For trials where the subject starts outside the volume, moves into the volume and then exits, cropping the start and end of the trial removes unwanted frames where the subject was not fully in the volume.

Before you fill gaps in your trial data, it's a good idea to remove these start and end frames as they are likely to contain large gaps and other invalid data. You can do this automatically while capturing (see Trigger data capture on labeling percentage), or for trials that have already been saved, you can crop trials manually or run a pipeline operation to do this automatically.

Cropping a trial affects only the .c3d file. The raw files remain unchanged.

Manually crop a trial

You can use tools on the time bar to remove unwanted frames at the start and end of your trials.

To manually crop a trial:

1. Ensure the required trial is reconstructed and labeled (see Reconstruct and label movement trials).
2. On the time bar, do one of the following:
   
   • Move the range indicators (blue triangles) to exclude the unwanted frames at the beginning and/or end of the trial; or
   • Right-click and then click Set Region-of-Interest. In the Set Region of Interest dialog box, specify the Start Frame and End Frame.
   The gray shaded area represents the cropped frames of the trial.
3. Right-click on the time bar and click Zoom to Region-of-Interest.

You can now fill any remaining gaps.

Automatically crop a trial

Nexus can save you time and effort by automatically determining the first and last frame where the subject is fully in the volume

When you run the autocrop operation, Nexus automatically zooms the time region of interest to the points where the subject first fully enters and then leaves the volume.

To set up auto-cropping:

1. Ensure the required trial is reconstructed and labeled (see Reconstruct and label movement trials).
2. In the Tools pane, click the Pipelines tab and in the Available Operations list, expand Events & Timebar.
3. Double-click the Auto Crop Trial pipeline operation to add it to the current pipeline.

   

4. In the Current Pipeline list, click Auto Crop Trial and in the Properties pane, ensure that the First and Last Frame options are set to the beginning and end frames during which the subject enters and leaves the volume.
   
5. Set the Start and End (%) options to the required minimum percentage of markers (ie, the percentage of markers expected from the total number of markers in your subject's labeling skeleton) that must be labeled in each case.

   

6. If necessary, adjust the Frames Required to set a minimum number of frames where the Start % criterion must be met. This is helpful if early single frames of data meet the %, but the point at which the trial is intended to start (ie, the point at which the % is maintained over a number of frames) is later in the trial.
7. Run the Auto Crop Trial operation.
   The trial is automatically cropped to the frames you have selected.

You can now fill any remaining gaps.