[metapost] Hello: possible error in MetaPost tutorial

Dan T. Abell dabell at bikerider.com
Tue Mar 6 20:32:49 CET 2012

Yes, you're right about the sense of rotation. The caption
definitely conflicts with the figure.


On 6 Mar 2012, at 04:39, Shriramana Sharma wrote:

> Hello I'm new to TeX/Metapost. In fact I'ven't even started using them
> yet but planning to do so for a font project. I'll be having highly
> noob questions (but I will make best attempts to do my homework before
> asking). I request the kind help of the people here. Thanks.
> So I was looking at:
> http://www.tlhiv.org/MetaPost/tutorial/tutorial.html where it says:
> "In mathematics as in MetaPost, the positive sense of rotation is
> counterclockwise. Thus the red halfcircle is obtained (from the black
> one) by a rotation of -90 degrees, whereas the blue halfcircle is
> obtained by a rotation of 90 degrees. "
> But the red circle is actually rotated by anticlockwise rotation and
> the blue circle by clockwise rotation. Thus the sign of the values
> should be reversed. Even the commands read:
>  draw halfcircle scaled 2u rotated 90 shifted (1.5u, 4u) withcolor red;
>  draw halfcircle scaled 2u rotated -90 shifted (1.5u, 3u) withcolor blue;
> I hope I'm right. I found a mail ID for the author and am cc-ing to
> them too, in (the unlikely) case that they are not on the list.
> -- 
> Shriramana Sharma
> --
> http://tug.org/metapost/

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