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Oftentimes, when producing visualization renders, a SketchUp artist maybe asked to mimic the use of a perspective control or shift lens as employed by many visualization photographers. These lenses can actually be moved parallel to a camera sensor. The basic idea being that they give a photography ability to control the appearance of perspective in an image. Architectural photographers often use this functionality to avoid convergence of the vertical lines in tall buildings, but of course the functionality can be used to straighten the verticals in any perspective photograph.
If we take a render of our perspective start scene, we may see why this piece of functionality, the ability to straighten verticals, could be a desirable to for our rendering process. Straightaway we can see that we have a number of lines in our rendered image that are leaning quite badly. This perhaps may not be what our client expects. They want to make certain that all of the verticals in their architecture really do look vertical. Now you may be thinking well, that isn't a problem, because SketchUp has perspective correction tools of its own.
Well, that it true; the problem is V-Ray does not work with them. At render time we would still have an image identical to that scene in the V-Ray Frame Buffer this moment in time. The good news is that V-Ray does give us a tool of its own with which we can work. To access it, we need to come up to our Options Editor, or Options dialog, and into the Camera rollout. The control we want to work with is down in the CameraPhysical group. It is this Lens Shift option that we did say we would be coming back to.
Now as you would expect from a single parameter, this tool works in a very simple way. Positive numbers cause our vertical lines to diverge. This makes objects appear to lean towards the camera. Negative values will force them to converse, or appear to lean away from the camera, which is the problem see in our current render. Now, for your scene, where we are using a 30 mm lens setting, a Shift value of about 0.23 ought to be sufficient to make our lines appear to stand vertical. With that change, we can dismiss our Options dialog.
Now if you're not certain which lens settings you are working with, or rendering with, inside SketchUp at this moment in time, if you just come across to the SketchUp Zoom tool, left- mouse-click on that, you'll see over here, in the bottom right- hand corner of the interface, we get a readout in millimeters of our current focal length. Now of course, we need to take another render to see if that has corrected our problem, which of course, it clearly has. It has been said, oftentimes the simplest tools save us the most time.
Now we could've performed these perspective corrections in an image editing application such as Photoshop, but as we have such an easy-to-use and readily accessible control on our V-Ray Physical Camera it makes sense to use it. It makes for easy perspective correction, taken care of right here at render time.
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