I have taken a number of pictures to create a 360-degree panorama. I add them to the Photomerge dialog in the order I want them to be stitched, but Photoshop insists on stitching them together in another order, starting with one of the images in the middle, so that the object I want to be centered in the panorama gets placed out to one side.
What am I doing wrong? How do I get Photoshop to start with the image I placed first in the list of files?
Assuming you shot images out of order, the files in the list have to be in the order you want them to be stitched, so renaming the files, or adding them in order, (i.e., add all the images to the left, then your central one, then all the images to the right) are probably your only options.
You could also use a fuller-featured stitcher, such as Hugin (open source), which will allow you to reorder the images, as well as define the actual control points used, where the same features show on a pair of the member images.
If, however, there are not enough distinguishing characteristics for a stitcher to find and match (e.g., horizons and blue sky and nothing else), you may have issues trying to use a simpler stitcher like Photomerge or Microsoft ICE, that doesn't do manual definition of control points.
Photoshop tries to detect the correct order and reorder them for you, based on the edges lining up. So to answer the why side, PS is probably confused based on the photographs' content about what order they go in. Several answers suggest using a different stitcher that allows you to specify the correct order manually, likely the best option.
