X y and Z - why are they messed up?

In typical game design X and Z axes is left/right and forward/back with Y being up/down

but why is SL the ONLY ever program to use Z as the up/down axes and y as forward/back. Is this a typo made by Linden thats just fallen in place or is the entire "world space" built on a 90 degree angle?

That explains why i keep sliding off the grid

imogen

Just a thought but whereas a 3D modelling application might be orientated in no particular preference, SL has a map. On ground level, like graph paper, you start with X and Y. The addition of height into the formula introduces the third dimension, Z?

Yeah, my husband works in a 3d environment and that was his first complaint. Since I'm not as familiar, I adapted with ease to SL unusual building environment.

It's always annoyed me but it must be that our avatars are usually standing at a 90 degree angle ot the ground. If we are lying down Z aims through us, at the sky. With a normal 3D app, z is forward back, y up and down and x left-right.

SL uses the standard orientation for axes in solid geometry. I don't know if the 3D software underlying it has that orientation built in, but it certainly makes sense both for 3D graphics and for the physics engine.

A lot of software that began life as 2D already had X-Y used for the plane of the screen, and then wound up being forced to add a third dimension. HTML for web pages may be the most obvious example, but I believe windows systems going as far back as the original Xerox Alto used Z-order to refer to the relative positions of frames forward and back.

Don't worry about it, it really doesn't matter. In SL, objects will get local orientations totally skewed from the world coordinates. If you're doing LSL scripting, especially involving physics, things will stay stable in a way that makes sense, and you'll have harder problems to deal with than the axis orientation. If you're building, sooner or later you'll have to deal with skewed axes anyway, so you may as well get used to not being bothered by it.

SL is not messed up. It is arbitrary, and many, many different software and pencil/paper systems use different coordinates.

As for "other games", guess what? Second Life isn't a game

Are they still calling it a 3d chat client or something?

That is the great thing about SL. It can be whatever you want it to be.

I've grown up using design software with X and Y as the "ground" and Z being vertical. As far back as using AutoCAD 10 back in the 80's.
As far as I know it stems from milling machines used in machine shops. The X Y axis is the table that moves front/back and side/side and the head of the milling machine is the Z axis.
Autocad, mechanical desktop, Solidworks, Inventor...they all use that system.

Perhaps most games that you are thinking of use X and Z in their movements(joysticks?) because joysticks were originally designed for flying applications and forward /backward on a joystick is up down when flying?

In relation to the grid, you walk on the ground in X, Y coordinates. Z would have to be up.

Rather, if you look down at the grid from above your head, X is left-right, Y is up-down and Z is forward-backward.

SL is not backward. The problem is, you are not looking at the grid straight on, as if you were looking at a tv screen or a piece of paper.

just wondering.. is it really the ONLY program thats ever used this coordinates style?

This is correct. And as Markubis notes, AutoCAD and every other real-world surveying and modelling software I've ever encountered uses the Z axis as "up." Maybe part of the "games" is learning to think sideways

Take any advanced physics class. X and Y are the "horizontal" axes which would lay along the ground. Z is always vertical, aka the "normal" axis to the XY plane. SL has it exactly right.

No. Not by a long shot.

didnt think so =P

I've programmed in 3D, when through a whole bunch of help references. and SL is the only thing that puts the Z as up and down.

No, it isn't.

how many resources do you think I used or how far I would take it as a hobbiest programmer. I only went as far is it goes for client side programming. it makes sense for server side atleast.

I have no idea how much of anything you have looked at. I'm just saying that despite you and the OP's claims, Z and Y aren't different in every other program. I came to SL with experience using 3D packages, and some of them use SL's scheme. Truespace, for example.

To my knowledge most 3D environments render the ground plain in relation to the X and Y axis, and Z being elevation. As mentioned this may be different in flight simulators due to joystick layouts where Z becomes the left and right rudder control and Y becomes the up and down elevator input.

Even in Lightwave, a computer modeling and animation program I dabble in X and Y are ground plain axis, if I modeled along the X and Z axis the object would end up 90 degrees to the ground plain.

Here is a wiki article on Axis and Second life---that explains it. The reason the Op is questioning the Axis is because the SL axis is different from 3D modeling defaults. Maya and Softimage and other High end programs use the Cartesian right handed orientation--although you can change this if you want. So when you are experienced with these (like me) and come into SL ---the SL tools are very annoying. If you are coming from a CAD background then the Sl system seems correct. Lightwave was mentioned above...I havent used that in years--unless it has changed in recent times it too, uses the cartesian system. Left Handed system=Evil. Right handed system=Good.


"An axis is a component of a coordinate system. In SL the 3 axes are the x (red, forward/back, horizontal) axis, y (green,left/right, horizontal) axis, and z (blue, up/down, vertical) axis.

Note: in traditional, Cartesian-coordinate systems (basic algebra and geometry), the x-axis is left/right, the z-axis is forward/back, and the y-axis is vertical, not the z-axis, which can be quite confusing and frustrating. Why SL and some 3D modellers (3D Studio Max) have to be different, I don't know! Would be nice to have an option to switch the vertical axislike Maya does.

Difference of opinion. Most algebra is treated on a 2-dimensional plane first, with X and Y being the axes used for that. Z is used for depth. So most algebra and geometry is actually working from an 'overhead' view from my point of view when I learned the topics back in the 6th thru 8th US grades. Most games (Quake, Unreal, et all) work the same. X and Y form the default plane of movement, Z is treated as depth, because most level design is still done as a series of layers of 2D 'floors' like in real life buildings. 3D Studio Max is the most-used video-game modeller, ergo why it has the same idealogy.

The reason why SL uses this type of coordinate system is quite simple:
DirectX uses a right-handed coordinate system, where Y is vertical.
OpenGL uses a left-handed coordinate system, where Z is vertical.
Since SL (as well as Quake and Unreal) uses OpenGL, this is why SL uses that coordinate system.
The left handed system is mostly used by engineers, the right-handed system by mathematicians.
That's also the explanation, why 3D Studio Max uses that kind of coordinate system. It's not because it's widely used for creating video-game models, but you "engineer" objects. And any kind of CAD program uses the left-handed coordinate system"

A very informative post. Thanks Rebecca for making it.

I'm glad I searched it out. Since I have been in SL I never searched it--I just agonized over it.

3d Studio Max as well as Autocad and other CAD programs use the same orientation of axes as SL. Maya and other 3d apps which evolved from the SGI apps of long ago use Y as the vertical axis. It only seems odd in SL if you come from a background of using one of those apps. I've always thought using Y to represent the vertical axis is a bit bizarre, but the mindset it comes from is that the screen plane is X/Y and the simulated 3rd dimension moving back form the plane of the screen to the horizon is the depth axis. I guess that made an odd kind of sense when 3d graphics was new. It seems silly now.