How do I make a movie that shows tracking of objects over time?

Everyone loves a good movie and a question that I am frequently asked is how I make movies in Volocity that show tracking of objects as they move in time. These movies help to give a more detailed insight into biological processes and they are great for incorporating into presentations – my students love them! In this tip I am going to show you how I would make a movie similar to the one shown below.

Open your dataset and switch to the Measurements View. You will first need to create a measurement protocol to locate the objects of interest in your dataset by dragging and dropping tasks in the task list into the measurement protocol. Make sure that your protocol identifies objects as accurately as possible in each timepoint as this will be essential for the tracking algorithm.

To track the movement of your objects through time, add the ‘Track Objects’ task to the measurement protocol. The tracking algorithm uses the centroid measurement for each previously identified object to determine whether there is any movement of objects over time. Tracks are generated by connecting the centroids so as to trace the path of a moving object. The track objects task will always place itself at the bottom of the list of tasks in the protocol since objects must be found before they can be tracked.

An important thing to remember is that, by default, the Measurements View only shows the protocol as applied to the current timepoint. However, measurements of tracks will only be generated if all the timepoints are measured; therefore you should select ‘Measure All Timepoints’ in the Measurements menu. This will apply the protocol to all timepoints and track the centroid positions of the objects found. You should now see tracks appear in the Measurements View.

To alter how the tracks are measured, click on the cog icon on the Track Objects task (highlighted below) to access the secondary dialog for the Track Objects task. Select the appropriate options and then click OK to close the dialog.

You may want change the appearance of your objects and tracks depending on what you would like to visualize in your movie. To do this, use the 'Feedback Options…' command in the Measurements menu. The dialog box that opens has multiple tabs for different types of measurements. To make a movie that shows objects moving along their tracks over time, I click on the Tracks tab and then select to show the objects in the current timepoint only.

The track measurements that are generated are added to the Measurements Table in the Measurements View along with the list of objects that you have identified. You can use the quick filter menu to view just the track measurements.

Selecting individual track row(s) in the measurements table will highlight only those selected tracks in the Measurements View. This makes it easier to examine the trajectory of individual objects in more detail.

Now switch to the Image View by clicking on the Image tab at the top of the page. In this view you can see the tracks that you have selected previously, overlaid onto your data. If you now play through your timepoints using the time navigation controls, you will see the objects moving along these tracks over time.

When you are satisfied with this view, you can create a movie by simply selecting ‘export’ from the file menu. Name the file and select a folder for the exported movie. You should then select one of the 'View as...' options, e.g. "View as AVI Movie", "View as WMV Movie" or "View as Quick Time Movie" (if you have QuickTime installed on your system).

Now you have an eye-catching movie to impress your friends and colleagues!