View Full Version : y is up or z is up
02-25-2003, 12:48 PM
Offtopic, but always curious.
I have been having a discussion with a bunch of science types. Now conceptually I think of y as being up. So in 3d graphics, when you look at a scene you are looking down the z axis and y is up and x is right (or left).
Looking down the z is not the problem. The mathy-sciency types can see that. But they are used to using the z as up.
So, that got me (translate as some arrogant sciency-mathy type http://www.opengl.org/discussion_boards/ubb/smile.gif) thinking that maybe my way was "abnormal".
Thus.. what do you guys think!
Is y up or is z?
02-25-2003, 01:41 PM
It all depends on your perspective ( no pun it depended) , in the real world most users would look at Z being up, that's why most 3d Real-time simulation programs and higher level API's use Z as up and not Y.
I work a lot with API's like Vega, Performer and Vega Prime and they all present Z as up vector, but in the world of real-time simulation this can also get very complicated and compounded with the issue of having to use different coordinate systems like flat earth, round earth,Geodetic, Geocentric, UTM, Trapezoidal, Lambert, Longitude and latitude etc.
Personally I think with Z as up and when I have to drop down to Opengl I have to remember Y.
So in Opengl up is Y, but in the way up is generally presented to the end user Z is up ( in my experience http://www.opengl.org/discussion_boards/ubb/wink.gif )
[This message has been edited by UrbanLedgend (edited 02-27-2003).]
02-25-2003, 03:49 PM
Yea depends on how you look at it.
I am a engineer and Y has always been up to me.
In most physics book use Y as up, X as distance.
I got my feet wet with 3D programming with POVray which used Y as up.
Then of course OpenGL
02-26-2003, 02:20 PM
I remember a professor of mine that had an interesting idea about this.
In CG(OpenGL at least) z comes out from the screen and in CAD z goes up. He gave the following explaination.
When an architect sits down at his desk to draw some blueprint, x and y goes along the table and it is then natural to put z up.
Someone involved in computer graphics sits down at their desk looking at a computer screen, which has x and y along the screen sides. Here z goes out.
02-27-2003, 03:33 PM
Or similarly architectural plans in 2d on paper have x, y!
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