Changes

==Model-based approach for markerless tracking==

==Model-based approach for markerless tracking==

One of the first model-based systems was presented by Comport and colleagues, in the year +2003, and sparked the interest of other researchers. With a model-based tracking, models of the objects or environments to be tracked are used as references for the tracking system. The models from this kind of systems are rendered from different point of views, and there are two basic approaches that use the model images for tracking.<ref name=”1”></ref>

One of the first model-based systems was presented by Comport and colleagues, in the year G2003, and sparked the interest of other researchers. With a model-based tracking, models of the objects or environments to be tracked are used as references for the tracking system. The models from this kind of systems are rendered from different point of views, and there are two basic approaches that use the model images for tracking.<ref name=”1”></ref>

Ziegler (2010) explains that one of the approaches “Extracts features from the model images and video-frames. It then com- pares the features found in a model image with the ones found in a frame. The comparison yields pairs of features which most likely show the same point in the world. These pairs are referred to as correspondences. The tracking system uses the correspondences to estimate the camera’s position and orientation (pose).” A measure of similarity, such as the amount of correspondences, is used to evaluate if the results need refinement by rendering the scene from other point of views. The system will continue refining the results until these meet the threshold defined by the similarity measure.<ref name=”1”></ref>

Ziegler (2010) explains that one of the approaches “Extracts features from the model images and video-frames. It then com- pares the features found in a model image with the ones found in a frame. The comparison yields pairs of features which most likely show the same point in the world. These pairs are referred to as correspondences. The tracking system uses the correspondences to estimate the camera’s position and orientation (pose).” A measure of similarity, such as the amount of correspondences, is used to evaluate if the results need refinement by rendering the scene from other point of views. The system will continue refining the results until these meet the threshold defined by the similarity measure.<ref name=”1”></ref>

==Image processing for markerless tracking==

==Image processing for markerless tracking==

Image processing applied to markerless tracking uses natural features in the images received to calculate the camera’s pose. One of the first applications that used natural features for tracking purposes was presented by Park et al., in the year +1998.<ref name=”1”></ref>

Image processing applied to markerless tracking uses natural features in the images received to calculate the camera’s pose. One of the first applications that used natural features for tracking purposes was presented by Park et al., in the year G1998.<ref name=”1”></ref>

Ziegler (2010) describes this approach as first extracting features from the frames of a video stream and then finding correspondences between succeeding frames. The camera’s pose calculation is made based on these correspondences. Features that where not detected in previous frames are stored and the system calculates their 3D coordinates in order to use them for future correspondence searches. If the system cannot establish a connection to previous frames, tracking fails.<ref name=”1”></ref>

Ziegler (2010) describes this approach as first extracting features from the frames of a video stream and then finding correspondences between succeeding frames. The camera’s pose calculation is made based on these correspondences. Features that where not detected in previous frames are stored and the system calculates their 3D coordinates in order to use them for future correspondence searches. If the system cannot establish a connection to previous frames, tracking fails.<ref name=”1”></ref>