Development of an Augmented Reality system using ARToolKit
Development of an Augmented Reality system using ARToolKit
Development of an Augmented Reality system using ARToolKit
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<strong>Development</strong> <strong>of</strong> <strong>an</strong> <strong>Augmented</strong> <strong>Reality</strong> <strong>system</strong> <strong>using</strong> <strong>ARToolKit</strong> <strong>an</strong>d user invisible markers<br />
Figure 3.9 Application steps <strong>an</strong>d their corresponding <strong>ARToolKit</strong> functions<br />
Steps 2 through 5 have been discussed earlier, <strong>an</strong>d are repeated continously, while steps<br />
1 <strong>an</strong>d 6 are only performed on initialization <strong>an</strong>d shutdown <strong>of</strong> the application. The<br />
application may also need to respond to occuring events. A program consists <strong>of</strong> a main<br />
routine that carries out the actions in step 1, by <strong>using</strong> the init function. Within the main<br />
routine the argMainLoop function is responsable for calling the functions that<br />
correspond to the application steps 2 through 5. Closing the application will make the<br />
cle<strong>an</strong>up function stop the video processing <strong>an</strong>d close down the video path.<br />
A video image is captured <strong>an</strong>d displayed on the screen, either a warped image corrected<br />
for camera distortions or <strong>an</strong> unwarped image. arDetectMarker is used to search the<br />
image for markers, which already have been read in by the init function. The function<br />
delivers the number <strong>of</strong> found markers, <strong>an</strong>d information concerning markers in the<br />
marker_info structure. This contains the coordinate information <strong>an</strong>d recognition<br />
confidence values <strong>an</strong>d object id numbers for each <strong>of</strong> the markers. For finding the<br />
tr<strong>an</strong>sformation between the markers <strong>an</strong>d the camera arGetTr<strong>an</strong>sMat function is used.<br />
Finally, virtual objects are drawn by the draw function, based upon the association <strong>of</strong><br />
virtual objects <strong>an</strong>d marker patterns read in by init.<br />
3.5 Training marker patterns<br />
To allow <strong>ARToolKit</strong> to carry out its main functionality <strong>of</strong> overlaying virtual objects on<br />
fiducial markers, it needs to be taught the different marker patterns to recognize. These<br />
are specified in a text file, by stating the name <strong>of</strong> the marker, its corresponding pattern<br />
<strong>an</strong>d its width. Patterns to be recognized c<strong>an</strong> be created by <strong>an</strong> <strong>ARToolKit</strong> subprogram<br />
that makes template files. For doing so one first needs to print out <strong>an</strong> empty pattern file,<br />
just containing a black square with a white square in the middle. Then a pattern needs to<br />
be attached to the white square, either a black <strong>an</strong>d white or color one. The pattern<br />
recognition program is used to capture this pattern, preferably under similar lighting<br />
conditions as when the AR application will be running. When the pattern is found this is<br />
indicated by <strong>an</strong> appearing red <strong>an</strong>d green square around it. The camera should be rotated<br />
until the red corner <strong>of</strong> the highlighted square is in the top left h<strong>an</strong>d corner. Figure 3.10<br />
shows <strong>an</strong> identified marker pattern. Then the pattern is stored in a bitmap file <strong>an</strong>d c<strong>an</strong> be<br />
used in AR applications.<br />
Figure 3.10 Training marker patterns<br />
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