X-axis is inverted in output images

[allegroLeiden]

Output images are flipped left-to-right. This was brought to our attention by @dquenard.

[allegroLeiden]

We also figured out why. 😀 To understand it, consider the various coordinate axes. With theta=phi=0, the coordinate axes of the model look to the observer as follows:

        Y
        ^
        |
        |
X <-----O

with the Z axis pointing into the page. But the 'pixel' coordinate axes are arranged as follows:

Y
^
|
|
 -----> X