So welcome to my first tutorial on Nuke. I hope I can continue this monthly, so that you will check this site regularly! Why have I chosen Nuke and why the Reconcile 3D node for my first tutorial ?? Well this is pretty easy to explain. Nuke is my favorite compositing tool, first because of its speed and flexibility, and second because it rocks on my macbookpro! The reconcile 3D node was chosen, because it saved me so much time, that I spent in Shake tracking objects even though I had a 3d camera.
So now let's start: The reconcile 3D node is usually used when you need to have a 2D transformation on an object, that exists in 3d. Let's say you have a pan and tile shot and on one of your images there is a lenseflare. You build your panorama inside the 3d space in Nuke, and set up a camera. Now the problem is, that your cam pans over the image with the flare, and everybody will notice, that this flare is 2d. So you want to add a lensflare in Nuke, that moves realistic to the camera. What you can do now is add a locator and use your reconcile 3d node, to calcualte the locators position in 2d, and link this information with your lensflare node. A locator inside Nuke is usually an Axis node, found in the 3d menu. Now let's assume that you have a shot, where you need to add 3d or 2d elements. In a production pipeline the first thing usually done is a 3d matchmove. In the image below you see the matchmoved camera with 2 locators inside Maya. The advantage here is, that the locators are from the matchmoving application, and therefore have the right position automatically.
I can now select one locator and export a .chan file with the script found on highend3d . The same thing is done with the camera. Back in Nuke create a Camera and an Axis node and import the .chan files.
The most important tip here is, that your Maya camera is in inches and Nuke calculates in millimeters. So you definitely have to change your vertical and horizontal aperture so that your Nuke cam will match the Maya camera.
Then create a reconcile 3D node and connect your cam into the camera input and your axis in your axis input. The image input is for the image you want to move based on the Axis position in relation to the camera movement. So when everything is connected click on create keyframes. The image that is connected in the image input will then automatically follow the position, where the locator was in your 3D scene. You can add a corner pin for instance to the image above in order to match it to a certain area in your shot. You can use the reconcile3D node to move the image, but you can also link the translations to a 2D transform or 3d transform node, or whatever node you like. In the image below I linked the reconcile3D node to the position of the Flare node.
I think it is clear that this is a wonderful and fast way for matching elements without the need of tracking in your comp application. This finishes my first try of a Nuke tutorial. I hope it is of some help, and you will give me some feedback, whether I should continue with this short tips.