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The user will remember the fact that what they seen is unreal if any delay occurs during the
interaction [7]. Especially during without pre-processing time allowed, the requirement for a real-time
system is far more difficult to be done.

Challenges and Problem Areas Analysis: Technical Requirement
Implementation of Mixed Reality (MR) is demanding numbers of technological requirements. The
most significant challenge is on its display technology where high resolution and contrast needed in
visualize digital objects. The next challenge is on the position track. The system needs to determine
the position of the relevant objects relative to the display system in order to give the illusion that the
virtual objects located on a fixed physical location or attached to physical items. Below is the section
of overview on the display and tracking technologies used in the implementation of mixed reality
systems and their limitation [9].

Displays: Head-Mounted Displays (HMD)
The most common type of displays used in mixed reality, although it is originally designed for using
with Virtual Reality (VR) systems. The display is very close to the user’s eyes, which including one
or two display units altogether with optically compensated systems to from a perceptively correct
virtual image. HMD for VR only developed to let users see what is shown on the display only, but not
able to see through. The virtual imagery for mixed reality needs to mixed with the surrounding
environment imagery. However, this could be done by attaching a video camera on the HMD, which
the synthetic images are electronically combined with the images captured by the camera. For more
optical combination of physical and virtual imagery, another solution is by using a semi-transparent
mirror on the HMD.

Displays: Handheld Displays
By using the metaphor of magic lens, handheld display is used for mixed reality, through which some
virtual elements are added into reality. Same as HMD, the virtual image will only generate when the
position and orientation of the handheld display is known. It is cheaper compared to the HMD and no
need for any optical compensation. The most common use of this display currently is on smartphones
and tablets.

Displays: Ambient Projectors
This method is different from others displays where the computer generated images is projected
directly into the environment. The projection can in an entire room or onto a specific object, but
requires a 3D model of the entire space. In this way, the images to projection surfaces which are not
perpendicular to projector could be fit with the distortion of the projection. The projector are not
movable unlike HMD and handheld display, thus it reduce the needs of tracking but limits the
movement of users.

Registration System: Global Positioning System (GPS)
Global GPS receivers use radio signals broadcasted by earth orbit satellites for calculation of location
[10]. The position of other satellites in the system will be continuously transmitted by sending
message between each satellite. GPS is broadly used in navigation and guidance in civilian vehicle
such as cars, planes and ships, and also for outdoor mixed reality systems. The resolution of the
positioning will be influenced by the sensitivity and accuracy of the receivers since the system is
based on the radio signal timing [11]. GPS signals can be obstructed when in indoor or block by high
buildings due to the receiver fail to connect with satellites. The radio reception can also vary
depending on the weather of a location. All this will cause more problems with GPS signals.

Registration System: Visual Markers
Visual markers are known as fiducial markers are graphical symbols designed in combination with a
computer vision recognition algorithm to yield a high probability of recognition and low probability
of misclassification [12]. In mixed reality systems, visual markers are used with camera together with
the display such as attach with projectors, handheld display and HMD for the virtual element to be
rendered correctly in position. These hidden markers containing virtual elements can be rendered