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Handling perspective correction

From: SketchUp Rendering Using V-Ray

Video: Handling perspective correction

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.

Handling perspective correction

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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SketchUp Rendering Using V-Ray

33 video lessons · 5830 viewers

Brian Bradley
Author

 
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  1. 4m 30s
    1. Welcome
      1m 14s
    2. What you should know before watching this course
      2m 33s
    3. Using the exercise files
      43s
  2. 7m 52s
    1. Installing V-Ray
      2m 27s
    2. Locating V-Ray tools and features
      5m 25s
  3. 39m 2s
    1. Creating natural daylight with the V-Ray Sun and Sky
      7m 41s
    2. Using the Omni Light
      7m 9s
    3. Exploring the Rectangle Light
      6m 2s
    4. Exploring the Spotlight
      4m 37s
    5. Exploring the IES light type
      5m 0s
    6. Setting up image-based lighting
      8m 33s
  4. 29m 40s
    1. Working with irradiance mapping
      12m 8s
    2. Creating a light cache solution
      6m 14s
    3. Using the DMC engine
      11m 18s
  5. 23m 11s
    1. Overview of the physical cameras
      5m 16s
    2. Understanding the Exposure controls
      6m 23s
    3. Handling perspective correction
      3m 4s
    4. Setting up for a depth-of-field effect
      8m 28s
  6. 44m 59s
    1. Introduction to V-Ray-specific materials
      9m 41s
    2. Creating diffuse surfaces
      9m 44s
    3. Creating reflective surfaces
      8m 2s
    4. Creating refractive surfaces
      9m 53s
    5. Creating translucent surfaces
      7m 39s
  7. 44m 8s
    1. Using fixed-rate sampling
      10m 21s
    2. Working with the Adaptive DMC engine
      11m 48s
    3. Controlling the Adaptive Subdivision sampler
      10m 15s
    4. Exploring subdivs and the DMC Sampler controls
      5m 52s
    5. Manipulating color mapping
      5m 52s
  8. 33m 39s
    1. Adding displacement to materials
      10m 48s
    2. Using caustic lighting effects
      7m 37s
    3. Creating occlusion effects
      8m 13s
    4. Creating a non-photorealistic render (NPR) with the Toon material
      7m 1s
  9. 1m 21s
    1. What's next?
      1m 21s

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