Is it possible / practical to stitch a panorama from 4 photos take from different positions (edges of a car's roof)?
I would choose the edges of the roof instead of a single position, to avoid needing to put the camera mounted in a great height on top of the roof.
Theoretically, it is possible.
However, practically it will be a laborious task while stitching and positioning the cameras to get non-overlapping images and not missing any details that may create problems while stitching.
In case the cameras don't have a desirable viewing angle then there are chances that the camera can't capture the image from the ground to sky. You will need one more camera on top of the car to minimise this issue.
Anyways check this link you will get more details.
https://photography.tutsplus.com/tutorials/create-a-photo-sphere-with-your-dslr-camera--cms-24939
@Mods, I'm not sure if external links are allowed. Sorry for that.
The main issue you'll have, if the cameras are separated by any distance, is parallax causing misalignment when stitching, particularly with nearby objects. There's also the fact that to cover a 360x180 spherical view reliably with enough overlap for stitching, you'd need a lens with a lot of scene coverage and even most rectangular 8mm fisheye lenses for APS-C aren't that wide (they're only 180º coverage diagonally across the frame, not along the edge). I've only ever been able to cover a sphere in four shots handheld with a full-frame circular fisheye. Theoretically, you can do it with two such lenses back to back, but that assumes you don't need any overlap for stitching or ghost/clone erasure.
It might actually be more practical to use a 360º camera (e.g., Ricoh Theta) mounted on the roof of the car, vs. four separate cameras and stitching, despite the lower resolution results.
Slightly offtopic, but could be useful for someone else looking for multiple cameras + panorama solutions.
Normally we don't like parallax and we prefer to capture the whole view from a single point to avoid stitching problems.
But sometimes it is desired. Parallax of multiple cameras can be used for reconstructing depth information and producing 360 stereo panorama for VR viewing. This has been standardized as "Omnidirectional Stereo" (ODS).
"Rendering Omni-directional Stereo Content" from google developers website:
Omnidirectional stereo (ODS) is a projection model for stereo 360 degree videos. It’s designed for VR viewing with a headmounted display (HMD). ODS uses a special projection format which has the following advantages:
- It is panoramic and stereo everywhere—there are no bad seams or dead zones (except directly above and below the camera, which we will discuss later). [...]
