Merging method for heatmaps
Aim
To specify how data of different tracks are merged in one heatmap.
Procedure
1.Choose Analysis > Results > Plot Heatmaps, or in the Experiment Explorer, under Results, click Heatmap Visualization.
2.In the Heatmap Settings pane, click the Show/Hide tab. Choose one of the options under Merging method.
Cumulated
Each sample in a track gets a weight equal to 1/sample rate. Therefore, the color of a pixel in the heatmap represents the total time that the subject(s) body point was at that location. Choose this option when you want to make a heatmap based on all the possible locations of the animals for a group of tracks. With this method, a subject’s position is over-represented in tracks longer than others.
Each sample in a track gets a weight equal to 1/track length. The color of a pixel represents the average proportion of a track that is found at that location. Choose this option when you want to make a heatmap that represents the average distribution for that group, and you want to compare averages between two or more groups of tracks.
example Consider two tracks, recorded at 25 samples/s. One track is 10 samples long, the other 1000 samples long. The total track duration is 1010/25 = 40.4 seconds. A subject’s center point is found at location P two times in track 1 (=20% of track 1), and 100 times in track 2 (=10% of track 2). When the two tracks are merged:
▪With Cumulated, the color of pixel P represents a total time of (2 x 1/25) + (100 x 1/25) = 4.08 s. This means that, in total, 4.08s / 40.4 s = 10.1% of the data points are at that location. The longer track has a greater weight in this calculation.
▪With Mean, the color of pixel P represents [(2/10) + (100/1000)]/2 = 0.15 = 15% of the track duration. This means that on average, 15% of the data points are at that location. Short and long tracks have the same weight in this calculation.
Notes
▪Merging makes sense when two or more tracks share the same value of an independent variable chosen as a header. For example, two tracks with the same of Treatment level = Control. If Control is one of the headers, the two tracks contribute to the same heatmap.