Search found 166 matches
- Thu Oct 03, 2024 10:39 am
- Forum: OpenSim
- Topic: GCVSplineSet errorVariance
- Replies: 8
- Views: 1863
Re: GCVSplineSet errorVariance
I missed this, the notifications from SimTk forums don't always arrive. This reply is very late, but may still be useful for someone. When you use GCVSpline, you generate a spline from the (X,Y) data once, with a specified smoothing setting (the variance parameter). The spline is stored as a series ...
- Tue Sep 03, 2024 7:43 am
- Forum: OpenSim
- Topic: Moment arm calculation of OpenSim
- Replies: 4
- Views: 672
Re: Moment arm calculation of OpenSim
The paper cited by Mohammadreza is very good, but there is one error in the paper that I would like to point out (in case it causes confusion). When a model has moving muscle points, the paper says that equation (1) should be used instead of equation (3). This is, however, not correct. Equation (3) ...
- Fri Jan 12, 2024 1:15 pm
- Forum: OpenSim
- Topic: error in inverse dynamics
- Replies: 9
- Views: 2776
Re: error in inverse dynamics
The spatial registration between raw motion capture data and force plate is correct, the center of pressure is exactly were it is expected and not 0.4 meters off. I plotted the horizontal position of COP and a few markers in the lower right leg and foot. Untitled.png The next thing to check would be...
- Fri Jan 12, 2024 9:00 am
- Forum: OpenSim
- Topic: error in inverse dynamics
- Replies: 9
- Views: 2776
Re: error in inverse dynamics
I plotted your data. Untitled.png The joint moment is close to 400 Nm at the peak, which is far too large indeed. The GRF at that time is 1000 N (which is normal), so this means that the center of pressure is about 0.4 meters from the ankle joint. Unless your subject is wearing skis, that is not pos...
- Tue Jan 09, 2024 11:07 am
- Forum: OpenSim
- Topic: GCVSplineSet errorVariance
- Replies: 8
- Views: 1863
Re: GCVSplineSet errorVariance
Mohammadreza, You probably meant to say "the GCV mode can be implemented ... if I set the errorVariance to a negative value". If you know the variance, you can specify it as a positive value. And the larger that value, the more difference the spline allows between smoothed and raw data. So more smoo...
- Mon Jan 08, 2024 12:41 pm
- Forum: OpenSim
- Topic: Simulate accelerometer on tibia
- Replies: 2
- Views: 881
Re: Simulate accelerometer on tibia
Just be aware that an accelerometer does not measure acceleration. The marker acceleration is the acceleration expressed in the global reference frame. An accelerometer measures global acceleration but expresses it in a local reference frame (the sensor axes). And there is an effect of gravity. The ...
- Mon Jan 08, 2024 12:30 pm
- Forum: OpenSim
- Topic: GCVSplineSet errorVariance
- Replies: 8
- Views: 1863
Re: GCVSplineSet errorVariance
I have a lot of experience with the GCV spline code (received it in 1985 on a 9-track tape!). The Fortran source code is still available on Netlib at https://www.netlib.org/gcv/gcvspl. After the first page or two, look at the "SUBROUTINE GCVSPL" with good technical information. There is an accompany...
- Tue Nov 21, 2023 3:12 pm
- Forum: SCONE
- Topic: GaitMeasure calculation
- Replies: 6
- Views: 1810
Re: GaitMeasure calculation
That seems to work! The step velocity value is now consistent with the horizontal speed of the pelvis. Result = 0.667518 CompositeMeasure = 0.667518 Gait = 0 <- 100 * (0.0162636 > 0.05) step_velocity = 1.06426 step_count = 72 Effort = 0.618483 <- 0.1 * 6.18483 effort = 16107.5 distance = 34.943 DofL...
- Tue Nov 21, 2023 1:44 pm
- Forum: SCONE
- Topic: GaitMeasure calculation
- Replies: 6
- Views: 1810
Re: GaitMeasure calculation
Thomas, Thanks, that is amazing that you were able to fix that so quickly. I will test it immediately if you give me install instructions. I agree that the GaitMeasure should become zero during the optimization so that in the end only the effort is minimized. About the font, yes, it's on Windows. My...
- Mon Nov 20, 2023 9:12 am
- Forum: OpenSim
- Topic: Knee joint definition issues in gait model
- Replies: 2
- Views: 894
Re: Knee joint definition issues in gait model
Johannes, The knee is a little different in this model, because the axis of rotation translates relative to the femur. This translation is coupled to the rotation (i.e. a function of knee_angle) and you can find this in translation1 (x) and translation2 (y). Translation y varies from -0.39 to -0.42 ...