Does anyone know of a way (possibly: an easy way!) to obtain 30-degree-isometric pictures (tilted like in old computer games like SimCity) starting from a normal photo?
I don't know if all the necessary information is captured in a single image, but it would be an awesome effect!
While post-processing "normal" photos into isometric ones is quite complicated (as already described by other answers), you might have better luck with making (almost) isometric photos straight from camera.
Your images will be very close to isometric when the distance between your camera and closest object is orders of magnitude bigger than dimensions of subjects and distance-from-camera differences between your subjects. Satellite images are a well-known example.
Without any extra equipment, you could cover some small scenes, e.g. some smaller Lego creations. A high building, hot air balloon or (RC) aircraft would provide more height for appropriately capturing bigger scenes.
I could be wrong, but I'm going to go with "not possible."
What you need to do to pull this off is make all the objects in a frame the same scale, which is not how the camera captures it. So you would need to selectively enlarge or shrink objects based on their distance from the camera. And the degree of scaling would depend on the distance from the camera and that information is not recorded in the image (you can only solve for the distance of the focus point based on the focal length of the lens and the position of the focus ring).
You would need a lot of rulers/yardsticks/etc in the image to get the correct measurements or you could measure the items and jot them down in a book. While you're at it (if the image allows for it) you might want to shoot all the subjects separately so that you can get all the subjects in focus (if that's what you want) and so you can manipulate them individually before layering them on top of each other.
I'd love for someone to prove me wrong, but I don't think it can be done with today's cameras.
Edit: if you're starting with a normal photo you could estimate the sizes of things and selectively stretch in photoshop, but that'd take a lot of work and I don't think you'll end up with a good result. I think the biggest challenge with this is the ground as it all needs to be stretched at varying rates as you move away from the camera.
One key property of isometric images is that the scale doesn't vary with distance, i.e. all objects are rendered the same size regardless of distance from the camera. You can capture such images using an object-space telecentric lens. Such lenses are expensive, designed for small sensor machine vision cameras and most importantly, severely limited with respect to subject distance and magnification.
Long focal length telephotos can get close to approximating telectricity, probably close enough that the slight foreshortening will go unnoticed. Getting a 30 degree isometric view is just a case of pointing the camera at the correct angle to object.
I am not quite sure what you mean in your question, but I would like to introduce you to an interesting effect called tilt-shift photography - The interesting angle allows for extra information from various angles to be captured in the photo rather than a standard photograph, this makes a very interesting view perspective.
See http://www.smashingmagazine.com/2008/11/16/beautiful-examples-of-tilt-shift-photography/ for examples - sorry if this is not what you're after.
I don't think that it would be possible to do from a single exposure. Creating an isometric image would mean changing the perspective, effectively having to reveal objects that have not been captured during the exposure.
If you have multiple exposures from varying angles (vastly different angles, including aerial photographs), then you could build a computer model of the scenery, and then render the model from any angle.
Don't ask me what software can build the computer model. I know that some exists, but I don't know how advanced they are, and how complex models they can deal with.
