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From Luc Maisonobe <Luc.Maison...@free.fr>
Subject Re: [math] Cross and Dot Product (not centered at the origin)
Date Fri, 17 Jun 2011 06:59:38 GMT
Le 16/06/2011 21:43, Curtis Jensen a écrit :
> On Wed, Jun 15, 2011 at 12:01 PM, Luc Maisonobe<Luc.Maisonobe@free.fr>  wrote:
>> Le 15/06/2011 19:57, Curtis Jensen a écrit :
>>>
>>> The Vector2D and Vector3D classes have dotProduct and crossProduct
>>> methods.  I assume this is done be considering each vector originating
>>
>> There is no crossProduct in Vector2D in the current version I think.
>>
>
> You are correct.  It was sloppy typing on my part to include
> crossProduct with Vector2D.
>
>>> from the origin.  How can the dot product and cross products be
>>> calculated for vectors not centered at the origin?
>>
>> Yes, these methods are intended for vectorial spaces, not affine spaces,
>> which implies they work for vector centered at origin.
>>
>> We discussed on the dev list about having separate classes for
>> Affine/Vectorial spaces and finally decided to merge everything in only one
>> class per dimension. This is a classical choice and the user often already
>> know what his instances represent.
>>
>
> What is the suggested way of getting the dot and cross products for
> vectors not centered at the origin?  ie. the dot product of a corner
> of a polygon.

Something along these lines:

    Vector3D edge12 = vertex2.subtract(vertex1);
    Vector3D egge23 = vertex3.subtract(vertex2);
    double dot = edge12.dotProduct(edge23);

Luc

>
> Thanks,
> Curtis
>
>> Luc
>>
>>>
>>> Thanks,
>>> Curtis
>>>
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