1. Bumblebee XP3 3D. https://www.ptgrey.com/bumblebee-xb3-1394b-stereo-vision-camera-systems-2
2. Duo 3D Camera. https://duo3d.com/
3. Face Detection. https://developer.android.com/reference/android/media/FaceDetector.html
4. Ultrasonic sensors Find Direction And distance. http://www.maxbotix.com/documents/MaxBotix_Ultrasonic_Sensors_Find_Direction_and_Distance.pdf
5. Visual impairment and blindness. http://www.who.int/mediacentre/factsheets/fs282/en/