Knowledge Base

Interpolating Points

How the Center Point Is Interpolated

If you interpolate only the center points, EthoVision XT needs the coordinates of the center points for the adjacent samples in order to calculate the coordinates of the center points 5 and 6. Samples 4 and 7 are used because they are the first previous and next samples with valid center points, respectively. The interpolating range is not extended. The coordinates of the missing center points, not nose point and tail-base points, of samples 5 and 6 are calculated.

The center points of the selected samples are a linear interpolation between the first previous non-missing center point and the first next non-missing center point found around the interpolating (expanded) range.

If your track contains nose point and tail base, interpolation of center points is independent of whether you choose to also interpolate nose point and tail base. In any case, center points are interpolated first.

How the Nose Point and Tail-Base Point Are Interpolated

Nose points and tail-base points are always interpolated after the center points have been found, and their interpolation is dependent on the orientation of the non-missing nose points and non-missing tail-base points immediately preceding and following those missing samples, respectively.

Before interpolation, the missing points are indicated as a linear interpolation between the first previous and the first next non-missing points of their type. The direction of movement does not play any role in interpolation.

Consider the following example with three missing samples. First, center points are linearly interpolated. Second, for the two adjacent non-missing samples, the program determines:

• The length of the segment joining the center and the nose (or tail-base) points.
• The angle formed by this segment and the horizontal x-axis generating from the center point (this angle can be either positive or negative depending on whether the segment lies above or below the axis).

Third, the program calculates the interpolated values of segment length and angle for the missing points, using linear interpolation of the values obtained in the previous step. For example:

• If the length of the center-nose point segment for the two adjacent samples is 50 and 10 mm respectively, then the length of the three segments joining the interpolated nose points and their center points will be 40, 30, and 20 mm respectively.
• If the orientation of the center-nose point segment for the two adjacent samples is 90 and -10 degrees respectively, then the orientation of the three segments joining the interpolated nose points and their center points will be 65, 40, and 15 degrees respectively.

The second and third steps are repeated to interpolate the tail-base points.

Interpolating Points at the Beginning or End of the Track

If the range of missing points to interpolate is at the beginning or the end of the track, the missing points are not interpolated. This is also the case when you want to interpolate nose or tail-base points at the beginning or end of the track and the corresponding center points are non-missing.

Synchronize Video and Tracks

Aim

To correct the delay between video image and tracks in the various visualizations: Track Editor, Track Visualization, and Integrated Visualization.

Note: Normally you do not need to edit the offset between video and tracks, because this is calculated by the software. Follow the procedure below if you notice that the tracks are lagging behind the video.

Prerequisites

You acquired data using the method Live Tracking and Save Video.

Procedure

See Troubleshooting: Data Visualization > There Seems to Be a Delay Between Video and Track.

Manage Your Edits

Saving the Track Edits

Aim

To save edits done up to that time. If you make more changes after saving and are not satisfied with those changes, you can always recover the edits made at the point of Save.

Note: This and the following topics apply to editing tracks and manually scored behaviors.

Example: You want to interpolate points but are not sure whether the result is satisfactory. Click Save to create a copy of the track with the current edits, then do the interpolation:

• If the result of interpolation is good, click Save again. This replaces the previous track edits.
• If the result is not good, you can revert to the data of the last Save by clicking Undo.

What Is the Difference Between Saving the Experiment and Saving in the Track Editor?

Save Experiment: To save your edited tracks at any time, choose File > Save Experiment or press Ctrl+S. However, once you have saved the data, you cannot revert to the first edit. In other words, you cannot undo any save action. However, you can always return to your original track data.

Save in the Track Editor: With Save in the Track Editor you can revert to the previous set of changes. You do so with the Undo action. This is useful when you want to make sure you can recover the data after carrying out some editing.

Important: The Save action persists until you close the experiment. If you save, then make further changes to the data and close the experiment, all changes are saved, but when you re-open the experiment you cannot revert to the Save point.

Notes

• Every time you click Save, the new copy replaces the previous one. This means that you can always keep only one copy of edited data.
• The original (unedited) data are always stored in your experiment. To revert to the original tracks and discard all changes, click the Undo All button on the toolbar.
• Auto Save in EthoVision XT works like a normal Save command. Therefore, if an auto save action occurs, all changes made so far to the currently edited trial are applied. However, if you make further changes and an auto save action occurs, you can always revert to the saved copy that was made before the auto save action. To alter your auto save settings, choose File > Preferences > Auto Save.