Re: LANG: VRML Transforms (fwd)

Michael Pichler ([email protected])
Fri, 6 Oct 1995 15:01:32 +0100


>>>>> "C" == Colin Dooley <[email protected]> writes:
>> My viewer moves the object and then rotates it about the Y axis. VRweb
>> apparently rotates the object and then translates it. I hope this is clear.

C> The only way to do multiple transformations which makes any sense is:
C> 1) Scale
C> 2) Rotate
C> 3) Translate
C> Anything else will probably cause confusion at some point.

The order in which transformations appear in the VRML file must be
respected.

To stay with the example by Patrick Sweeney <[email protected]>:

Translation { translation ... }
Rotation { rotation ... }
SomeObject

When you think of local coordinate systems (what modellers usually
do), you first translate SomeObject to its place and rotate it then
locally on that place.

To achieve this effect in mathematical terms you must reverse
transformations. I.e. you have first to rotate SomeObject at the
origin and then tranlate it to its position. If you did the
Translation first you would rotate the object along a circle around
the origin going through that object.

In my eyes, this is no special Inventor issue, just basics of Computer
Graphics Transformations.

bye,
Michael


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