Camera Matching

Topic: Camera Matching
Team Member: Everett
Location: Boiler Island
Challenge: Creating perfectly accurate scenes

For the first post on our brand new dev blog, I thought I’d explain the ins and outs of “camera matching”, a process we use to recreate the environments of Riven. At the time of writing this post, I’m deep in the process of camera matching for Boiler Island, which makes it a great time to feature it here.

Camera matching for our project is the process of taking the original images from Riven and using them to rebuild the scenes exactly as they were. It’s generally a process of trial and error, piecing together information little by little until a scene begins to take shape, matching the original line-for-line.

Ytram cave topology

The Ytram cave walkways and balcony are portrayed here in wireframe. The orange pyramid shapes are cameras matched to images from the original.

The first step in the camera matching for any new scene is always the same: find a predictable object to line up the first shot. You need an object which you know for certain is an exact shape, like a circle or a pentagon, on which to base the perspective and angle of the rest of the scene.

For Boiler Island, that shape was the boiler. Its perfectly cylindrical shape made it a wonderful fit to start matching with. The first shot is very important. You have to be sure that it’s nearly perfect before you move on to matching others. If not, the errors you made in matching the first image will greatly affect your ability to match later images, making the entire process much more of a fumble in the dark, constantly attempting to correct early mistakes. The boiler made the first shot much simpler, by supplying a clear visual representation of the camera’s rotation and location in respect to the shapes of the boiler.


Matching the first camera angle with a primitive shape representing the boiler.

Matching an exact camera angle is a tougher prospect than you might think. Each camera basically has 7 relevant variables: X, Y and Z location, X, Y and Z rotation, and the lens angle.

X, Y, and Z locations describe the camera’s exact point-based location in the 3D space. Figuring out the general location is usually the first step to matching a camera. Often when figuring out location, I can use parallel lines in the scene to estimate a general range. For example, in the image above, the boiler is built of circular rows of bricks. By looking at which row is completely parallel with the image itself, I can tell that the camera is probably at a height which is level with that row of bricks. Then I can lock the camera to that specific height and move onto other variables.

Lens angle is the pin that holds it all together. This variable can make or break a camera angle. Basically, lens angle describes the exact section of perspective which is seen by a camera. When you zoom using a camera, lens angle gets very narrow, showing only a tiny piece of a point’s perspective. Zooming out, on the other hand, shows a wider lens angle, framing a much larger portion of the view. Needless to say, getting this value exactly right is imperative, as it directly affects the apparent scale of objects in the camera’s view. If you can manage to estimate the lens angle with accuracy, the rest of the matching is quite simple.

Ytram Cave wireframe

A wireframe pan of the balcony and Ytram cave areas' half-completed guideline meshes.

Once the first shot is lined up reliably, the rest of the process is simply branching out from that information. Then, more cameras are lined up with the basic model. These multiple camera angles then allow more models to be added in which match all of the current camera angles.

Sometimes, angles need to be adjusted to match new models, as well. For example, on Boiler Island, I had most of the boiler area set up and matching well. Then I moved ahead to matching the balcony and cliffs, and realized that none of my camera angles were matched accurately enough for extremely distant features to line up properly. This led to me going back and realigning every camera angle I had set so far, so as to match the new details of the cliff walkways and the balcony.

Ytram Cave walkway

The exit from the Ytram cave to the cliff walkway, matched with a wireframe of our recreation.

Of course, the process of camera matching is only a precursor to the final environment. During the course of matching camera angles with the geometry on the scene, I try to use as little detail as possible to convey the basic lengths and angles necessary to match each new camera angle. I do this both to keep the scene uncluttered, as I do much of my matching work in a wireframe view, but also because what I’m building will not be used in the final game, so dwelling on its details would be a waste of time. The models I create during the camera matching stage are simply to be used as guides when creating the final game assets. The camera matching stage is very freeform and branching, whereas the final modeling stage will likely be much more structured and organized, simply because of the detail involved.

Ytram Cave with the new geometry fading in and out

The newly made Ytram cave walkway is shown here, matched with an image from the original.

The stage of camera matching is certainly where we get our most concentrated exposure to the details of Riven’s original images, exposing some of the mistakes and odd anomalies that dot the images. For example, in an image standing by the boiler’s controls, looking up towards the pump system, you can see towards the lower left of the screen the handle of the paper press, an object that was intended to be completely removed from the game before it was released. (The image’s filename is “287_bislandcrater.1590.png”, for those interested enough to look for it.)

All of this work will culminate to a set of guideline meshes which will span the island and make the final asset creation that much more accurate and streamlined. Camera matching, while tedious and time consuming on its own, stands as an integral part of the process. It allows a level of loyalty and exacting similarity to the original not available by any other means.