ARToolKit | Mailing List Archive |

ARToolkit question on matrices

From: | Blair MacIntyre <blair@c ............> | Received: | Jul 9, 2005 |

To | joele.d@p ........ | ||

Subject: | Re: ARToolkit question on matrices | ||

M1 =3D M2 * M3 only if M1 and M2 are perfectly correct. There are =20 always errors, unless you have perfect camera calibration and perfect =20= subpixel corner finding for the four corners of the markers; neither =20= of these will be the case with any vision system! So, small errors =20 in both these will result in small (or even large) errors in the pose =20= computation of the camera relative to the marker. Thus, M1 and M2 =20 will have error, and those error will be magnified significantly when =20= you invert one of the matrices (since a small amount of rotation =20 error on the marker will result in huge translation errors in the =20 inverse). A better approach would be to figure out the fixed relationship of =20 the 2 cameras on the rig, get the four corners of the markers in the =20 two images, and use a pose computation that takes all 8 corners =20 across both cameras into account! The stereo info should give you a =20 huge improvement (shouldn't it, folks?). I thought that people had done this already with the AR Toolkit ... But, if your goal is to use the ARToolkit to find the relationship =20 between the cameras, it's not accurate enough. I would suggest =20 looking on the web, there have to be tools for doing this; I know =20 folks do this sort of thing all the time (multicamera calibration). On Jul 9, 2005, at 8:52 AM, joele.d@p ........ wrote: > Hello everybody, > > We have 2 camers mounted on a rig. We can get the transformation > matrix for the first camera and for the second. > > Now we are trying to discover a relation between the 2 matrices. Does > anybody know that relation? > > I have been thinking. Basicly you have one image of the marker in the > first camera, > and a second image of the (same) marker in the second camera. Could I > use, in same way, the RelationTest example? I thought I could use the > relation that the inverse of the first matrix multiplied by the second > matrix gives the relation between marker2 and marker1,let=B4s say M3. > > Would that mean the following: M1 =3D M2*M3? > > Then we are going to move the rig, and the marker stays fixed. Then, > does that relation still hold? I think yes, because with respect to > each other the cameras do not change. > > Any comments are welcome, please. > |

From: | joele.d@p ........ | Received: | Jul 9, 2005 |

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

Subject: | ARToolkit question on matrices | ||

Hello everybody=2C We have 2 camers mounted on a rig=2E We can get the transformation = matrix for the first camera and for the second=2E Now we are trying to discover a relation between the 2 matrices=2E Does = anybody know that relation=3F I have been thinking=2E Basicly you have one image of the marker in the = first camera=2C and a second image of the (same) marker in the second camera=2E Could I = use=2C in same way=2C the RelationTest example=3F I thought I could use t= he = relation that the inverse of the first matrix multiplied by the second = matrix gives the relation between marker2 and marker1=2Clet=B4s say M3=2E= Would that mean the following=3A M1 =3D M2*M3=3F Then we are going to move the rig=2C and the marker stays fixed=2E Then=2C= = does that relation still hold=3F I think yes=2C because with respect to = each other the cameras do not change=2E Any comments are welcome=2C please=2E |