install usb_cam with:
 sudo apt-get install ros-indigo-usb-cam

copy the launch file:
/opt/ros/indigo/share/usb_cam/launch/usb_cam-test.launch
to an editable location and change video_device to /dev/video1 to use the external camera

run
roslaunch ~/usb_cam-test.launch
to start it

add:
export ROS_PACKAGE_PATH=${ROS_PACKAGE_PATH}:/home/abhineet/ORB_SLAM2/Examples/ROS
export LIBRARY_PATH=${LIBRARY_PATH}:/home/abhineet/ORB_SLAM2/lib:/home/abhineet/ORB_SLAM2/Thirdparty/DBoW2/lib:/home/abhineet/ORB_SLAM2/Thirdparty/g2o/lib
export LD_LIBRARY_PATH=${LD_LIBRARY_PATH}:/home/abhineet/ORB_SLAM2/lib:/home/abhineet/ORB_SLAM2/Thirdparty/DBoW2/lib:/home/abhineet/ORB_SLAM2/Thirdparty/g2o/lib
to bashrc

run orb slam with:
rosrun ORB_SLAM2 Mono Vocabulary/ORBvoc.txt Examples/Monocular/mono.yaml /camera/image_raw:=usb_cam/image_raw
using params:

# Camera calibration and distortion parameters (OpenCV) 
Camera.fx: 674.828820
Camera.fy: 671.076483
Camera.cx: 313.837639
Camera.cy: 249.457471

Camera.k1: -0.074566
Camera.k2: 0.099668
Camera.p1: -0.000740
Camera.p2: -0.002609
Camera.k3: 0.000000

# Camera frames per second 
Camera.fps: 30.0

# Color order of the images (0: BGR, 1: RGB. It is ignored if images are grayscale)
Camera.RGB: 1

gmapping launch location:
/opt/ros/indigo/share/turtlebot_navigation/launch/gmapping_demo.launch

run orb slam on KITTI with:
./Examples/Monocular/mono_kitti Vocabulary/ORBvoc.txt Examples/Monocular/KITTI00-02.yaml /home/abhineet/KITTI/00
./Examples/Monocular/mono_kitti Vocabulary/ORBvoc.txt Examples/Monocular/KITTI04-12.yaml /home/abhineet/KITTI/05
run on TUM-RGBD with:
./Examples/Monocular/mono_tum Vocabulary/ORBvoc.txt Examples/Monocular/TUM3.yaml /home/abhineet/TUM-RGBD/rgbd_dataset_freiburg3_walking_halfsphere

navigate using the map and visualize with:
roslaunch turtlebot_gazebo turtlebot_world.launch
or
roslaunch turtlebot_gazebo turtlebot_world.launch world_file:=/opt/ros/indigo/share/turtlebot_gazebo/worlds/empty.world
for empty world
roslaunch turtlebot_gazebo amcl_demo.launch map_file:=/home/abhineet/ORB_SLAM2/grid_map.yaml
roslaunch turtlebot_rviz_launchers view_navigation.launch

running orb slam with gmapping:
rosrun ORB_SLAM2 Mono Vocabulary/ORBvoc.txt Examples/Monocular/KITTI00-02.yaml  /home/abhineet/KITTI/00
rosrun pointcloud_to_laserscan pointcloud_to_laserscan_node
rosrun gmapping slam_gmapping
rosrun rviz rviz
Displays->Add->Map
set Topic to /map

get all map points for the rosbag:
rosrun ORB_SLAM2 Mono Vocabulary/ORBvoc.txt Examples/Monocular/demo_cam.yaml /camera/image_raw:=usb_cam/image_raw

start publisher with dataset:
rosrun ORB_SLAM2 Monopub Vocabulary/ORBvoc.txt Examples/Monocular/KITTI00-02.yaml /home/abhineet/KITTI/00 0
rosrun ORB_SLAM2 Monopub Vocabulary/ORBvoc.txt Examples/Monocular/TUM3.yaml /home/abhineet/TUM-RGBD/rgbd_dataset_freiburg3_walking_halfsphere
start publisher with camera:
rosrun ORB_SLAM2 Monopub Vocabulary/ORBvoc.txt Examples/Monocular/mono.yaml 0
start publisher with default topic (/camera/image_raw):
rosrun ORB_SLAM2 Monopub Vocabulary/ORBvoc.txt Examples/Monocular/mono.yaml -1
start publisher with custom topic:
rosrun ORB_SLAM2 Monopub Vocabulary/ORBvoc.txt Examples/Monocular/demo_cam.yaml -1 /usb_cam/image_raw

start subscriber on kitti 00:
rosrun ORB_SLAM2 Monosub 5 3 29 -25 48 -12 0.55 0.50 1 5
rosrun ORB_SLAM2 Monosub 10 1 29 -25 48 -12 0.55 0.50 1 5

start subscriber on rosbag:
rosrun ORB_SLAM2 Monosub 30 5 2 -2 2 -2 0.55 0.50 1 5
rosrun ORB_SLAM2 Monosub 30 2 6 -6 6 -6 0.55 0.50 1 5
rosrun ORB_SLAM2 Monosub 10 0.5 20 -10 20 -10 0.55 0.50 1 5

running rosbag of recording:
rosbag play "/media/abhineet/Win 8/bags/2017-04-03-20-35-36.bag" -r 0.5
rosbag play 2017-04-09-22-08-04.bag -r 0.5
rosbag play "/media/abhineet/Win 8/bags/2017-04-03-13-37-07.bag" -r 0.5

running rviz with preloaded map display and topic name:
rosrun rviz rviz -d grid_map.rviz