Center Image and Text in NSAttributedString

gistfile1.txt

        // Create text attachment
        NSTextAttachment *textAttachment = [[NSTextAttachment alloc] init];
        textAttachment.image = [UIImage imageNamed:nameicon];
        textAttachment.bounds = CGRectMake(0, 0, 20, 16);
        
        // Attribute
        NSAttributedString *attrStringWithImage = [NSAttributedString attributedStringWithAttachment:textAttachment];
        NSMutableAttributedString *str = [[NSMutableAttributedString alloc] initWithAttributedString:attrStringWithImage];
        
        // Change base line
        [str addAttribute:NSBaselineOffsetAttributeName value:@(-1.5f * ratio) range:NSMakeRange(0, attrStringWithImage.length)];
        
        NSRange rangeImage = [fullText rangeOfString:@"#image#"];
        
        [attributedText replaceCharactersInRange:rangeImage withAttributedString:str];

what is ratio?