Tracking marker position

[krishna raj]

Hi,

I have applied load on 4 points on head,
on movement ,point force position tracking ,i am going to give the marker position as the point force position
So that point force position moves along the marker position during movement.

How can i get the marker position x,y,z for my 4 Markers, in ground coordinates from the available motion file

It is a 5 sec .mot file.

regards
Krishnaraj GR

[Nicos Haralabidis]

Hello Krishna,

Just to be clear, do you have the coordinates over time for your model? As you could then use the Analyze tool to run a BodyKinematics/Kinematics analysis to get each marker's position in the ground.

Best wishes,

Nicos Haralabidis

[krishna raj]

Hi Nicos,

thank you for the reply.

"coordinates over time for your model" -do you mean the motion file?

The body kinmatics not showing the marker trajectory .

my case:

I have the .mot file ,magnitude of point force (vx,vy,vz) alone ,not having the point position (px,py,pz)
in that case i tried the marker (x,y,z) position as (px,py,pz)

marker1 name:LCAG

i need point trajectory data- LCAGx,LCAGy,LCAGz(ground frame) for the complete motion.

in the attached picture -head is moving forward ,the pressure point is not following the markers.

i have tired the point kinematics also locating my markers ,but result marker point is not exactly matching the location.

if any other way please suggest

regards
krishnaraj gr

[Nicos Haralabidis]

Hello Krishna,

It looks like you have the coordinates/motion file based on your attachment in the previous post - great!

Have your model loaded in the OpenSim GUI, then go Tools -> Analyze... in the input space select Motion and From File, select your motion file. At the top then go to Analyses, at the bottom select Add -> PointKinematics. Select the PointKinematics, at the bottom hit Edit. In the value field of point_name provide a name for your desired point, expand the point field and set the values of the position vector in the local frame. In the field of body_name specify the body name for which the point is expressed locally. In the field of relative_to_body_name specify the ground body. (these instructions may not yield what you expect to see, in which case try body_name as ground and relative_to_body_name the body name for which the point is expressed) If you want more points then add further PointKinematics analyses.

Hope that helps.

Nicos

[krishna raj]

Hi Nicos,

Thanks a lot; it worked for me.
been struggling on this,got it at last

Can you clarify this

My experiment is applying load to four points of the head.

I have the force magnitudes vx vy and vz and now I have the marker position px py px.

So on the external force mot file, I filled in the vx vy and vz -magnitude values, and for the positions px py and pz I filled in the marker position.

The static optimization-muscle force result of with load and without load diff is very small. Any comments on this?

My Doubts:

1. Is it the right way to apply a load to the head through a marker point attached to the skull
2. Is torque necessary or not for the application of point force?
3: After applying the load, the green external forces are not visible; they are seen inside the skull. Does this affect the analysis result?
4. My model is a half-body model. Do I need ground-reaction external forces for my model?

regards
krshnaraj gr