Re: Loran TD Coordinates to GPS Coordinates Conversions

[ Follow Ups ] [ Post Followup ] [ Great Lakes Shipwreck Research Group ] [ FAQ ]

Posted by Brendon Baillod on August 15, 19101 at 15:15:31:

In Reply to: Loran TD Coordinates to GPS Coordinates Conversions posted by Jerald Boettcher on August 15, 19101 at 11:38:06:

Hi Jerald,

There is a website that I posted on the newsgroup a few years ago that will do the mathematical conversion between TDs and GPS. However, you should be aware that converted numbers are almost useless. They can be off by over a mile in some places. This is because of the land mass propogation error inherent in TDs. The time delays for the old LORAN signals are altered by the radio signals having to pass over land masses and are subsequently non-uniform. Because of this, when your GPS or a computer algorhythm does the conversion from TDs to GPS, it is estimating the GPS based on the assumption that there is no propogation error (there usually isn't any over the oceans). In the Great Lakes however, the propogation error is particularly pronounced because of all the land masses. For a detailed discussion of this, see my online paper at http://www.execpc.com/~bbaillod/navi.html

Unfortunately, there is really no sure fire way to get GPS from TDs. Most divers take their LORAN receiver and GPS to a wreck so they can get GPS numbers. There is currently a major effort to visit all wrecks for which only TDs exist in order to get GPS numbers before LORAN is turned off.

I would actively discourage you from converting the TDs to GPS. I say this because people doing this type of conversion have introduced a lot of bad numbers into circulation and have caused many divers a great deal of frustration and lost dive time. If you do convert these numbers, please indicate that they are estimates done with a conversion so they don't end up in someone's dive log or end up in general circulation as good numbers.

An additional note: Now that the US government has turned off selective availability for GPS units, I have found that many numbers I took with a GPS unit in the 1990s are now somewhat off. The error I have noticed has been as great at 500 ft. Subsequently, I am also trying to revisit wrecks with selective availability impaired GPS in order to get new, accurate readings.

Brendon Baillod
brendon@baillod.com
Great Lakes Shipwreck Research Foundation, Inc
A Non Profit Organization
Host of the Annual Ghost Ships Festival
www.ghost-ships.org

: I am looking for a fabled (or maybe not) website that
: provides Loran to GPS conversions simply by punching in
: the numbers.

: Has anybody out there seen or have had any experience with such a site?

Follow Ups:

Post a Followup

Name:
E-Mail:

Subject:

Comments:
: Hi Jerald, : There is a website that I posted on the newsgroup a few years ago that will do the mathematical conversion between TDs and GPS. However, you should be aware that converted numbers are almost useless. They can be off by over a mile in some places. This is because of the land mass propogation error inherent in TDs. The time delays for the old LORAN signals are altered by the radio signals having to pass over land masses and are subsequently non-uniform. Because of this, when your GPS or a computer algorhythm does the conversion from TDs to GPS, it is estimating the GPS based on the assumption that there is no propogation error (there usually isn't any over the oceans). In the Great Lakes however, the propogation error is particularly pronounced because of all the land masses. For a detailed discussion of this, see my online paper at http://www.execpc.com/~bbaillod/navi.html : Unfortunately, there is really no sure fire way to get GPS from TDs. Most divers take their LORAN receiver and GPS to a wreck so they can get GPS numbers. There is currently a major effort to visit all wrecks for which only TDs exist in order to get GPS numbers before LORAN is turned off. : I would actively discourage you from converting the TDs to GPS. I say this because people doing this type of conversion have introduced a lot of bad numbers into circulation and have caused many divers a great deal of frustration and lost dive time. If you do convert these numbers, please indicate that they are estimates done with a conversion so they don't end up in someone's dive log or end up in general circulation as good numbers. : An additional note: Now that the US government has turned off selective availability for GPS units, I have found that many numbers I took with a GPS unit in the 1990s are now somewhat off. The error I have noticed has been as great at 500 ft. Subsequently, I am also trying to revisit wrecks with selective availability impaired GPS in order to get new, accurate readings. : Brendon Baillod : brendon@baillod.com : Great Lakes Shipwreck Research Foundation, Inc : A Non Profit Organization : Host of the Annual Ghost Ships Festival : www.ghost-ships.org : : I am looking for a fabled (or maybe not) website that : : provides Loran to GPS conversions simply by punching in : : the numbers. : : Has anybody out there seen or have had any experience with such a site?

Optional Link URL:
Link Title:
Optional Image URL:

[ Follow Ups ] [ Post Followup ] [ Great Lakes Shipwreck Research Group ] [ FAQ ]