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.

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

-- 

Regards
     Stephen

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