Topic: turntable transformation

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Jan_Bruijns (Over 1 year ago)
I like a option to tell synth that the photo's are taken with an object on a turntable with the camera mounted on a tripod. In this case the relative orientation of two succeeding camera positions an the relative translation of three camera positions (the ratio between the translation from position 2 to position 3 and the translation from position 1 to position 2 can be computed) gives the possibility to fit all camera positions on a circle with unknown radius (radius unknown is not important; the distribution of the camera position on the circle looking to the center of the circle is important). Then a reconstruction can be made with the double curved arrows for rotational navigation.
Nathanael (Over 1 year ago)
Hello, Jan, 

(For anyone else following along, here is the link to Jan's synth which inspired this suggestion: Model car BMW M3 )

The main problem with your photos of your car is that the background behind the car (the stucco-like wall) has a dominant visual texture and it stays stationary within the camera's field of view while the car moves. 

You can think of it this way: Photosynth's primary objective is to find all of the parts of the images you give it which are the same in all the images and to calculate the relative distance between them. In the case of your photos of your car, it correctly identified many of the same points in the wall behind the car and tracked them between all of the images, however because the wall had the same relationship to your camera through all of your photos, no orbital camera path was calculated.
Nathanael (Over 1 year ago)
I've seen many people go through this same expectation and disappointment, however shooting synths with a turntable is possible and instructions for how to do it for Photosynth are present in the Photosynth Photography Guide (available here in several languages: ). Turn to page 5 in the guide for turntable instructions. 

The main gist is that if you use a traditional turntable or lazy susan, the background (which is to say anything other than the part of the photo which is not turning) ought to be blank in order to allow Photosynth to track only the rotating object. This should activate Photosynth's 'object' mode and the navigational halo, although I must warn you that you have chosen a difficult subject with a shiny car, as reflections in shiny surfaces move independently of the other surface details.
Nathanael (Over 1 year ago)
Personally, I would recommend moving the camera around the car, over rotating the car in front of the camera. This way, you don't need to worry at all about blank backgrounds or anything else. When you move the camera around the car, the background and the ground underneath the car will all move correctly in relationship to the car and will only help Photosynth calculate the camera positions. 

In other words, Photosynth's prime directive is to determine the relative distances between all of the feature points in the images which it believes are the same in multiple images. When all objects that you care about seeing a point cloud of are stationary (i.e. a stationary car in a stationary room), you will get a point cloud of a car in a point cloud of a room and where the car's shiny surface makes for fewer image features, the rest of the stationary environment will help Photosynth keep its bearings.
Nathanael (Over 1 year ago)
If you really love the turntable, people have created their own 'inverse turntable', if you will, where an arm is constructed to mount the camera on which rotates around the stationary pedestal. Using a setup like this, you can easily shoot in a controlled manner while keeping the background moving in correct relationship to the subject, again negating the need for a perfectly blank backdrop.


I hope that my reply (I am only your fellow Photosynther) does not smack of simply defending Photosynth's current mode of operation and discounting your suggestion. I have tried to only explain what Photosynth is up to and how you can get what you want within those limits. 

I, too, have made similar requests (see: ), however the most expedient way to a successful synth is to just learn what it expects and conform one's own shooting to fit within that.
Jan_Bruijns (Over 1 year ago)
Hello, Nathanael. I know about the problem of textured background behind a turntable for synth. In such a case you get two sets of features. Zang, first working with Olivier Faugeras, now working at Microsoft, has published a paper in which he explains how to distinguish these two sets. So, it may be a major effort for the developers of synth but i think it should be possible to seperate the feature set of the background from the feature set of the object on the turntable. In the mean time i will try to create a new set the way you suggested.