We can use Hugin to create an equirectangular image from a six-image cube. For ease of keeping track of things, it is recommended that you name the files back, front, left, right, down, and up.
First, start Hugin and after it starts go to the Interface menu and select Expert from there.
Next, load all six images into Hugin via the "Photos" tab by clicking the "Add Images" button. When you are asked for information about the image, the field of view of the lens should be entered as 90° and the lens type as normal (rectilinear). If required, the focal length should be entered as 15.297 and the focal length multiplier as 1x.
Next, you'll need to set the yaw, pitch, and roll for each of the six images. You can do this by double-clicking each file name in the file list in turn. The roll value for all six is 0. The yaw and pitch values are as follows:
yaw pitch back 180 0 front 0 0 left -90 0 right 90 0 down 0 -90 up 0 90
After setting those values, you can preview the equirectangular image by clicking on the icon. You can then switch back to the main interface to generate the final TIF file.
Go to the Sticher tab and do each of the following:
The allows us to take a six-image cube map such as: