From the course: SynthEyes Essential Training (2015)

Overview of lens distortion

- Lens distortion is an important factor in camera tracking. Understanding how it works will help you to get a better cam result. In general, you should remove lens distortion before tracking, but in some situations you may not need to depending on the final result. SynthEyes works and real world geometry like most 3D software, lens distortion can change the depth, and location of real world objects, and distort the geometry of real world objects. If you look back to the video on camera basics, a similar effect happened when just changing the focal length. Here I have an example where I track the same footage, with the same points, the same focal length, and the same coordinate system. But camera one has been undistorted, and camera two has not. If we go to the quad view, you can see this more clearly. The green X's represent the undistorted plate, and the light blue X's represent the distorted plate. You can tell that the green cluster here is the same as this light blue cluster, and you can see the difference in 3D space. So let's say we had to replace this entire building with a CG building, that needs to be relight in real world lighting. If we were going to do that, we should definitely undistort the plate, so that we have real world geometry that will work with lighting in a 3D software package. But if for example, we just need to replace this sign we may not have to undistort the plate, because it wouldn't really matter if the geometry was a little distorted. Instead of having a flat sign, it might be a little bit angled, but if it's just the sign and you don't have to relight, you may not need to undistort the plate. So take that into consideration, when you're working through your shots. But in general, you should undistort the plate if you want an accurate cam result. Distortion can cause a lot of problems in match moving, identifying lens distortion and finding a workflow is an important part of 3D tracking.

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