera_info` folder.
 
-### Can I see a sample launch file to learn how to set parameters?
+### Can I see a sample ardrone <node> in a launch file to learn how to set parameters?
 
 
 ```xml
@@ -279,7 +278,7 @@ After successful calibration, press the `commit` button in the UI. The driver wi
     <param name="bitrate" value="2000" />
     <param name="do_imu_caliberation" value="true" />
     <param name="tf_prefix" value="mydrone" />
-    <!-- Covariance Values -->
+    <!-- Covariance Values (3x3 matrices reshaped to 1x9)-->
     <rosparam param="cov/imu_la">[0.1, 0.0, 0.0, 0.0, 0.1, 0.0, 0.0, 0.0, 0.1]</rosparam>
     <rosparam param="cov/imu_av">[1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 1.0]</rosparam>
     <rosparam param="cov/imu_or">[1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 100000.0]</rosparam>
@@ -288,6 +287,7 @@ After successful calibration, press the `commit` button in the UI. The driver wi
 
 ## TODO
 
+* Make the `tf` publish optional.
 * Add separate topic for drone's debug stream (`navdata_demo`)
 * Add the currently selected camera name to `Navdata`
 * Make the `togglecam` service accept parameters