Spot Following


Well-Known Member
Premium Member
Fight Leukemia
Aug 15, 2008
FWIW, GPS is not accurate enough for such a job, and easily blocked by structures. BlackTrax uses infrared so I guess it's based on similar technology to the Wii remote.


Well-Known Member
Dec 17, 2014
Caterham, Surrey, UK
Yes, GPS might be able to just about tell if you're roughly SL, SR, US or DS (on a big enough stage), but closely enough to accurately track, no. You need resolution down to a few inches; publicly available GPS is, what, accurate to about 5 yards? Military high resolution GPS would just about do it, but even then they're only roughly 6 feet accurate most of the time and you still have to be able to see the satellites, and (indoor) theaters aren't renowned for having a clear radio view of the sky.


Well-Known Member
Mar 18, 2019
Such gizmos do exist, trackers are worn by the talent and as they move the lights follow them, but they ain't a dime a dozen (and they're still not as good as an experienced follow spot op).
Cirque du Soleil is one group that makes use of them (at least for some of their productions). The YouTube video of "Behind the Curtain of Crystal" they posted recently makes some mention of the technology they used: IR transmitters on the performers, and an array of IR-sensitive video cameras scattered around to detect them. Besides light tracking, they also used the tracking system to procedurally generate vidoe projections on the fly that follow and interact with the performers, which I found doubly impressive. That's a lot of stuff to do, involving multiple systems (the tracking cameras, the tracking software that figures out the position from them, the video generation software, the projection mapping, and then getting the video to the projectors), all requiring fairly low latency. Needless to say, I wouldn't expect any school or community theater production to be able to afford access to this sort of technology at present! Maybe some day....

They've posted maybe a half dozen behind the curtain videos over the past months and all of them have had some interesting technical theater and production details. There are also a bunch of performance videos posted, if you're wondering what you could possibly do to fill your your copious free time.

Randy Worden

Jul 4, 2016
Big Bear Lake, CA
I just posted this in the ECT Connect forum but then realized it is not a specific EOS question so putting it here to a wider audience:

So bottom line: how do we get two spots to move slowly from A to B in a controlled manner but in a variable time?.
I actually did something very similar last year on my Etc EOS ION. I’ll describe what I did to give some context then provide a suggestion on how you could set up your solution.

<I>Note: I am going from memory on this, since my console is locked up in a dark theater until God-knows-when...</I>


I had to follow a singer as she walked around the stage, but I could count on her always hitting her starting mark. Grant you, this wasn’t a perfect solution And I wouldn’t plan on using this method for a regular “follow-spot” solution, but it should work great for your situation.

Now, for this solution to work, you have to remember that; when you bring a submaster down from full, it will go down from whatever level you set in the submaster to the fixtures’ Home state.

For intensity it’s easy to see that if you set the submaster to control fixture 5 up to 80%, then when you raise the sub to full, the lamp glows at 80% and as you lower the sub to 0, the lamp returns to it’s home state (0%).

A moving light requires a bit more thought and planning. When the sub is at full, the fixture will move to the position you programmed into the submaster (say, fixture 5 pointing USR). As you lower the submaster, the fixture will move towards its home position (usually, all the way to one extreme or another, or dead center, depending on your defaults).

To set up my “follow spots”, I have to set the home positions inside the fixture definition. I set the home X-value as the leftmost position (HL/SR proscenium), and the home Y-value as the lowest position DS I will want to move.

Then, in submaster 1, I program only the X-value of the other extreme position opposite of the home position (HR/SL proscenium), and in submaster 2, I program only the Y-Value of the back wall or US Cyclorama. If I turn up the intensity with the light pointing DSR and move both submasters from 0 to full, the light will move from DSR to USL. By moving these two submasters I can Mimic a follow spot.

My cue contains the location and intensity of the starting position and Automark handles the initial move to the starting location in the previous cue.

Again, this was far from a perfect solution. First of all, the sub masters had to be positioned at the correct level to match the beginning cue, otherwise the first move of the submaster causes the light to shoot over to that location. For example, if the subs are all the way down and your cue moves your fixture to CS, the moment you move the submaster, the light will shoot to home position.

Second problem was, that it takes really fine and smooth movement of the submaster otherwise the light flys across the stage and/or overshoots the target easily.

As for YOUR situation: I would suggest that you set you fixture definition to locate the fixture to your starting point when you hit “Home”. Then, put your level and starting position of the light in your cue. You may be able to use one submaster where you put your ending X & Y positions (Make sure there is no other data like levels).

Once you take the cue, slowly move the submaster up to follow the performer to their final position. Have a 2nd cue fade out the spot and perform any other actions.

I hope this points you in a useful direction.

Break a leg and keep healthy,