Groups > comp.lang.java.programmer > #31901

Re: Image rotation part 2

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From	Martin Gregorie <martin@address-in-sig.invalid>
Newsgroups	comp.lang.java.programmer
Subject	Re: Image rotation part 2
Date	Tue, 30 Jun 2015 20:52:56 +0000 (UTC)
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On Tue, 30 Jun 2015 16:20:17 -0400, Eric Sosman wrote:

>      I've used them a few times, but find them confusing -- in part
> because the Y axis is inverted from The Way We Learned In School, which
> is The Way I Always Picture It In My Foggy Little Brain.
>
I'm OK with that part due to a lot of time spent working with 
alphanumeric terminals - VT52, VT100, WY-120 etc. They all treat the top 
left corner of the screen as the origin.

> 	1) Translate the center of your image to the origin, 2) Rotate the
> 	image a quarter-turn (rotation about the
> 	   origin is now rotation about the image's center),
> 	3) Translate the origin to the center of the new image.
> 
> You can build these three transforms (it would take me a few tries to
> get the translations right; see Y axis, above) and combine them into a
> single transform (it would take me a few tries to get the order right;
> matrix multiplication is not commutative but at least you know that the
> rotation step is in the middle), and then apply the combined super-
> transform to your image.
>
Good advice. Thanks. I'll look at that tomorrow.
 

-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

Thread

Image rotation part 2 Martin Gregorie <martin@address-in-sig.invalid> - 2015-06-30 16:55 +0000
  Re: Image rotation part 2 Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-06-30 14:03 -0400
    Re: Image rotation part 2 Martin Gregorie <martin@address-in-sig.invalid> - 2015-06-30 20:04 +0000
      Re: Image rotation part 2 Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-06-30 16:20 -0400
        Re: Image rotation part 2 Martin Gregorie <martin@address-in-sig.invalid> - 2015-06-30 20:52 +0000
  Re: Image rotation part 2 e.d.programmer@gmail.com - 2015-06-30 12:07 -0700
  Re: Image rotation part 2 Martin Gregorie <martin@address-in-sig.invalid> - 2015-06-30 20:18 +0000
  Re: Image rotation part 2 Jeff Higgins <jeff@invalid.invalid> - 2015-06-30 19:04 -0400
    Re: Image rotation part 2 Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2015-06-30 16:36 -0700
      Re: Image rotation part 2 Jeff Higgins <jeff@invalid.invalid> - 2015-06-30 20:17 -0400
    Re: Image rotation part 2 Jeff Higgins <jeff@invalid.invalid> - 2015-06-30 20:09 -0400
    Re: Image rotation part 2 e.d.programmer@gmail.com - 2015-07-01 06:06 -0700
      Re: Image rotation part 2 FredK <fred.l.kleinschmidt@gmail.com> - 2015-07-01 10:57 -0700
      Re: Image rotation part 2 Jeff Higgins <jeff@invalid.invalid> - 2015-07-01 18:13 -0400
      Re: Image rotation part 2 Arne Vajhøj <arne@vajhoej.dk> - 2015-07-27 22:28 -0400
        Re: Image rotation part 2 e.d.programmer@gmail.com - 2015-07-28 04:58 -0700
          Re: Image rotation part 2 Arne Vajhøj <arne@vajhoej.dk> - 2015-07-28 18:58 -0400
            Re: Image rotation part 2 e.d.programmer@gmail.com - 2015-07-29 05:35 -0700

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