On 11-4-2016 1:09, Stephen wrote:
> On 4/10/2016 3:37 PM, clipka wrote:
>> Am 10.04.2016 um 15:00 schrieb Stephen:
>>> On 4/10/2016 1:37 PM, Bald Eagle wrote:
>>>> The coordinate system is a static "thing"  It doesn't "do" anything.
>>>> Look_at just determines what direction the camera is pointing when
>>>> it's at a
>>>> given location ("vector").
>>>
>>> Just one thing to mention. There are two coordinate systems*, Y up and Z
>>> up. Depends if you are a mathematician or an engineer. Moray used Z up.
>>> There is also left hand and right hand versions too.
>>> One of the reasons I use a modeller I cannot visualise scenes well
>>> enough to be a true Pover.
>>>
>>> * Not counting all the fancy ones like Polar, Plücker, cylindrical etc.
>>
>> In other words, you refer to cartesian coordinates only.
>>
>> Well, actually there are only _two_ fundamentally different
>> 3-dimensional cartesian coordinate systems: A right-handed one and a
>> left-handed, and _infinitely_ many different orientations of those two
>> coordinate systems, each of which are equally valid from a mathematical
>> point of view.
>>
>> So accomodating only for the handedness and a choice of whether Y or Z
>> is up doesn't quite cut it.
>>
>
> Well it confused me going from Moray's Y up to PovRay's Z up coordinate
> system. It is easy to make a mistake. It was also the source of many a
> flame war, years ago.
> A 2D X-Y plane is looked down on like a piece of paper by mathematicians
> and Z is up/height. Whilst Engineers looked into an oscilloscope and Z
> is depth. Or the other way around. Lutz of Moray fame wouldn't hear talk
> about it.
> It is a simple transformation to convert and I know for a fact Thomas
> has memorised it.

It's a mantra.

>
> So what doesn't cut what?
> I don't understand.
>


-- 
Thomas

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