Camera Calibration

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As you can see, the quality of the tracking system and the correctness of the final result are influenced by the configuration of the whole system. The camera calibration plays an important role, because it is used by the two fundamental components of an AR application: the tracking system and the rendering system.

Please also take a look at the camera calibration in the Unifeye Design documentation which also describes some basics about camera calibration.

The Unifeye SDK offers an interface for two kinds of camera calibrations, giving the user the flexibility to choose between

1. Standard camera calibration. It is based on the camera model proposed by Zhang in 1998 and estimates the intrinsic camera parameters such as focal length, principal point and distortion based on different views of a known planar pattern.
   Within the Unifeye SDK this calibration is available through the Sextant Tool (reference from Unifeye Design documentation). Calibration patterns can be printed and then used directly to do a calibration. The approach is very easy and fast and perfectly sufficient for cameras without high-precision optics such as general web cameras.
2. Extended camera calibration. In contrast to standard calibration, the extended version is intended for usage with high-quality digital cameras with stable and precise optics. The calibration model is for instance described by Luhmann et al. in the book "Close range photogrammetry". It approximates the intrinsic camera parameters in more detail than the standard calibration model above using a 3D high-precision calibration board.
   In order to provide extended camera calibration, metaio uses external Software (e.g. AICON) for the calibration process. Furthermore metaio provides the Extended Sextant Tool for conversion from AICON native ".ior" format to a binary format, which can be used within Unifeye SDK. The binary format (.bin) takes several calibration results (provided in ".ior" format) and merges them statistically to one calibration. This is the recommended way for high precision approaches. Nevertheless the Unifeye SDK can also load ".ior" files directly.

The choice of calibration should depend on the actual need for accuracy in the given application and the stability and quality of the used camera.

Load Camera Calibration files

Once the camera calibration is done or extended sextant file is generated it can be easily loaded into Unifeye using two camera calibration tools provided in the "Configuration" panel of the Unifeye GUI.

• Loading a standard camera calibration files can be done using "Camera Calibration"-Panel (see (1) in Figure above).
• The extendend sextant calibration files can be loaded using the "Extendend Sextant Calibration"-Panel (see (2) in Figure above).

In order to start camera calibration process (using Sextant Tool) or generation of extended camera calibration file (using Extended Sextant Tool) you can click the "Open Sextant" respectively "Open Extended Sextant" buttons in appropriate panels.

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-- SupportMetaio - 2011-01-21