On Sep 22, 2010, at 10:41 AM, David Singer <singer@apple.com> wrote:
> On Sep 22, 2010, at 8:02 , Brad Kemper wrote:
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>> That may be ingrained into your understanding of rotation, but I do not think it is a common way to think of angles as specifiers of linear direction. If someone asks me to draw a 45 degree angle, I draw a line pointing to the right and another line, connected to the first on the left, pointing up and to the right. If superimposed on a square it would go from lower left to upper right corners. When I draw that angle, it never enters my mind which direction the positive y-axis points, and I have no expectation that it matters. I really don't think I am unusual in thinking this way, except perhaps amongst a this crowd.
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> OK, but that's not quite what the question is. "Draw a line at 45 degrees" is more like it, and is likely to result in one of 3 responses:
> a) 45 degrees to what?
> b) given a piece of paper, a line from top left to bottom right
> c) given a piece of paper, a line from bottom left to top right
The reason for asking for an angle to be drawn instead of a line, is that it does provide a reference line that way (the zero degree line), and you don't have to ask "45 degrees to what?". If you then point to the angled, non-horizontal part, and say "what angle is that line?", the answer will be "45 degrees", not "minus 45 degrees" or "315 degrees". Similarly, if you point to a square with a gradient going from black in the lower left corner to white in the upper right corner, and ask "what is the angle of that black to white gradient?", the commonest answer will likewise be "45 degrees".
> I think many people, if asked, "on a cartesian grid, what is the relationship between a vector along the Y-axis and a vector at 90 degrees?" would say that they are the same,
Really? I think most would look at you funny and say, "What the heck are you talking about? Speak English, man!" (well, maybe not most; maybe just English speakers would say that). Maybe if you were asking people in a math class or something...
> and surprise might not be enough if told that the Y axis is at MINUS 90 degrees. They may need astonishment.
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> David Singer
> Multimedia and Software Standards, Apple Inc.
I've not heard of any astonishment from people setting gradient directions in Adobe products or in your own company's products (Pages, Keynote).