   finding surfaces (planes, curves) in images
  hello,quite sometime ago i came across a website from a guy that was analysing images and he was able to find the planes or even curve surfaces in that image where then he could project things with perspective.i would like to know if anyone know what is this technique and where could i get more info about it.look at this image. how could i find the curve surface of the image and be able to then project anything in it so that it would fit in the image?http://www.tonychor.com/archive/Stairs%201.jpg( i remember that it mention something about tracing lines across the image, finding edges maybe and after some times it would define planes or surfaces presented in the image )thanks in advance[Edited by - murderv on May 25, 2009 3:43:11 PM]
  In that particular image, there's a wealth of distinct edges, but very little useful shape information unless you assume that brighter surfaces lie in the XY plane, or something like that.If you can assume certain things about your scenes, there's a lot you can do. Otherwise you need at the very least some depth information, or a way to construct it (known- or guessed-distance separation of two images). Otherwise you're just constructing surfaces or locii in 2D space; basically, tracing.   ;  i remember the website i saw time ago he used greyscale images of buildings, and he could find surfaces in the images, even curved surfaces and he projected text sentences in it.the curved surfaces would go from one side of the building to the other and it looked pretty decent to me.if im not mistaken in the explanation he used an image of a plane in the sky and the lines were traced along the wings, etc and he could find different surfaces and shapes in a image and then project on it taking perspective and depth into account or atleast it really looked like it..wish i could find that site again rrr.i don't even know what keywords to use to search for something like this, i just know it exists, and i will look into what you said. even 2D space might do the trick, without the need for stereo images, , i guess, but thanks for your answer.if you have anything u think could be useful for my search please let me know.thank you.   