In the last part of my 3D integration VFX tutorial I took you along on an actual shoot to discuss the things to keep in mind when filming a scene for 3D integration.
Today I will talk about how to use the 3D camera tracker in Adobe After Effects CS6 to extract camera movement information and export that information into your favourite 3D program :)
After Effects 3D Camera Tracker Tutorial – 3D Integration VFX Part 3
Do I need to use the 3D camera tracker?
Using the 3D camera tracker to analyse your footage and extract camera information only makes sense if your camera is moving during the shot. If you have a locked down shot (fixed camera position) and assuming you wrote down all the information to replicate the scene in your 3D program as discussed in the last part, you do not need to use 3D camera tracking and you can move on to the next part of this tutorial :)
However, in the UFO scene we filmed, the camera executes a pan and a tilt up towards the sky so we will have to track our footage.
Using the 3D Camera tracker
Before we get to our UFO scene, let me first show you how to use the 3D camera tracker in a normal situation. I have a scene here of me walking with my camera through a street in Melbourne.
To apply the 3D camera tracker, simply locate the ‘3D Camera Tracker’ effect in the Effects & Presets panel and apply it to your footage layer. The tracker will immediately begin analysing your footage in the background.
The 3D camera tracker is now processing your footage frame by frame and applying 2D track points to trace the movement of distinct visual elements in the scene. Once it has completed this task, it will solve this cloud of 2D track points and their movement to reverse engineer the position and movement of the camera. It will also convert the 2D track points into 3D track points using the calculated depth information.
This can take a while depending on the resolution and length of your footage as well as the power of your computer.
While this is going on, let’s have a quick look at all the parameters availale in the 3D camera tracker.
I don’t find myself changing these parameters often as the tracker usually does a pretty good job all by itself. However, it’s good to know what these settings are useful for in case you do get into a more tricky situation.
At the very top, the effect will show you a progress indicator to tell you how much longer you will have to wait until analysis is complete.
Below this indicator you can specify the shot type.
- Fixed Angle of View. Use this option if your focal length did not change during the shot and you are fairly confident the tracker will detect it automatically
- Variable Zoom. Use this option if you zoomed in/out with your camera during the shot
- Specify Angle of View. If you do not trust the 3D camera tracker to detect the angle of view automatically, you can use this option to specify it explicitly
For most of my shots, I usually just leave it on ‘Fixed Angle of View’ and I haven’t had many issues yet :)
The next option allows you to specify which track points to show.
This will only become relevant once the 3D camera tracker has finished analysing and a number of track points is displayed on top of your footage.
- 2D Source. This option will show the flat 2D track points used to trace the visual elements in your shot
- 3D Solved. This option will show the final 3D track points that were created using the calculated depth information from the 2D source
Just leave it on ‘3D Solved’ and you’ll be fine. If something goes wrong and you do not have any 3D track points, the 2D source track points will be displayed instead :)
You can also adjust the track point and the target size. The target size refers to the size of a visual bullseye helper that you will see when you hover your mouse over a tracked piece of footage. You will see that shortly. If you want to render the track points as part of the effect, you can check the ‘Render Track Points’ option.
Just above the advanced options you will find the ‘Create Camera’ button.
Once the 3D Camera Tracker has finished its work, this button will be enabled and you can click it to create a camera that imitates the movement of the camera used to film the footage.
Let’s expand the Advanced options by clicking on the twisty (triangle) to see what goodies we have in there :)
First off, you can specify the solve method used to try to extract camera and depth information from the 2D track points.
- Auto Detect. This option will automatically try to detect the best of the three options below
- Typical. This is your typical scene inluding potential camera movement and rotation
- Mostly Flat Scene. This specifies that your scene is mostly flat
- Tripod Pan. This specifies that the scene includes panning movement with a camera that was sitting on a tripod
Once the 3D camera tracker has finished analysing your footage and solving the 2D track points, you will see some results information below the solve method option.
- Method Used. Displays the solve method that was used. If you set Solve Method to Auto Detect, this will show you which option auto detect chose for you
- Average Error. This value indicates the accuracy of your tracking. It is the pixel distance from the 2D track points to the final 3D track points. A value below 1 is usually a fairly good track, a value above 1 could mean the tracking was not very spot on and you might want to adjust a few parameters and track your footage again
You also have the option to perform a more detailed analysis of your footage and suppress any warnings that are usually shown when the tracker wants to tell you that you should re-analyse your footage.