Rotating CGPoints; CIVector CGAffineTransform?

Question

I have 4 CGPoints that form an irregular figure. How can I rotate that figure 90-degrees and get the new CGPoints?

FWIW, I was able to "fake" this when the figure is a CGRect by swapping origin.x and origin.y, and width and height. Will I need to do something similar (calculating distance/direction between points) or is there a AffineTransform I can apply to a CIVector?

Hints and/or pointers to tutorials/guides welcome.

Skippable Project Background:

Users will take pictures of documents and the app will OCR them. Since users have a great deal of trouble getting a non-skewed image, I allow them to create a 4-point figure around the text body and the app skews that back to a rectangle. The camera images coming in are CIImages and so have their origin already in lower-left, so the 4-point figure must be rotated from the UIView to match...

Answer 1

For the record, I used CGAffineTransforms to rotate the points:

CGAffineTransform t1 = CGAffineTransformMakeTranslation(0, cropView.frame.size.height);
CGAffineTransform s = CGAffineTransformMakeScale(1, -1);
CGAffineTransform r = CGAffineTransformMakeRotation(90 * M_PI/180);
CGAffineTransform t2 = CGAffineTransformMakeTranslation(0, -cropView.frame.size.height);

CGPoint a = CGPointMake(70, 23);
a = CGPointApplyAffineTransform(a, t1);
a = CGPointApplyAffineTransform(a, s);
a = CGPointApplyAffineTransform(a, r);
a = CGPointApplyAffineTransform(a, t2);

&c. for the other points.