Topic: Custom (human) drawing tools

hello there,
I'm using v. 0.8.27 (experimental). I have two concrete support questions (1-2) and two whishlist entries (3-4):

1) what inertial parameters (i.e., segment mass) do you use to estimate total body center of mass location for the "human model"? Dampster? De Leva? Etc..

2) I might have missed something but...why I cannot modify the size (i.e., segments length) of the "profile" model? I had a look into the xml file and it looks constrained.

3) could it be possibile in the future having a center of mass for the "profile" model too (I'm thinking at computing lumbar compression force and moment during deadlift/squat through inverse dynamics and it requires center of mass location as well as trunk angles)

4) would it be even possible in the future to have a tool or add-on (a kind of GUI to friendly create a xml file) to build our own model by specifying body segments to use along with the relevant inertial parameters, joint angles and so on?


Many thanks for your support,
Pietro

Re: Custom (human) drawing tools

Hi,

First I want to say that I'm very motivated to improve this part of the application smile

1) what inertial parameters (i.e., segment mass) do you use to estimate total body center of mass location for the "human model"? Dampster? De Leva? Etc..

I thought I had put a comment inside the XML to document the source but apparently I must have forgotten… Unfortunately at the moment I can't find the exact reference I used for the coefficients. It might have been from a book annex.

Please point to popular models that are used in your field and we'll build the corresponding tools. I want the user to be able to pick between several models anyway.

2) I might have missed something but...why I cannot modify the size (i.e., segments length) of the "profile" model?

Yeah the profile model is a bit restrictive. I actually considered replacing it for last release. It was created based on a specific scenario where it was not used to draw over a person segments but to act as a quick reference diagram on the side. The person would move the segments a bit to make a canonical pose as a note. I don't think this scenario is in use anymore.

3) could it be possibile in the future having a center of mass for the "profile" model too

Yes if we have the coefficients based on the existing segments. Post them and we'll build the tool.

I'm thinking at computing lumbar compression force and moment during deadlift/squat through inverse dynamics and it requires center of mass location as well as trunk angles

I started to update the format for last release, and plan to update it again to make it easier to display computed measures.

My goal would be to be able to display ratios, additions of two segments length, etc. There is a ton of these standard metrics that can be done based on anatomical landmarks and are referenced throughout the literature.

I'm still at the design phase for the framework to make these computations possible. My thinking so far is to add a concept of variables and operators and the tool would declaratively describe a resulting variable by using an algebraic expression tree. This would replace the "computed point" concept and be way more powerful.

There are also several primitives that are missing at the moment, like the possibility to get the angle between two non-intersecting segments, and get the center of a best-fit circle from a few points.

Please send how you perform the measure manually and any bibliographical references we can use. This will greatly help this design phase.

4) would it be even possible in the future to have a tool or add-on (a kind of GUI to friendly create a xml file) to build our own model by specifying body segments to use along with the relevant inertial parameters, joint angles and so on?

It has been a dream of mine but it would be a very big undertaking. For the initial skeleton structure it might be possible to use another application or a Kinovea key frame and convert/import the set of segments into a tool, but that won't help with variables and behavior. So it is going to be a manual process for the time being.

Re: Custom (human) drawing tools

I reviewed the de Leva model and can say that it is not the one used in the tool. It's also not the Zatsiorsky-Seluyanov model.

One issue that always bugged me, I'm not too convinced that the full body models make a lot of sense when used on 2D images, as the segments and landmarks can't possibly be on the same plane, so the lengths and COM coordinates of some of the segments are going to be inaccurate relatively to the rest. Are you aware of existing research on how these full body model can be adapted to 2D or the magnitude of error to expect?

Re: Custom (human) drawing tools

Widely used (in biomechanics) are Dempster's segment endpoint definitions & Dempster's body segment parameters (yes, also center of mass).
Both are summarized here: http://health.uottawa.ca/biomech/course … mpster.pdf
Will check the literature on joan's last post.
Following the gut feeling, isolated movements taking place in one plane & recorded with aligned/calibrated setup might be arguably approximated for such analyses.
If you are aiming at research grade inverse dynamics results, 3D kinematics/kinetics measures remain the gold standard...
For everything else, joan provides Kinovea big_smile
Best regards,

- the repairman will never have seen a model quite like yours before -

5 (edited by joan 2018-Nov-16 10:42:00)

Re: Custom (human) drawing tools

I also stumbled upon that page you linked from U Ottawa yesterday, I think the original Dempster parameters are in a paper from the 50's and this page is an adaptation for 2D. But they aren't really saying how they transformed the original parameters. Will check the Winter book in reference, I have it somewhere.

edit:
I uploaded the relevant table from Winter book (Biomechanics and Motor Control of Human Movement) here:
Table 4.1 - Anthropometric data.
The U Ottawa page for 2D studies is using the same parameters for relative segment weights and segments COM.