Development of an Augmented Reality system using ARToolKit

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Development of an Augmented Reality system using ARToolKit and user invisible markers connected to the computer. In Figure 4.23 and 4.24 are shown the camera itself and its system requirements. Requirements • Intel Pentium II or better • Windows 2000 or XP Figure 4.23 Dragonfly Figure 4.24 Requirements Figure 4.25 FireFly2 The second camera, the FireFly2, is delivered by the same company. It has properties similar to the camera described before. It is also delivered with a 6pin IEEE 1394 cable and an IEEE 1394 PCI interface card. Differences are the size of the image sensor, the resolution, the type and the size of the camera. This camera has a 1/4” Sony CCD image sensor with dimensions of 40x40mm. The only resolution and type available is a 640x480 colour image sensor. The maximum frame rate is 30fps. The weight of the camera including a micro lens is 12grams. Figure 4.25 displays the camera. The system requirements are the same as in Figure 4.24. Both the Dragonfly and the FireFly2 cameras are delivered with 3 micro lenses. The focal lengths of these are 4, 6 and 8mm. The lens holders for both cameras are designed to accommodate lenses that are designed according to the M12 standard; that is, the diameter is 12mm and the thread pitch is 0.5mm. The DragonFly camera is delivered with a C/CS mount lens holder. The FireFly2 does not include such a lens holder, but it can be obtained. Now the difference between micro lenses, C mount and CS mount lenses is explained. 4.4.1 Lenses Micro lenses are designed for use in micro CCD board. They can cover a variety of CCD formats, including the 1/3” and 1/4” size CCD. C and CS-mount lenses are both threaded lens mounts found on most industrial CCD cameras. The difference between C and CS-mount equipment is displayed in Figure 4.26. The flange back distance is the distance between the sensor image plane and the flange of the camera (the part of the case that buts up against the camera). For CSmount lenses this is 17.52mm and for C-mount cameras 12.52mm. The focus can be corrected by placing a 5mm spacer. This only works with a CS-mount camera. Then both types of lenses can be used, CS-mount and C-mount lenses. 47
Development of an Augmented Reality system using ARToolKit and user invisible markers Figure 4.26 The difference between C-mount and CS-mount lenses So, with a CS-mount camera there are three possibilities to choose for the lens; a micro lens, a CS-mount lens or a C-mount lens. To have a camera to be IR sensitive first the internal IR blocking filter needs to be removed. Contact with the company that delivers the cameras has shown that the company is willing and able to remove the internal IR blocking filter. After this has been done the camera needs a suitable IR cut off filter to make it able to detect light in the infrared range. The cameras are delivered with 3 types of lenses; 4mm, 6mm and 8mm. Properties of the lenses are displayed in Figure 4.27. Any IR filter that has similar properties should be able to fit the cameras. Figure 4.27 Lens properties of DragonFly and FireFly2 cameras It would be very handy if the IR filters described before would fit the Point Grey Research cameras. Then no other search for suitable filters would have been needed. But this is not the case; the diameter sizes of the cameras and the IR filters do not meet. That means that more information on IR filters needs to be gathered. It seems that there is no standard information that all manufacturers provide. There are two possibilities for the IR filter. One round filter that fits the lens of the camera could be used. This type of filter will be hardest to find because of the diversity of available information. The other possibility is an IR filter that has a size bigger than the diameter of the lens. This filter then could be put in front of the camera’s lens. This will be a square sized filter, because usually those are made from sheet material. 48
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Development of an Augmented Reality system using ARToolKit

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