The undistort function for equirectangular images assumes width = 2*height which is not always correct

In some equirectangular images, the width is not equal to 2x the height. In these cases, the denormalized_image_coordinates is incorrect, since the normalized coordinates will range from -0.25 to 0.25 (height) and -0.5 to 0.5 (width). This can cause the function to crash or to produce poor multiview stereo results. The fix is simple. For equirectangular images, modify denormalized_image_coordinates to multiply normalized value by width (for x value) and 2*height (for y value). This impacts only the rendering to perspective images.

Separately, the SfM can be improved for 360 images by undistorting, computing features on undistorted images, and projecting feature coordinates back to the 360 images, rather than computing features on the equirectangular images.

Locate the undistort function and its denormalized_image_coordinates calculation, then inspect the rendering-to-perspective path. Reproduce the behavior with an equirectangular image whose width is not twice its height and verify that x uses the width while y uses twice the height, without regressing standard dimensions.