On Sunday 26 August 2007 00:51, Joel E. Denny wrote: > Third, there are cases where the interpretation of "left" alone is > unambiguous and it should be interpreted as a corner, but it's a > syntax error instead. My original example in this thread is such a > case: > > .PS > A: circle "A" > B: A left > circle "B" at B > .PE > > I see no ambiguity because I don't see how it makes sense to > reference an existing object with a direction modifier. That is, > even if A referenced a line, its direction was chosen when it was > drawn. Thus, it's clear to me that "B: A left" means set the label B > to the left corner of A.
Even if this were true, it makes no sense in geometric terms, to refer to the `left corner' of an object. What, exactly, should that be interpreted to mean? In your example, object `A' is a circle; it doesn't have *any* corners! The only possible interpretation of `left', as a location rather than as a direction, is the x-ordinate of the tangent line touching the leftmost point on the circumference of `A', and that refers to an infinite set of locations, (although your intention is presumably to refer to the unique point at which this tangent touches the circle; in traditional pic, this would be referred to as `A.w'). Even if `A' represented a box, unless it is drawn inclined to the co-ordinate axes, it has no `left corner'. The only situation in which `left corner' has any geometric meaning, is when the object is a polygon, of three or more sides, with exactly *one* vertex positioned further to the left, in the X-Y co-ordinate plane, than any other vertex. In the general case, this usage is geometrically ambiguous, and IMO, it is best avoided. Even in the gpic case, where `A.left' is accepted as an alternative to `A.w', this means `the centre point of the left side of object A', so it does not represent a `corner', and to refer to it as such is nothing but confusing; additionally, as Ted has already stated, the correct syntax is `A.left', or `at left of A', (strictly, this should probably be `at .left of A'), but not `A left'. Your example can be written, much more intelligibly, as .PS A: circle "A" B: circle "B" at A.left .PE or as .PS A: circle "A" B: circle "B" at left of A .PE Why do we need to accept the more confusing form of expression? Regards, Keith.
