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Probes are model components that perform vector measurements on an OpenSim model during a simulation. These measurements can then be output to an external file using a ProbeReporter analysis. This is a valuable new feature of OpenSim as it exposes the time history of an unlimited variety of model parameters to the user during a simulation. Currently available Probes include:
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- ActuatorPowerProbe: measures the power of an OpenSim Actuator.
- JointInternalPowerProbe: measures the internal power of an OpenSim Joint.
- SystemEnergyProbe: measures the total energy state of a model.
- Umberger2010MuscleMetabolicsProbe: measures muscle metabolic power (based on Umberger et al., (2003 and 2010)) -- Available in OpenSim 3.1 and later
- Bhargava2004MuscleMetabolicsProbe: measures muscle metabolic power (based on Bhargava et al., (2004)) -- Available in OpenSim 3.1 and later
OpenSim also includes additional probes to measure the force and power of an OpenSim Actuator and Joint internal power; however with the addition of OpenSim Outputs as of OpenSim 4.0, we recommend using the Outputs and OutputReporter instead of the Probes. See Analyses.
In addition to querying a model value, Probes can apply an operation to that value. Available operations in OpenSim 3.0 areinclude:
- “value”: No operation performed: this just returns the probe input value.
- “integrate”: Returns the integral of the probe value. Note that you must specify initial conditions.
- “differentiate”: Returns the derivative of the probe value.
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| Probe Input (including the desired 'operation') | ----> | Apply user selected 'gain' | ----> | Probe Output (via ProbeReporter Analysis) |
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The combination of different operations and different Probe components provides a rich set of data that can be extracted during a model simulation. For example:
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Specifying Probes in the OpenSim Model
Adding and Deleting Probes in the GUI
| Starting with OpenSim 3.1 you You can add and delete probes in the OpenSim GUI. To add a probe:
Specify the probe's parameters:
See the section below for more information about the parameters of a probe. To delete a probe, Right click on the probe of interest in the Navigator panel and select Delete.
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Using probes with the gait workflow? Please note that the Residual Reduction Tool makes a copy of your model and then removes all the actuators. If you've added probes to the model that rely on any of these actuators, OpenSim will disable them. If you run RRA and choose to Adjust the model, you'll need to re-enable your probes. |
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To get a list of required properties for a specific probe, use the XML browser or Property Editor in the GUI, type “analyze –PI <ProbeName>” from the command prompt or see the Doxygen for Probes.
Example XML code (valid for OpenSim 3.1) for some example probes:
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| language | html/xml |
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| title | Probe ModelComponent Examples |
| collapse | true |
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ProbeReporter
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Analysis (for reporting probe outputs to file)
When Probes are specified in an OpenSim model, they will be automatically evaluated during a simulation. However the probe output values will not be reported to file unless a ProbeReporter analysis is also attached to the simulation (more information on OpenSim Analyses). The ProbeReporter 's job is to cycle through all 'enabled' Probes in the model at a user specified simulation step interval, and report their values to an external file. Note that an Analysis is not a ModelComponent, and therefore not specified as part of the model. Rather, OpenSim analyses are set up as part of the tool that is invoked to perform a simulation. E.g. inside the RRA/CMC/Forward setup file under <AnalysisSet>.
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See the Probe Doxygen for more details on using the API to create custom Probes.
ap over it remain mostly parallel to the same axis throughout their range of motion, then the axial method will produce well-behaved wrapping paths.
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Next: OpenSim Models Previous: Joint Reactions Analysis |
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