[ARToolKit] How does ARToolKit Work?

ARToolKit



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→Beginner:Getting Started:How does ARToolKit Work?


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How does ARToolKit work?

Basic Principles(基本原則)

ARToolKit應用可以讓虛擬圖像是疊加在視訊畫面。
這個秘密在於將黑色方塊作為tracking(追蹤)標記。

該ARToolKit 的 tracking工作原理如下：

1. 該camera拍攝的視頻畫面，將其發送到電腦。
2. 在computer上的軟體，檢查通過每個視訊畫面的所有的方形。
3. 如果找到一個正方形，該軟體使用一些數學運算來計算黑色方塊對應camera 的位置。
4. 一旦camera的位置是已知的，computer graphics model 也會在同樣位置顯示。
5. model在視頻的現實世界顯示，出現在marker上的方塊。
6. 最終輸出顯示在手持式顯示器，因此當user通過顯示器看起來，他們看到的圖形疊加在真實的世界。



下圖總結了這些步驟。
ARToolKit能夠執行此camera的即時tracking，確保虛擬物件總是出現疊加在tracking markers上。



(看不清楚,請點圖.)


(圖內容待補...)


Limitations (限制)


有一些限制，純粹基於computer vision(顯示)的AR系統。
當然，如果是虛擬物件將只出現在tracking marks 的範圍內。
這可能會限制大小和虛擬物件的運動。
這也意味著，如果users他們的手或其他物體覆蓋部分圖像，虛擬物件將消失。


---------------(以下待補)---------------
There are also range issues.
The larger the physical pattern the further away the pattern can be detected and so the great volume the user can be tracked in.
Table 1 shows some typical maximum ranges for square markers of different sizes.
These results were gathered by making maker patterns of a range of different sizes (length on a side),
placing them perpendicular to the camera and moving the camera back until the virtual objects on the squares disappeared.




Table 1: Tracking range for different sized patterns.




This range is also affected somewhat by pattern complexity.
The simpler the pattern the better.
Patterns with large black and white regions (i.e. low frequency patterns) are the most effective.
Replacing the 4.25 inch square pattern used above,
with a pattern of the same size but much more complexity,
reduced the tracking range from 34 to 15 inches.




Tracking is also affected by the marker orientation relative to the camera.
As the markers become more tilted and horizontal,
less and less of the center patterns are visible and so the recognition becomes more unreliable.




Finally, the tracking results are also affected by lighting conditions.
Overhead lights may create reflections and glare spots on a paper marker and so make it more difficult to find the marker square.
To reduce the glare patterns can be made from more non-reflective material.
For example, by gluing black velvet fabric to a white base.
The 'fuzzy' velvet paper available at craft shops also works very well.







You will find more informations on computer vision principle at this page, or more informations on performance at this page.