stupid question (what else is new) ...

while working on my 3D-Editor/Game Engine i came to realize that the default Rotation Matrix for OpenGL uses a counterclockwise winding for Rotations around the Y-Axis (Yaw), meaning if you look at a Object in the XZ Plane a Positive Angle will Rotate the Object Left, a Negative Angle will Rotate it Right.

This is Counter-Intuitive and i am wondering if there is a rule for this behavior in a Cartesian coordinate system or is this merely a "personal preference" for OpenGL ???

My editor currently uses the clockwise approach, where a positive angle rotates the object to the right instead, which seem much more intuitive.

searching the web, i have found both approaches, but i would like to know if there's a "corret" way to do it ...

Andy

polar coordiantes are mesured anti clockwise...

QUOTE (dinomium @ Dec 30 2004, 09:32 PM)

polar coordiantes are mesured anti clockwise...

alright, so this would be the correct matrix then:

cos(angle)	0	sin(angle)
0	1	0
-sin(angle)	0	cos(angle)

hmmmm, maybe i will just make it an option for the enduser ...
Andy

two quotes for you:
Chevy Chase as President Ford "It was my understanding there would be no math..."
or
Malibu Barbie "Math is Hard!"

either way that is just more trig than I care to remember... and not this close to new years!!

Shoot. I thought this was going to be one of those impossible to solve problems about two trains leaving at the same time travelling towards each other at different speeds.

Looks like A.f.d bait to me...

I was hoping this was some sort of game with a fake prize.

KT

That's some deep doo-doo Andy..... you flipping developers kill me.

Sounds like the rare matting call to attract Alfreds.

Almost like Jennette MacDonald and Nelson Eddy I'm calling yooooo hoooo


Sorry Andy I couldn't resist

QUOTE (swood @ Dec 30 2004, 11:14 PM)

Shoot.  I thought this was going to be one of those impossible to solve problems about two trains leaving at the same time travelling towards each other at different speeds.  :blink:

_YOU_ are the engineer on a train traveling from New York City to Chicago...

Yeah, Standard Polar coordinates are counter clockwise. And they were derived from Standard Carteasean coordinates.

Think of it this way: in an xy plot of a ray beginning at the origin, as the slope increases from zero to ninety degrees (and beyond) - the ray rotates in a counterclockwise direction.
Everything else follows from this example.

What some people solve with math others would solve with a hammer. Hit the coil until you loosen the wires. Then wind them the other way. This should achieve what your after without changing the math.

Maybe there's someone out there that could post some scanned articles from old Road and Track issues to explain this

QUOTE (rick 918-S @ Dec 31 2004, 06:24 AM)

What some people solve with math others would solve with a hammer. Hit the coil until you loosen the wires. Then wind them the other way. This should achieve what your after without changing the math.

Th best quote in a long, IMHO.

I teach a couple of graphics classes using OpenGL and somethings are not really sensible to us normal people?! Try this website as there are many really good tutorials and explanations: http://nehe.gamedev.net/

"It's a farging trick question!" - Roman Maronie

/ v <=> b:© + h(M)

/ angle
v dangle
<=> proportional to
b: beauty of
c cutie
h heat
m meat


.........einstein

.........b

My cat's breath smells like cat food.

As Homer said:

Y're all nuts. I'm goin' to Moe's.

QUOTE (Red-Beard @ Dec 31 2004, 05:12 AM)

Standard Polar coordinates are counter clockwise. And they were derived from Standard Carteasean coordinates.

that's what i wanted to know. the math is easy, just didn't know if there was a "right" way to do it.

counter-clockwise it is then ...

easy enough,
Andy

PS:

QUOTE

http://nehe.gamedev.net/

alreayd bookmarked for quite some time now ...

PPS:

QUOTE

My linear algebra is rustier than the "hell hole"

that's why i didn't ask you in first place, plus, you just can't seem to give an simple answer to a simple question ...

QUOTE (SirAndy @ Dec 31 2004, 11:54 AM)

PPS: QUOTE My linear algebra is rustier than the "hell hole" that's why i didn't ask you in first place, plus, you just can't seem to give an simple answer to a simple question ...

I still think it's easier to rewind the coil.

I had a diesel engine that would run backward.
I didn't even have a coil.

Pie=MCsquared

And if the pie is hair pie, it is cubed.

Paul

Sor Ahndie...

Is this code going to be used in the northern or the southern hemisphere?

Ya know you have to be counter clockwise in the northern hemisphere and clockwise in the southern hemisphere.

Magnetic fields reverse in the southern hemisphere, water spins in the opposite direction as it drains, monitors become unaligned, and a lot of the rules change down there.......

Bet you didn't know that......

Ken

QUOTE (kwales @ Dec 31 2004, 04:33 PM)

Is this code going to be used in the northern or the southern hemisphere?

it's going to be "universal".
which means, you'll have to float in space to be able to use it ...

Andy