Method for perspective matching

[Bill Gilliss]

I hate to say it, but I have never really been successful with using Walkabout to accurately match the perspective of a view of a model to the perspective of a site photo. Sorry, Ray, but it's mostly a matter of the controls -- I find AutoCAD's Full Navigation Wheel to be far more capable, intuitive, and responsive. So here is what I do in modelspace, and it works very well.

1. Determine the proportions of the site photo image. If it is 4000x3000 pixels, it's proportions are 1.333 to 1.000.
2. Adjust the proportions of a maximized modelspace window until it has these same proportions. I adjust the width of the docked Properties and nXt palettes to do this, one on either side of the screen. I measure with a ruler right on the screen. Hi-tech, huh?
3. Create a perspective view more or less corresponding to the camera location and target. Save the view with a nice short name you won't mind typing often.
4. Use View manager to apply a background to this view, using the site photo as the background, stretched to fit. Since the proportions of the window match those of the photo, the photo will not be distorted.
5. Enable the navigation wheel with Shift-W. This enables the properties of the view, where you can set focal length, camera and target height, etc.
6. From there, use the navigation wheel's Orbit, Look, Pan, Walk, etc., as needed to get things to line up. I do not use the mouse wheel. Save the view each time you make an improvement. I usually use the X-ray visual style so I have a sense of mass in addition to being able to see key points on the underlying image.
7. When I do a final render, I usually use the same pixel size as the site photo (4000x3000). The various pieces align easily in Photoshop for post-rendering composition. I rarely use the background image as the nXt rendering background because the image quality gets degraded.

(Note that I do not use a paperspace viewport to do all this. I have found that the site photo background does not have the predictable proportions it has in modelspace. Don't know why.)

I find this method to be smooth, fast, full-screen, and free. Barring a real mathematical tool to calculate horizon lines and vanishing points, it works for me. I'd appreciate any suggestions you might have.

[Miguel Tano Adanes]

I totally agree with you, Bill. As an architect who have to do with building restoration, mostly, camera match is THE tool I really need to say nXt perfectly suite to me! I tried to load the model into SketchUp, make a camera match (in SketchUp is very simple and gets good results), save the view, export the model into ACAD, but the views don't correspond (don't know why!!), and nXt doesn't read views different from cameras (other issue to be solved, in my opinion).

[Marc Chaumier]

I agree, the walkabout window is not the best tool of nXt. But you can improve the manipulation. You have to take the picture of the background you want to use, and reduce the resolution to 700x500 or something so, in the same proportion as the initial BG. Then, you use this very light image as background in the walkabout window. You can move the "increment" cursor to adjust the speed of the mouse.

You can choose any resolution you want with this slimmed-down background, for the final rendered file... And render it in tif with alpha channel, to put the real background in pshop or other.

One last advice, if the perspective doesn't match exactly to the background, no problem! In pshop, you modify your background for it match your render. And keep it so, so you can do other trials.

Xcuse my bad english!