Understand how to use Vicon for Collecting Data

[kouroshD]

I wanted to use Vicon setup for collecting data. However, it is not clear to me what are the steps in order to properly collect the data, e.g.:

• if calibration is necessary every time we use the setup
• Link to a video that explains how to use the software (I saw there are some in youtube, but you may know a good one that explains everything we need)
• running the yarpserver, and the yarpdevice.

Thanks.

@Nicogene @aikolina @prashanthr05 @GiulioRomualdi

[Nicogene]

Hi @kouroshD ,

The calibration step is not necessary unless you don't notice some odd measurements.
For using this device you have to follow these steps - > https://github.com/robotology/yarp-vicon-bridge#using-the-vicon-setup, in particular the vicon device has to be launched after running the Nexus on the workstation.
Unfortunately Nexus it is not the most user-friendly software, I used it very long time ago, the latest it used it was @aikolina, maybe she has some useful links and hints.

[prashanthr05]

if calibration is necessary every time we use the setup

These were some advice about calibration of the Vicon System from a Technician who briefed us on using the system,

• The Technician advised that its good practice to calibrate the Vicon System every session it is being worked with.
• In case of an earthquake, definitely must do calibration ;D
• If we see phantom speckles after calibration, then the reconstruction from the Vicon is not good, which means the system needs to be recalibrated.
• If there are different illumination conditions from one session to another, this can simply be handled by tuning certain parameters in the Nexus application.
• In case the setup was disturbed during a session, and we have to conduct only one last trial, we can still proceed with the acquisition and calibrate the system after to reuse the calibration parameters on the last dataset. (not recommended but useful in unavoidable situations)

Link to a video that explains how to use the software (I saw there are some in youtube, but you may know a good one that explains everything we need)

I am copying here some of the information collected by @aikolina regarding the usage,

• Nexus General Workflow 1: Preparing your system (System Set-up, Masking, Calibration)
  https://www.vicon.com/support/faqs/?q=nexus-general-workflow-1-preparing-your-system-system-set-up-masking-calibration

• Nexus General Workflow 2: Capturing Data (Calibration and Dynamic Trials)
  https://www.vicon.com/support/faqs/?q=nexus-general-workflow-2-capturing-data-calibration-and-dynamic-trials

• Why should I complete a subject calibration within Nexus?
  https://www.vicon.com/support/faqs/?q=why-should-i-complete-a-subject-calibration-within-nexus

• How do I determine a marker Status in Nexus?
  https://www.vicon.com/support/faqs/?q=how-do-i-determine-a-marker-status-in-nexus

Video Tutorials
https://www.youtube.com/playlist?list=PLxtdgDam3USUSIeuO6UloG3ogPsFNtEJS
Potentially interesting videos (IMO):

• System Preparation
  • Calibration
• Subject Preparation
  • Building a Custom VST
  • Using a Custom VST
• Capture
  • General Workflow for Capture
  • Data Capture Pane
  • Creating and Using Monitors
• Data Processing
  • Data Processing
  • Gap Filling

[kouroshD]

I found specifically the following videos very useful for the naive users: (thanks to @aikolina )

• Nexus 2 tutorial - General Workflow for Capture
  

• Nexus 2 tutorial - Building a Custom VST
  

Some other points: (based on my understanding, so I am not sure about them)

• we can have only one subject (in the resources pane) when recording the data.
• Each subject is composed of different segments or links.
• After identifying the segments, we can connect them using different joints types (linking the segments).
• The root segment is connected to the vicon_root via a free joint. have look in the following documentation https://docs.vicon.com/display/Nexus25/Link+segments
• In theory, we should be able to have several subjects here (!), and connect them via a free joint to a root segment.
• We should be able to make segments and connects them via a free joint. So they can move freely in the workspace (however, when I tried it, it was working some times and not working some other times.).

[kouroshD]

Also, we can export the logged data by Vicon with ASCII operation, i.e., .csv, .txt.
https://docs.vicon.com/display/Nexus25/Configure+file+export+pipeline+operations#Configurefileexportpipelineoperations-ConfiguretheExportASCIIoperation

However, the timing is not the machine time.

[traversaro]

However, the timing is not the machine time.

Which time they use? Can we find an offset w.r.t. to the "machine time"?

[kouroshD]

However, the timing is not the machine time.

Which time they use? Can we find an offset w.r.t. to the "machine time"?

To be honest, I do not recall it now precisely, but as far as I remember the initial time is either the time we start the software or the time we start logging of the data.

Can we find an offset w.r.t. to the "machine time"?

I am not sure if it is possible. I have not seen a parameter in the Vicon software to set this.

[Nicogene]

This issue contains a huge amount of useful information, that once closed risks to be lost.

It would be great if we can integrate it in the README 🚀

[Zhongheng-H]

Hi,

I am currently trying to export the .csv files with machine time, also with millisecond precision. But as you said, I cannot find any setting to export this. Have you found out the solution?