Retrieving a CGRect from a transformed CGContext and apply to a UIView

Question

I am drawing a PDF page into a CGContext.

In order to properly draw it, I am applying some transformations to the context.

The pdf page rendered rect is smaller than the view's rect.

I want to create a third view that has exact same frame as the part of the view that has a pdf rendered.

My solution works, but not entirely. Sometimes (a lot of times) the rect is wrong.

This is what I am doing:

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)context {
      CGContextSaveGState(context);
      // apply transforms to context
      // draw pdf page

      CGRect calculatedFromRect = CGRectApplyAffineTransform(pageRect, CGContextGetCTM(context));
      CGContextRestoreGState(context);

      // now draw a green rect to test the frame on a not transformed context
      GContextSetFillColorWithColor(context, [UIColor greenColor].CGColor);
      CGContextFillRect(context, calculatedFromRect);

      self.thirdView.frame = calculatedFromRect;
 }

The thirdView is red. When both rects (view and drawing) are equal, I see a brown rect on the screen (red with alpha on top of the green rect). But sometimes I can see they two separated from each other (offset and size difference...when this happens, the thirdView.frame is bigger than calcularedRect).

Since all the involved views have the same size and coordinates, not converting the coordinates with convertRect:fromView: shouldn't be a problem. But I tried this and the result was the same.