html - How to track users origin PHP by using example.com/index.php?ref=origin -

how track users origin in php , see people using ref= don't have idea how request works .

my code

 $calling_url = mysql_real_escape_string($_server['http_referer']); 

url:

http://example.com/index.php?ref=http://externalsite.com/page.html or
http://example.com/index.php?ref=http%3a%2f%2fexternalsite.com%2fpage.html

php:

$ref = mysql_real_escape_string(rawurldecode($_get["ref"])); // $ref "http://externalsite.com/page.html" in both cases 

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resources url tracking:

• using referrer urls better understand visitors
• referrers , search engines tracking
• alternative $_server['http_referer'] php variable