Control Raspberry Pi via VNC and setup virtual server on router/AP

The setup concept is like following diagram

VNC client<-->Internet<-->router<-->Raspberry Pi

1. Setup VNC server
• sudo apt-get install tightvncserver
• vncserver -geometry 1024x768 -depth 24 and set password, this password is only used for VNC login
• You will require a password to access your desktops.
  
  
  Password: 
  Warning: password truncated to the length of 8.
  Verify:   
  Would you like to enter a view-only password (y/n)? n
  
  
  New 'X' desktop is raspberrypi:1
  
  
  Creating default startup script /home/pi/.vnc/xstartup
  Starting applications specified in /home/pi/.vnc/xstartup
  Log file is /home/pi/.vnc/raspberrypi:1.log
• :1 is desktop number which stands for VNC port is 5901
2. Setup virtual server on router/AP
• Enter virtual server settings in router
• Name: RPi
• IP address: loca network address of RPi, 192.168.x.y for example
• Public port: choose a valid port number, 8899 for example
• Private port: 5901
• Protocol: choose both TCP and UDP
3. Connect to Raspberry Pi

• Check your worldwide IP address on Internet, w.x.y.z
• Open VNC client and enter address like w.x.y.z:8899
• Connect and it should work

Reference: http://www.maketecheasier.com/setting-vnc-raspberry-pi/