markers coordinate

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Saba
Posts: 1
Joined: Fri Mar 07, 2008 12:03 pm

markers coordinate

Post by Saba » Fri Mar 07, 2008 12:41 pm

hey;
I got some coordinate data from rigid body toolkit ,but I can not find out which marker refers to which coordinate.as I understood coordinates in different frames does n't appear at the same sequence.is there any way to find out the relation in different frames?

Thanks

VincentG
Posts: 7728
Joined: Mon Jul 17, 2006 5:00 am
Location: Corvallis, Oregon

Re: markers coordinate

Post by VincentG » Fri Mar 07, 2008 3:05 pm

Do you have a rigid body defined within the software?

kinemagician
Posts: 2
Joined: Mon Mar 24, 2008 4:09 am
Location: Italy

Re: markers coordinate

Post by kinemagician » Tue Mar 25, 2008 1:10 am

I have a similar problem. This is some info I gathered observing the csv file generated by the RigidBody toolkit:

In the line starting with "rigidbody" there are the coordinates of the markers in the LOCAL REFERENCE FRAME, i.e. the Cartesian system attached to the "Rigid Body 1"

rigidbody,"Rigid Body 1",1,3,0.00999052,-0.00056041,0.08104892,0.02518693,0.00026016,-0.05350043,-0.03517745,0.00030025,-0.02754848

In the line starting with "frame" the marker coordinates are expressed in the ABSOLUTE REFERENCE FRAME
frame,1,1,1,x,y,z,qx,qy,qz,qw,number_of_markers,0.07567394,0.00457156,0.29329556,0.03067580,0.00538698,0.18471199,0.09101386,0.00538093,0.15879589

Unfortunately the marker coordinates in the local frame and in the in the absolute frame are not in the same order.

Therefore if

xA yA zA xB yB zB xC yC zC

is the order of markers A, B, C in local frame, the coordinates of the same markers when expressed in the absolute reference frame is

XB YB ZB XC YC ZC XA YA ZA

I believe that this should be fixed in a next release.

beckdo
NaturalPoint Employee
NaturalPoint Employee
Posts: 519
Joined: Tue Jan 02, 2007 2:02 pm

Re: markers coordinate

Post by beckdo » Tue Mar 25, 2008 6:26 pm

The tracking toolkits do not label the point cloud markers. As a result, the markers essentially are listed in an arbitrary order. The markers that are listed for each rigid body are the markers that were defined for that rigid body fit into the point cloud. Since there is a small amount of error in the entire system, you'll find that the markers listed for a given rigid body will match up to markers listed in the point cloud, but their locations will off by a small amount. This small amount represents the error in the system at that location within the capture volume.

Hope this helps.

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