Orientation start point...

hello there,
I hope I’ll be able to express my self correctly, under OpenGL when I say my heading is 85 degrees for example, 85 degrees from what??? and how do I change it???
we have a visualizing API and a Physix API and there heading is allways -90…
so how do I change the Heading start point for one of the aPI???
thank you…

Absolutely no idea what are you talking about.

I think he has some sort of rendering and physics engine where they have ‘heading’ of objects which is always -90. That is, models are always aiming to the negative X-axis (heading is the rotation around Y-axis I think). He is asking that, if he rotates something 85 degrees, what is the 0 degree angle, and how does he change this origin using OpenGL… This is my theory.

HenriH thats my question exactly!!!

and??? any idea??

Perhaps it would be a good idea to ask your question on a forum where they have knowledge about the Physix API?

Ok, I didn’t want to write anything as I have really no experience on the topic, but: if you need to rotate you objects, you can just rotate them; but in OpenGL there is no such thing as “heading”. Wheather an object aims a particular direction only depends on the way that object is modelled. So, to be precise, your question is just not correct.

well I’m using the same object in two different OpenGL based API. On the first API (VegaPrime) heading 0 is pointing to the left, on the second API heading 0 is pointing to the right… that’s the fact what is wrong about the question I didn’t get it

In OpenGL there is no such thing as “heading”. Rather, objects are precisely like you define them. If you want an object to point in another direction, you have to rotate it in OpenGL or change it’s vertex coordinates accordingly. I have no idea what VegaPrime is or what do you mean by “OpenGL based”, but it is apparently not OpenGL. I would recommend you to seek advice at the corresponding forums for the APIs you are using.

Maybe they use different coordinate system in this VegaPrime thing. OpenGL uses right handed coordinate system; X is aiming to right, Y is up and Z is aiming towards you, outside of the monitor screen. Rotations are always counter-clockwise rotations along some axis.

You can visualize this by sticking your thump of your right hand up (along the positive Y-axis) and closing your other fingers. Now your other fingers should lead from right to left, which is the Y-axis rotation. This is the right handed coordinate system the standard OpenGL uses. If you stick your thump right (the positive X-axis) now your other fingers lead from down to up. This is the X-axis rotation etc…

Don’t know for sure, but VegaPrime probably uses the SGI Performer coordinate system by default: right handed coordinate system where you’re looking down +Y, +Z is up, and +X is to your right. For aviation hysterical reasons, heading is a clockwise rotation about Z (0 deg = looking down +Y, 90 deg = looking down +X, etc.), which means you negate heading to get the mathematical rotation.