Help with understanding matrices
Help with understanding matrices
- Subject: Help with understanding matrices
- From: Simon Topliss <email@hidden>
- Date: Tue, 12 Feb 2008 18:41:30 +0000
Hello everyone. Is there a maths genius in the room?
I never studied matrices at school and I'm having a great deal of
difficulty understanding how to do matrix calculations.
I tried to read the wikipedia entry but it was way over my head!
http://en.wikipedia.org/wiki/Matrix_(mathematics)
What I'm trying to work out is the rotation and/or scale of an image
placed in Adobe Illustrator CS3.
Getting to matrix of an image when first placed into returns the result:
{class:matrix, mvalue_a:1.0, mvalue_b:0.0, mvalue_c:0.0,
mvalue_d:-1.0, mvalue_tx:-7598.0, mvalue_ty:9058.275390625}
If I rotate the image by 45 degrees clockwise, the matrix is now:
{class:matrix, mvalue_a:0.707106769085, mvalue_b:-0.707106769085,
mvalue_c:-0.707106769085, mvalue_d:-0.707106769085,
mvalue_tx:-1.14441533203125E+4, mvalue_ty:821.1611328125}
And, if I then scale it by 50%, the matrix is now:
{class:matrix, mvalue_a:0.353553384542, mvalue_b:-0.353553384542,
mvalue_c:-0.353553384542, mvalue_d:-0.353553384542,
mvalue_tx:-5511.07666015625, mvalue_ty:559.08056640625}
So, how would I work out what the rotation and scale of the image is
given the values in the second and third results?
What do the "mvalue" numbers define? Is there even a way to get the
rotation and scale from these numbers?
TIA for anyone willing to help me with this.
Simon
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