Talk:Homogeneous coordinates

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Mathematics rating:	Start Class	Mid Priority	Field: Geometry
Please update this rating as the article progresses, or if the rating is inaccurate. Click to show/hide comments. Please add to or update the comments to suggest improvements to the article. Close to B class: references needed. Geometry guy 20:55, 20 May 2007 (UTC)

About One Point Is Affine And The Other At Infinity: I think this is misleading. After all, by a projective transformation one can put both points in general position - which is the first case considered. In fact it is 'illegal' to speak about (0:0:0:0).

Charles Matthews 07:49, 14 Jul 2004 (UTC)

I believe the whole linear combinations paragraph is useless and inelegant. We already have the definition of scalar multiplication and addition - and exactly to avoid these problem, we do rescaling by multiplying for the last coordinate (w) of the other point - which avoids the = 0 special case. Additionally, the current text is probably incorrect when b = 0 - and this brings an interesting point up: which is the result of 0(1:1:1:0) ?

I do not see your point about applying the projective transformation - yes, we can apply the transformation, add the two points and transform them back, but there is no point in using that.

Paolo Giarrusso 18:01, 8 December 2005 (UTC)

The definition of addition for a pair of projected points doesn't look correct in the case that both of those points are in the plane at infinity.

[edit] left and right homogeneous coordinates

Homogeneous coordinates of quaternion vector spaces can be either left or right. That is one can specify that left multiplication by quaternions produces equivalent coordinates, or right multiplication does. Is left and right homogeneous coordinates, standard terminology to refer to both these situations? --MarSch 10:35, 19 October 2006 (UTC)