[Lowlimbmodel09-news] new forums and bug fixes to Two Legs HAT

[Edith Arnold]

Hello Lower Limb Model Users,

I hope you've all been having a great summer (or winter, depending on
your hemisphere).  I have two news items I'd like to let you know
about.

First, the forums were recently updated on simtk.org and they're
really slick.  The interface is much nicer and more flexible and I
think they'll be great for fostering discussion, so you should check
them out.
https://simtk.org/forums/viewforum.php?f=468

Second, two bugs in the 2-leg, OpenSim version of the lower limb mode
were recently brought to my attention, and I have posted a new version
to correct these issues.  v2.1 is now available for download.  The
bugs and fixes are:

Bug: The range of the knee_angle_r and knee_angle_l coordinate was
inappropriately increased from 0-100 degrees to 0-120 degrees in one
of the posted model versions.  I was working with this range in a
research version of the model and did not intend to post it publicly.
This model was only validated for a range of 0-100 degrees (see the
publication affiliated with the project) and the increased range
introduces errors in muscle geometry.

Fix:  In the short term, I have reverted the range of motion to 0-100
degrees in version 2.1  To avoid invalid regions of muscle geometry
please download the new version.
If you have already made modifications to the model that you'd rather
not have to re-do, reduce the range directly in your files.  This is
done by changing two lines.  Under <Coordinate name="knee_angle_r">
and <Coordinate name="knee_angle_l"> replace this:
<range>       0.00000000       2.09439510 </range>
with this:
<range>       0.00000000       1.74532925 </range>

Reload the model and check that the coordinate slider in the GUI goes
from 0-100 degrees.

In the long term, I am making several changes to the model to make it
appropriate for higher knee flexion applications and will share this
when I have validated it.  There will then be two versions of the
model available, the lower flexion one that is aligned with the
publication and a higher flexion version which will be documented on
the project page.  Check back in a few months for this.

Bug:  Wrapping surfaces were showing up as shaded, even after hiding
them in the GUI and re-saving the model.

Fix: I have changed the display preferences code for the wrapping
surfaces. I think this was a problem introduced when converting the
model between versions of OpenSim.  If you'd like to correct it
directly in your models find the VisibleObject lines under each wrap
surface and replace this:
<VisibleProperties name="">
	<display_preference> 0 </display_preference>
	<show_normals> false </show_normals>
										
	<material_name> DEFAULT </material_name>
</VisibleProperties>

with this:
<display_preference> 0 </display_preference>


Please let me know if you have any questions about these changes.  I
encourage you to post your questions and discussion in the forum here:
https://simtk.org/forums/viewforum.php?f=468
so that others may benefit from the discussion.


Best Regards,
Edith Arnold
Neuromuscular Biomechanics Lab
Stanford University
https://simtk.org/users/emarnold