+Z direction should be outwards from the visible tag surface

[ayberkozgur]

Currently, the +Z direction of the tag transform is towards the inside of the visible tag surface since the top left corner is the first corner and is the origin of the tag. For a virtual reality application, this creates a very awkward 3D model building process where the model is on the positive side of the X and Y axes but is on the negative side of the Z axis and is upside down. When exporting models (e.g to FBX), this also creates confusion concerning the positive axis directions. If the first corner is the bottom left one, the +Z axis will naturally point outwards when +X and +Y axes point towards the inside of the tag.

[severin-lemaignan]

I'm perfectly fine with using this convention (previous one look like a bug to me), but we probably need first to fix #19, I guess...

[qbonnard]

The rotation directions always seemed counter-intuitive to me, but I never took the time to check what was the best convention. Is there really a dominant convention, or is it another fight between people who think that Z should go up and those who think that Z should go down ? Compare with mathematicians who think that Y goes up, and graphic programmers who think that Y goes down. I really have no idea about Z, whatever makes users happy makes me happy.

Speaking of users, wouldn't such a change requite a major version bump, I.e. chilitags 3.x.x, in order to not silently "FLIP ALL THE THINGS !" ?

[ayberkozgur]

A major one seems like too much to me, I don't know... Maybe a minor bump, like 2.1 ? But there should definitely be a bump.

In terms of Z pointing up, I can definitely say that it would make my life much easier, since all landmarks will be parallel to the ground (like trees, rocks etc.) and their Z axes will point upwards. This will ease the modeling process greatly.