Comments on: EXIF Parser

By: Anders Borg

Anders Borg — Fri, 10 Jul 2009 23:03:31 +0000

Sorry. Forgot to remove the line breaks from previous use of print and . This is the way it should be:

$latitude = decimalcoord($exif['GPSLatitude']);
$longitude = decimalcoord($exif['GPSLongitude']);
// Adjust also above values to the “Ref” settings

function decimalcoord($values)
{
return divide($values[0]) + divide($values[1]) / 60 + divide($values[2]) / 3600;
}

function divide($value)
{
$values = explode(“/”, $value);
return $values[0] / $values[1];
}

By: Anders Borg

Anders Borg — Fri, 10 Jul 2009 23:01:09 +0000

Here’s a more elegant solution (IMO) to calculating correct decimal coordinates:

$latitude = decimalcoord($exif['GPSLatitude']) . “\r\n”;
$longitude = decimalcoord($exif['GPSLongitude']) . “\r\n”;
// Adjust also above values to the “Ref” settings

function decimalcoord($values)
{
return divide($values[0]) + divide($values[1]) / 60 + divide($values[2]) / 3600;
}

function divide($value)
{
$values = explode(“/”, $value);
return $values[0] / $values[1];
}

By: Kevin

Kevin — Thu, 15 Jan 2009 22:19:14 +0000

It looks like you’re ignoring the scaling factor (denominator) that is present in the GPSLatitude and GPSLongitude fields. The usual case seems to be that these will be 1 except for the minutes of angle, which is usually 100. Updated code to handle this usual case:

return $deg + ( $min / 6000 ) + ( $sec / 3600 );

It’s important to note that this is still not entirely correct according to the Exif v 2.2 specifications, see pages 53 (GPSLatitude and GPSLongitude) and page 20 (rational data type):

http://www.kodak.com/global/plugins/acrobat/en/service/digCam/exifStandard2.pdf

A more correct solution would be modifying ConvertFractionToDecimal as follows:

function ConvertFractionToDecimal ( $fraction )
{
if ( !isset ( $fraction ) )
return 0;

$dividerPosition = strpos ( $fraction, ‘/’ );

if ( $dividerPosition === false )
return $fraction;

return substr ( $fraction, 0, $dividerPosition ) / substr ( $fraction, $dividerPosition + 1 );
}

This would allow any scaling factor/denominator to be used, as per Exif specs.

By: Evert

Evert — Tue, 27 Nov 2007 21:58:21 +0000

thanks that was helpful..

btw.. the ExifConvertDegMinSecToDD can be simplified.. simply change it to:

return $deg + ($min / 60) + ($sec / 3600);

By: Poco

Poco — Thu, 06 Apr 2006 08:35:29 +0000

Hmmm, I like it, I’m still new to PHP and learning as I go. I will file that one away. Thanks for the feedback.

By: Scott

Scott — Thu, 06 Apr 2006 01:12:21 +0000

Howdy, Thanks the code for the Cannon ISO was very helpful, I did it a little differently though. : ) $ISORatings = array(15=>'Auto', 16=>'50', 17=>'100', 18=>'200', 19=>'400'); if (isset($varRawEXIF['ISOSpeedRating'])){ $newEXIFData['ISO Speed'] = $varRawEXIF['EXIF']['ISOSpeedRatings']; }else if(isset($varRawEXIF['MAKERNOTE']['ModeArray'][16])){ $newEXIFData['ISO Speed'] = $ISORatings[$varRawEXIF['MAKERNOTE']['ModeArray'][16]]; }