Things to remember when filming for Planer Motion Tracking

PhilWessonPhilWesson Website User Posts: 241 Enthusiast
Hey everyone~
So a couple of days ago, just as I finished up work, I took my camera outside of my office, and filmed a few tracking shots, with the intention of tracking them in Mocha for practice. It had rained recently, so there were some puddles on the ground. 
I had the foresight to film at a higher shutter speed, to minimize motion blur, but I didn't know how else I could prepare for the shoot in order to get the best track out of mocha. Had I known that the reflections in the puddles were going to cause so much of an issue (as well as the reflections in the windows of my office building), I would have choses a different location. 
I also shot in cinestyle, which some of you may know flattens the color and contrast to allow for more color information when grading. As great as that was, it didn't really do me any favors, as there were fewer variations between colors for mocha to track. 
I've pretty much given up on the footage that I shot, but I thought I'd ask here:
What things should we keep in mind when we know that we'll be using Planer Motion Tracking? After watching the last two tutorials, I know what I can look out for to get a good track, but I'm wondering if there are preemptive things we can do on set to avoid common issues by the time we're ready to do post.

Comments

  • BrianJohnsonBrianJohnson Website User Posts: 83
    edited May 2013
    I remember to look for good ground & wall surfaces to track. Stuff with good contrast and low reflection.  Asphalt roads tend to work good if they are close to the camera and are in focus.  
    I also have printed out some Black and White checkerboard patterns on letter sized paper and taped a couple to a wall or placed some on the ground.  Then filmed the scene.  Then I can use those as tracking points. I can then add a 3d plane with the wall texture/ground texture (taken from a still photo of the original scene) and cover up the black and white checkerboard.  
    I stumbled across this idea by accident when I was getting test footage. I filmed the kids play area and there were books on the floor. They worked great for tracking.  Good contrast in the cover art, and they are easy to align the plane with because of the square/rectangular shape. 

    This is similar to what I use for the checker pattern.checker_pattern_postcard-r66f635f4cf5349
  • PhilWessonPhilWesson Website User Posts: 241 Enthusiast
    Thanks Brian, that's a great idea!
  • AxelWilkinsonAxelWilkinson Staff Administrator, Imerge Beta Tester, HitFilm Beta Tester Posts: 5,242 Staff
    edited May 2013
    Usually motion blur won't really cause many issue with mocha, that's one of the many advantages of planar tracking over point tracking.  It doesn't matter what sort of tracking you are using though, reflections have to be avoided, because they don't accurately represent the surface being tracked.  The surfaces being reflected are at different distances from the camera and the angle of instance is likely to change as the camera moves, resulting in perceived movement within the reflections.  And incidentally, all of the footage I shoot for the tutorials I'm doing is shot with a Canon DSLR using the Cinestyle profile.  The shot from Extraction Protocol which I used in the first tutorial is an exception.  But the flattened colors that Cinestyle creates aren't likely to cause an issue, as long as you are tracking planes that have some texture to begin with.
    Puddles on the ground aren't a problem, as long as you hold out the areas inside the puddles, so you only track the ground between them.  Similarly with windows, unless the building is entirely glass, with not framing between the panes, then you can hold out the windows and get a decent track.  Throw up a frame of the footage, and I'll be happy to offer suggestions for where I would place the splines.
    Have you watched any of Imagineer System's videos on shooting for planar tracking? They have dozens of great videos that cover pretty much every aspect of using mocha on their site.
    http://www.imagineersystems.com/videos/how-to-shoot-for-planar-tracking/view?searchterm=camera%20work
  • PhilWessonPhilWesson Website User Posts: 241 Enthusiast
    Axel, I actually have that page up and ready to watch as well. You replied to my comment on youtube saying pretty much the same stuff, didn't know about the fact that you're using cinestyle, so thanks for the clarification.
    I'm assuming that when I make my splines in Mocha, I can use another spline to essentially cut out the puddles, so they're not tracked? 
    I'm at work right now, and unfortunately my footage is on my home computer, but I'll post it in about 30 min. Thanks for agreeing to take a look at it.
  • AxelWilkinsonAxelWilkinson Staff Administrator, Imerge Beta Tester, HitFilm Beta Tester Posts: 5,242 Staff
    edited May 2013
    Yes, you use another spline, but make sure that you use the Add Spline tool, so the new spline is on the same layer as the first one.  So, draw the main spline that contains the ground plane, then switch to the add spline tool, and draw around the inside of each puddle  If you end up with two layers in the Layer controls, then something went wrong.  Turn on the Mattes in the top toolbar and you can see exactly which area will be tracked.
    Because I want the tutorials to be as relevant as possible, I try not to use any special gear while filming.  Mainly its a Canon DSLR with an affordable lens, either shot handheld or on a tripod, using Cinestyle profile.   Many of our users aren't using professionally stabilized footage shot with super expensive cameras, so that's not what I use for the tutorials.
  • PhilWessonPhilWesson Website User Posts: 241 Enthusiast
    Axel, here's a frame from the footage that I was referencing.
    frame.png?format=1000w
    I'm using a Canon T3i with cinestyle, so I'm assuming we're somewhere in the same boat. I'll have to try again with the Add Spline tool. However, looking at the still) and especially the ground plane, which has very little contrast, what are your thoughts?
  • AxelWilkinsonAxelWilkinson Staff Administrator, Imerge Beta Tester, HitFilm Beta Tester Posts: 5,242 Staff
    Thanks.  I should have asked what direction the camera was moving as well, but based on that frame, here is where I would place splines to start with:
    [attachment=581:Splines.png]
    The small amount of reflections within the ground spline likely wouldn't be an issue, but you could create a holdout around them if need be.  Make sure you include the bottom edge of the half-wall below the building, as well as the dark edge of the walkway at the far end of those parking spaces, and that combined with the parking lines should give mocha lots of info to work with.  The edges of the building are quite clear as well, so that upper spline should be able to lock on quite nicely.  And both locations make it fairly easy to align your tracking surface and grid, since they have rectangular lines you can follow.
  • PhilWessonPhilWesson Website User Posts: 241 Enthusiast
    Axel, 
    Funny, that was exactly where I was putting splines. The footage is a bit shakey, and I think the focus could have been a bit better. that being said, I was doing a tracking shot from left to right, and panning up slightly as I was going. I'll give it another shot with the Add Spline tool. 
    Are there any other shooting for planer tracking tips that you use?
Sign In or Register to comment.