how to find the degree of rotation?

Lolalola · Postby **Lolalola** » Fri Jul 29, 2011 6:22 pm

Hi,
how to find the degree of rotation?

I find this sample:
http://www.w3.org/TR/SVG/coords.html"codebox">

[transform] => matrix(0.97723057,0.21218012,0.21218012,-0.97723057,90.7988,553.69995)
[id] => text4151
[tspan] => Array
   (
      [value] => Some text some text
      [style] => fill:#231f20;fill-opacity:1;fill-rule:nonzero;stroke:none;font-family:Arial;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:9.99999413;writing-mode:lr;-inkscape-font-specification:Arial
      [x] => 0 6.25999632 12.64999257 17.11998994 22.3099869 26.50998443 30.20998226 36.71997843 43.30997456 46.52997267 51.77996959 57.25996637 60.47996448 66.20996111 72.71995729 77.65995439 84.05995063 88.66994792 93.1299453 99.71994143 102.93993954 107.44993689 111.98993422 115.20993233 120.03992949 126.41992575 131.38992283 136.07992007 141.79991671 144.48991513 149.04991246 152.26991056 156.33990817 161.76990498 168.2199012 178.54989513 183.75989207 189.69988858 192.91988669 203.20988064 209.97987667 213.88987437 220.4798705 223.69986861 234.1098625 239.10985956 243.98985669
      [y] => 0
      [sodipodi:role] => line
      [id] => tspan4153
   )

chriswww · Postby **chriswww** » Mon Aug 01, 2011 4:44 pm

not sure exactly what your question is.
the code you've pasted is a nested transform...a rotation only transform would have last two numbers as zero.
anyhow.
pure rotation matrix is given by (cos(a), sin(a), -sin(a), cos(a), 0, 0)
to get at the angle-since it's constant-just do an inverse operation on one of those numbers.
in your example, say do arcsine of 0.97723057, which is 12 with some decimal places....not sure if you need to convert to/from radians..been a long time since high school trig. some simple testing with inkscape and a calculator handy should confirm.
if that doesn't answer the question...specify what you're trying to accomplish.

LiquidAsh · Postby **LiquidAsh** » Sat Nov 19, 2011 11:09 pm

If you're trying to calculate this from code, use angle = arctan2(sin(angle),cos(angle)) = arctan2(0.21218012,0.97723057). This way you don't have to worry about which quadrant your angle is in.

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how to find the degree of rotation?

how to find the degree of rotation?

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Re: how to find the degree of rotation?

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