To the user of this system, it would appear that he is looking at a single scene. Show image a few slides back: Shows the merging and correct registration of pre-operative data and the patient’s head. Providing this view to a surgeon in the operating room would: Enhance the surgeon’s performance Possibly eliminate the need for any other calibration fixtures during the operation
Computer generated virtual objects must be accurately registers with the real in all dimensions. Errors in registration prevent the real and virtual images from being seen as fused. Registration must be maintained while the user moves around in the virtual environment. Changes in registration can be distracting or physically disturbing.
Augmented reality is closest to the real world because mainly a user is perceiving the real world with just a little computer generated data. This distinction will probably fade as technology improves.
Reproduction Fidelity Quality ranges from wireframe approximations to completely photorealistic renderings. Real-time constraints forces AR to be on the low end of this axis. Extent of Presence Metaphor AR is on low end of this axis too. Closely related to display technology - each gives a different sense of immersion Extend of World Knowledge In some domains this information is well known - which makes AR easier.
Need these things to seamlessly combine the real and virtual worlds. Need precise models of the user’s environment and how it is sensed.
1st picture - real world 2nd picture - real world with virtual objects and inter-reflections and virtual shading
Imaging device is a video camera in this case Camera performs perspective projections of 3D world onto 2D image plane using the focal length, lens distortion, position, and pose of the device to determine exactly what is projected onto the image plane. Virtual objects modeled in an object reference frame and generated by a standard computer graphics system. Graphics system requires information about the imaging of the real scene so that it can correctly render these objects. Virtual image merged with real scene image to form augmented reality image.
Want to render virtual parts without any visible jumps (real-time constraints.) Standard rule of thumb - graphics system must be able to render the virtual scene at least 10 times/sec - this is well within current capabilities for moderately complex graphics scenes. There are a lot of Augmented Reality applications that have virtual parts that are not very complex and do not require high levels of photorealism.
AR systems sensitive to visual errors - virtual object may not be stationary in the real scene or it may be in the wrong place. Misregistration of a pixel can be detected under certain conditions. Time delays lead to augmented image lagging behind motions in the real scene.
Sometimes referred to as “Windows on the World” or “Fish Tank VR” Other display technologies are used to increase the sense of presence.
Works by placing optical combiners in front of the user’s eyes. Combiners are partially transmissive - so user can look directly through them and see the real world. Combiners are partially reflective - so user can also see virtual images bounced off the combiners from head-mounted monitors. Similar to Head-Up Displays (HUDs) commonly used in military aircraft. Can see through the display even if the power is turned off.
Works by combining a closed-view HMD with one or two head-mounted video cameras Video cameras provide the user’s view of the real world. Video from cameras is combined with graphics images by the scene generator to blend the two worlds. Result is sent to the monitors in from on the user’s eyes in the closed-view HMD. User has no direct view of the real world. If power is off, the user is “blind.”
Color selected cannot be used in the virtual object. Depth Information allows for occlusion.
Flexibility in composition strategies Basic Problem with optical is the virtual objects do not completely obscure real- world objects because combiners allow light from both the virtual and real sources. Virtual objects appear ghost-like and semi-transparent, damaging the illusion of reality because occlusion is a strong depth cue. Video see-through is much more flexible about how it merges real and virtual - they are both in digitized form so compositors can do a pixel-by-pixel comparison. Produces more compelling environments. Wide Field of View Distortions in optical systems are a function of the radial distance away from the optical axis - the further you look away from the center of the view, the more distorted it gets. A digitized image taken through a distorted optical system can be undistorted by applying image processing techniques to unwarp the image. This requires significant amounts of computation - but this constraint will lessen as computers become faster. It is harder to build wide FOV displays with optical see-through constraints. Distortions of the user’s view of the real world could be corrected optically, but complex optics are expensive and make the HMD heavier. Real and Virtual delays can be matched Delay the video of the real world to match the delay in the virtual image stream. (can’t be done in optical because it gives the user a direct view of the real world.) Disadvantage: eliminating dynamic error comes at the cost of delaying both the real and virtual scenes - user sees everything lagging behind.
Simplicity Optical has only 1 stream of video to worry about (the graphics images), while Video has separate streams for real and virtual images. Optical - real world is seen directly through combiners with a time delay of a few nanoseconds while both delays in video are in 10s of milliseconds. Optical HMDs with narrow field of view combiners offer views of the real world that are basically undistorted, while Video has distortion that must be compensated for. Resolution Video limits the resolution of what the user sees (both real and virtual) to the resolution of the display devices. Optical limits the virtual resolution to the resolution of the display devices but not the user’s view of the real world. No Eye Offset Video - user’s view of real world is provided by video cameras that are not necessarily located at exact positions of user’s eye - creating an offset between cameras and real eyes. Video problem can be avoided using mirrors to create a set of optical paths that mimic the direct path to the user’s eyes, however this adds complexity to the HMD design. Offset is not generally a problem for optical.
ugmented Reality BY Dr.Hatem Mohammed
Augmented Reality Goals Taxonomy Technology
What is Augmented Reality? <ul><li>A combination of a real scene viewed by a user and a virtual scene generated by a computer that augments the scene with additional information. </li></ul>
What is the Goal of AR? <ul><li>To enhance a person’s performance and perception of the world </li></ul><ul><li>But, what is the ultimate goal???? </li></ul>
The Ultimate Goal of AR <ul><li>Create a system such that no user CANNOT tell the difference between the real world and the virtual augmentation of it. </li></ul>
Augmented Reality vs. Virtual Reality <ul><li>Augmented Reality </li></ul><ul><li>System augments the real world scene </li></ul><ul><li>User maintains a sense of presence in real world </li></ul><ul><li>Needs a mechanism to combine virtual and real worlds </li></ul><ul><li>Virtual Reality: </li></ul><ul><li>Totally immersive environment </li></ul><ul><li>Visual senses are under control of system (sometimes aural and proprioceptive senses too) </li></ul>
Miligram’s Reality-Virtuality Continuum Mixed Reality (MR) Real Environment Virtual Environment Augmented Reality (AR ) Augmented Virtuality (AV) Miligram coined the term “Augmented Virtuality” to identify systems which are mostly synthetic with some real world imagery added such as texture mapping video onto virtual objects.
Miligram’s Taxonomy for Mixed Reality Displays <ul><li>Reproduction Fidelity – quality of computer generated imagery </li></ul><ul><li>Extent of Presence Metaphor – level of immersion of the user within the displayed scene </li></ul><ul><li>Extent of World Knowledge – knowledge of relationship between frames of reference for the real world, the camera viewing it, and the user </li></ul>Reproduction Fidelity Extent of Presence Metaphor Extent of World Knowledge
Combining the Real and Virtual Worlds <ul><li>We need: </li></ul><ul><li>Precise models </li></ul><ul><li>Locations and optical properties of the viewer (or camera) and the display </li></ul><ul><li>Calibration of all devices </li></ul><ul><li>To combine all local coordinate systems centered on the devices and the objects in the scene in a global coordinate system </li></ul>
Combining the Real and Virtual Worlds (cont) <ul><li>Register models of all 3D objects of interest with their counterparts in the scene </li></ul><ul><li>Track the objects over time when the user moves and interacts with the scene </li></ul>
Realistic Merging <ul><li>Requires: </li></ul><ul><li>Objects to behave in physically plausible manners when manipulated </li></ul><ul><li>Occlusion </li></ul><ul><li>Collision detection </li></ul><ul><li>Shadows </li></ul><ul><li>**All of this requires a very detailed description of the physical scene </li></ul>
Research Activities <ul><li>Develop methods to register the two distinct sets of images and keep them registered in real-time </li></ul><ul><ul><li>New work in this area has started to use computer vision techniques </li></ul></ul><ul><li>Develop new display technologies for merging the two images </li></ul>
Performance Issues <ul><li>Augmented Reality systems are expected: </li></ul><ul><li>To run in real-time so that the user can move around freely in the environment </li></ul><ul><li>Show a properly rendered augmented image </li></ul><ul><li>Therefore, two performance criteria are placed on the system: </li></ul><ul><li>Update rate for generating the augmenting image </li></ul><ul><li>Accuracy of the registration of the real and virtual image </li></ul>
Limitations for Updating the Generated Images <ul><li>Must be at 10 times/second </li></ul><ul><li>More photorealistic graphics rendering </li></ul><ul><li>Current technology does not support fully lit, shaded and ray-traced images of complex scenes </li></ul>
Failures in Registration <ul><li>Failures in registration due to: </li></ul><ul><ul><li>Noise </li></ul></ul><ul><ul><ul><li>Position and pose of camera with respect to the real scene </li></ul></ul></ul><ul><ul><ul><li>Fluctuations of values while the system is running </li></ul></ul></ul><ul><ul><li>Time delays </li></ul></ul><ul><ul><ul><li>In calculating the camera position </li></ul></ul></ul><ul><ul><ul><li>In calculating the correct alignment of the graphics camera </li></ul></ul></ul>
Video Composition for Video see-through HMD <ul><li>Chroma-keying </li></ul><ul><ul><li>Used for special effects </li></ul></ul><ul><ul><li>Background of computer graphics images is set to a specific color </li></ul></ul><ul><ul><li>Combining step replaces all colored areas with corresponding parts from video </li></ul></ul><ul><li>Depth Information </li></ul><ul><ul><li>Combine real and virtual images by a pixel-by-pixel depth comparison </li></ul></ul>
Advantages of Video see-through HMD <ul><li>Flexibility in composition strategies </li></ul><ul><li>Wide field of view </li></ul><ul><li>Real and virtual view delays can be matched </li></ul>