ARToolKit | Mailing List Archive |

rotation around X

From: | Brendan <brendan@c ............> | Received: | Mar 19, 2002 |

To | artoolkit@h .................. | ||

Subject: | rotation around X | ||

I'm using the ARToolkit as an object tracker in an application, and it seems like all the transformations that arGetTransMat returns have been rotated around the X-axis by 180 degrees. Should the matrix that this function calculates be the transformation of the object in the camera's coordinate system ? If so, a feducial help upright directly in front of a camera should return the identity matrix with just a translation in the -Z direction. My app is returning this matrix, but then multiplied by a 180 degrees around the X-axis rotation matrix. But the graphics get drawn correctly when I load the returned matrix into my (modelview) matrix stack. what am I misunderstanding? shouldn't positive z values imply that the feducial is behind the camera ? thanks all, brendan hannigan Brendan Hannigan | brendan@c ............ | http://www.hannigan.org -------------------------------------------------------------------------- |

From: | Hirokazu Kato <kato@s ........................> | Received: | Mar 22, 2002 |

To | artoolkit@h .................. | ||

Subject: | Re: rotation around X | ||

Hi, >If so, a feducial help upright directly in front of a camera should >return the identity matrix with just a translation in the -Z direction. No. I put a figure which shows coordinates systems in ARToolKit at: http://www.sys.im.hiroshima-cu.ac.jp/people/kato/etc/ATK-coordinates.jpg As we can see in the figure, when the marker is put in front of the camera, the direction of Y-axis and Z-axis are opposite between camera coordinates and marker coodinates. This means that transformation matrix between marker and camera includes 180 degree rotation in X-axis. Also translation in Z-axis should be plus. -- ------------------------------------------------------------------ Hirokazu Kato Faculty of Information Sciences Hiroshima City University Phone: 082-830-1705 Email: kato@s ........................ Fax: 082-830-1435 URL: http://www.sys.im.hiroshima-cu.ac.jp/people/kato/ |