powershell function to resolve a file path, expanding any mapped dives to their full UNC path in the process.

Resolve-Fullpath.ps1

function Resolve-FullPath
{
    [CmdletBinding()]
    [OutputType([string])]
    param (
        # The Path to the File or Folder
        [Parameter(Mandatory = $true, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true)]
        [Alias("FullName")]
        [ValidateNotNullOrEmpty()]
        [string]
        $Path
    )
    <#
    .SYNOPSIS
    Resolves the full path to a file or directory, including the UNC path of any mapped drives.

    .PARAMETER Path
    The Path you want to resolve.

    .OUTPUTS
    The fully resolved path as a string.

    .EXAMPLE
    PS> Resolve-FullPath -Path "Z:\tools\Default-BGInfo.bgi" 
    \\storage.lab.local\3rdPartytools\Default-BGInfo.bgi

    #>

    process
    {
        $Location = Get-Item -Path $Path

        if (-not [string]::IsNullOrEmpty( $Location.PSDrive.DisplayRoot))
        {
            $CorrectRoot = "{0}\" -f $Location.PSDrive.DisplayRoot
            Write-Verbose ("The drive root [{0}] resolves to {1}" -f $Location.PSDrive.Root, $CorrectRoot)

            $Location.FullName.Replace($Location.PSDrive.Root, $CorrectRoot)
        }
        else
        {
            $Location.FullName
        }
    }
}