Solving Nodal Pans in PFTrack
Nodal pans, where the camera is mounted on a tripod, provide a specific challenge to 3D camera tracking, due to the lack of parallax in the shot. In this tutorial, you will learn what that means when solving your camera, and how to use reference frames in order to extract 3D information from nodal pans. This tutorial provides an introduction to the User Track node, and demonstrates a technique that can also be used to solve multiple moving cameras into the same scene.
– Import The Stills
– Create The User Track Node
– Create a User Tracker
– Track The User Tracker
– Place The User Tracker In The Reference Images
– Create Additional Trackers
– Create The Camera Solver
– Set Up The Camera Solver
– Review The Solution
01. Import And Review Clips
02. Solve Without Reference Frames
First try and solve the camera the usual way. Drag the thumbnail from the Media Bins into the Tree View, and create an Auto Track node and make sure it is connected to the clip. Leave the settings as they are and click Auto Track. As you look at the automatically created trackers you can notice that their paths are (almost) identical, no matter whether the feature is close to the camera or further away. This indicates a lack of parallax.
A good way to check for parallax is to select one tracker and press the Centre View button. This will keep the selected tracker in the centre of the Cinema. Then scrub forwards and backwards to see how the other trackers move relative to the selected tracker.
03. Track With Reference Still Images
Import The Stills
Create the User Track Node
Create a User Tracker
Track the User Tracker
Place the User Tracker in the Reference Images
You can use the Current clip menu to select between the different inputs of the User Track node. Select the first reference image, PFTChurchPan_ReferenceA0, from the menu. Click and drag the right mouse button to pan, and the middle mouse button to zoom to locate the same white patch in this image. Then left click to place the tracker at the same spot. Adjust the placement in the Tracking Window if necessary.
Your trackers table should list one tracker, Tracker0001, with PFTChurchyard_Pan and PFTChurchyard_ReferenceA listed in the Clips column. This means that the same tracker is placed in both the clip and the reference image.
Create Additional Trackers
Place additional trackers as shown in the screenshot above. Don’t forget to place them in both the reference images as well. A minimum of 6 trackers are needed per frame, but it is recommended to have 8 or more.
If you run into difficulties or want to compare your trackers, PFTChurchyard_Trackers.txt in the PFTChurchyard_Trackers.zip file contains the tracker locations used for this tutorial. Simply click Import in the User Track node and open the file to load these trackers into your node. Make sure to have the clip and reference images connected to the node as outlined in this tutorial, with the movie clip in the first input, PFTChurchyard_ReferenceA in the second and PFTChurchyard_ReferenceB in the User Track’s third input before loading the trackers from the text file.
04. Solve The Scene With Reference Images
Create The Camera Solver Node
Set Up The Camera Solver
Switch to the reference frames in the Current clip menu. You will notice that the Helper checkbox has been automatically checked. This means that these inputs will be used to assist to solve the main camera in the first input. Click the Help button to open the Camera Solver’s reference help page and scroll to the Helper Frames section to read more about using reference images as helpers.
Return to the movie clip and click Solve All.
Review The Solution
05. Test The Solution
In this tutorial you have learned how to use reference still images to make up for the lack of parallax in some shots, for example where the camera has been mounted on a tripod. The resulting scene not only contained the necessary 3D information for the movie camera, but also the camera positions of where the reference images had been shot.
You can use the same technique of placing user trackers in more than one shot to solve multiple movie cameras into the same scene, when the use of photogrammetry is not an option. However, moving cameras cannot be used as helper frames, but would be solved after the main camera.