ios 에서 pixel to point , point to pixel 로 변환하는 방법

+ (CGFloat)pixelToPoints:(CGFloat)px
{
    CGFloat pointsPerInch = 72.0;
    CGFloat scale = 1;
    float pixelPerInch; // DPI  
   if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
        pixelPerInch = 132 * scale;  
   } else if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone) {
        pixelPerInch = 163 * scale;  

    } else {
            pixelPerInch = 160 * scale;
    }  
   CGFloat points = px * pointsPerInch / pixelPerInch;
    return points;
} 

+(CGFloat) pointsToPixels:(float)point
{
    float pixel; //ipad  
   if ( UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad ){
        pixel = point / 0.54545455;
   }else{
        //iphone
        pixel = point / 0.44171789;
    }  
   return pixel;
}