gistfile1.ps1

function CalculateRelative($path,$pathRelative)
{
    $parts1 = ($path.ToString()).Split("\")
    $parts2 = ($pathRelative.ToString()).Split("\")
    $prefixEqual = 0
    $min = [Math]::Min($parts1.Length, $parts2.Length)
    $continue = $true
    while($prefixEqual -lt $min)
    {
        if ($parts1[$prefixEqual] -ne $parts2[$prefixEqual])
        {
            break
        }
        $prefixEqual = $prefixEqual + 1
    }
    $firstPartCount = $parts1.Length - $prefixEqual
    if ($firstPartCount -gt 0)
    {
       $p1 = [string]::Join("\", (1..$firstPartCount | % { ".."} ))
    } 
    else
    {
       $p1 = ""
    }

    $secondPartCount = $parts2.Length - $prefixEqual
    if ($secondPartCount -gt 0)
    {
       $p2 = [string]::Join("\", $parts2, $prefixEqual, $secondPartCount)
    } 
    else
    {
       $p2 = ""
    }
    
    return [IO.Path]::Combine( $p1, $p2 )
}