How to get actual pdf page size in iPad?

Question

How can I get PDF page width and height in iPad? Any document or suggestions on how I can find this information?

Answer 1

I took Donal O'Danachair's answer and made a few modifications so the rect size is also scaled to the pdf's size. This code snipped actually gets all the annotations off a pdf page and creates the CGRect from the PDF rect. Part of the code is form the answer to a question Donal commented on his.

CGPDFDictionaryRef pageDictionary = CGPDFPageGetDictionary(pageRef);

    CGFloat boundsWidth = pdfView.bounds.size.width;
    CGFloat boundsHeight = pdfView.bounds.size.height;
    CGRect cropBoxRect = CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox);
    CGRect mediaBoxRect = CGPDFPageGetBoxRect(pageRef, kCGPDFMediaBox);
    CGRect effectiveRect = CGRectIntersection(cropBoxRect, mediaBoxRect);

    CGFloat effectiveWidth = effectiveRect.size.width;
    CGFloat effectiveHeight = effectiveRect.size.height;

    CGFloat widthScale = (boundsWidth / effectiveWidth);
    CGFloat heightScale = (boundsHeight / effectiveHeight);

    CGFloat pdfScale = (widthScale < heightScale) ? widthScale : heightScale;

    CGFloat x_offset = ((boundsWidth - (effectiveWidth * pdfScale)) / 2.0f);
    CGFloat y_offset = ((boundsHeight - (effectiveHeight * pdfScale)) / 2.0f);

    y_offset = (boundsHeight - y_offset); // Co-ordinate system adjust

    //CGFloat x_translate = (x_offset - effectiveRect.origin.x);
    //CGFloat y_translate = (y_offset + effectiveRect.origin.y);

    CGPDFArrayRef outputArray;

    if(!CGPDFDictionaryGetArray(pageDictionary, "Annots", &outputArray)) {
        return;
    }

    int arrayCount = CGPDFArrayGetCount( outputArray );
    if(!arrayCount) {
        //continue;
    }

    self.annotationRectArray = [[NSMutableArray alloc] initWithCapacity:arrayCount];

    for( int j = 0; j < arrayCount; ++j ) {
        CGPDFObjectRef aDictObj;
        if(!CGPDFArrayGetObject(outputArray, j, &aDictObj)) {
            return;
        }

        CGPDFDictionaryRef annotDict;
        if(!CGPDFObjectGetValue(aDictObj, kCGPDFObjectTypeDictionary, &annotDict)) {
            return;
        }

        CGPDFDictionaryRef aDict;
        if(!CGPDFDictionaryGetDictionary(annotDict, "A", &aDict)) {
            return;
        }

        CGPDFStringRef uriStringRef;
        if(!CGPDFDictionaryGetString(aDict, "URI", &uriStringRef)) {
            return;
        }

        CGPDFArrayRef rectArray;
        if(!CGPDFDictionaryGetArray(annotDict, "Rect", &rectArray)) {
            return;
        }

        int arrayCount = CGPDFArrayGetCount( rectArray );
        CGPDFReal coords[4];
        for( int k = 0; k < arrayCount; ++k ) {
            CGPDFObjectRef rectObj;
            if(!CGPDFArrayGetObject(rectArray, k, &rectObj)) {
                return;
            }

            CGPDFReal coord;
            if(!CGPDFObjectGetValue(rectObj, kCGPDFObjectTypeReal, &coord)) {
                return;
            }

            coords[k] = coord;
        }               

        char *uriString = (char *)CGPDFStringGetBytePtr(uriStringRef);
        //******* getting the page size

        CGPDFArrayRef pageBoxArray;
        if(!CGPDFDictionaryGetArray(pageDictionary, "MediaBox", &pageBoxArray)) {
            return; // we've got something wrong here!!!
        }

        int pageBoxArrayCount = CGPDFArrayGetCount( pageBoxArray );
        CGPDFReal pageCoords[4];
        for( int k = 0; k < pageBoxArrayCount; ++k )
        {
            CGPDFObjectRef pageRectObj;
            if(!CGPDFArrayGetObject(pageBoxArray, k, &pageRectObj))
            {
                return;
            }

            CGPDFReal pageCoord;
            if(!CGPDFObjectGetValue(pageRectObj, kCGPDFObjectTypeReal, &pageCoord)) {
                return;
            }

            pageCoords[k] = pageCoord;
        }

#if DEBUG
        NSLog(@"PDF coordinates -- bottom left x %f  ",pageCoords[0]); // should be 0
        NSLog(@"PDF coordinates -- bottom left y %f  ",pageCoords[1]); // should be 0
        NSLog(@"PDF coordinates -- top right   x %f  ",pageCoords[2]);
        NSLog(@"PDF coordinates -- top right   y %f  ",pageCoords[3]);
        NSLog(@"-- i.e. PDF page is %f wide and %f high",pageCoords[2],pageCoords[3]);
#endif
        // **** now to convert a point on the page from PDF coordinates to iOS coordinates. 

        double PDFHeight, PDFWidth;
        PDFWidth =  pageCoords[2];
        PDFHeight = pageCoords[3];

        // the size of your iOS view or image into which you have rendered your PDF page 
        // in this example full screen iPad in portrait orientation  
        double iOSWidth = 768.0; 
        double iOSHeight = 1024.0;

        // the PDF co-ordinate values you want to convert 
        double PDFxval = coords[0];  // or whatever
        double PDFyval = coords[3]; // or whatever
        double PDFhval = (coords[3]-coords[1]);
        double PDFwVal = coords[2]-coords[0];

        // the iOS coordinate values
        CGFloat iOSxval, iOSyval,iOShval,iOSwval;

        iOSxval =  PDFxval * (iOSWidth/PDFWidth);
        iOSyval =  (PDFHeight - PDFyval) * (iOSHeight/PDFHeight);
        iOShval =  PDFhval *(iOSHeight/PDFHeight);// here I scale the width and height
        iOSwval = PDFwVal *(iOSWidth/PDFWidth);

#if DEBUG
        NSLog(@"PDF: { {%f %f }, { %f %f } }",PDFxval,PDFyval,PDFwVal,PDFhval);
        NSLog(@"iOS: { {%f %f }, { %f %f } }",iOSxval,iOSyval,iOSwval,iOShval);
#endif


        NSString *uri = [NSString stringWithCString:uriString encoding:NSUTF8StringEncoding];
        CGRect rect = CGRectMake(iOSxval,iOSyval,iOSwval,iOShval);// create the rect and use it as you wish