In article ,
(John Hamilton) wrote:

The lat/long for airports is called the ARP (airport reference point),
usually located near the geographic center of the field. The localizer
is at the far end of the runway. If the approach calls for a DME from
the localizer, you cannot use GPS because there is no coordinate for
the localizer antenna array. Note that for a long runway, like the
11,500 foot long runways at KPIT, it could be more than a mile from
the end of the runway to the ARP.

The FAA is working to determine coordinates for these antennas, I have
heard.

I find it hard to believe that the FAA doesn't know the location of the
localizer antennas down to the fraction of an RCH. Getting that
information published in databases may be a project, but I gotta believe
the information already exists somewhere inside the FAA.