Visualizing Cubemap Image Rotation
It is not always easy to see how to lay out the images of a Cubemap when it is first being created. This method can help you see how to properly lay out the images for use with the NVIDIA Texture Tools plug-in for Photoshop.
Probably the easiest way to visualize the rotation of images for a Cubemap is to imagine yourself lying in the ground staring up with your body aligned to the Cartesian axes. This means you would be looking in the positive Z-Axis direction (up), with the X-Axis pointing to your right, and the Y-Axis pointing upward from the top of your head, like this:
But to see how this orientation plays into the layout of a Cubemap, let us consider these six images that represent a view in six directions.
Currently, all of these images are rotated straight up and down. Some will need to be rotated in order to line up properly. So let us go back to the example where we can imagine ourselves lying down as above.
Now, imagine turning your head to your right. This would mean you would be looking down the X-Axis. However, because you are still lying on your back, the view would appear rotated 90 degrees counterclockwise relative to your head, like so:
If you then rotated your head back to the left, you would see this for X-Axis negative:
To look at the positive Y-Axis image, you would have to rotate your head back. This would cause the view to appear upside-down, like so:
To see the negative Y-Axis image, you could look downward toward your feet, and you would see this:
The positive Z-Axis image is fairly easy to visualize, since you were staring up at it when we started:
To view the negative Z-Axis image, you would have to roll yourself over onto your stomach and stare straight down at the floor, so you would see this:
Once you had all of those images created and rotated accordingly, you then need to line them up in a single file in the following order:
X+, X-, Y+, Y-, Z+, Z-
When this has been completed, you will now have an image that should look something like this: