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Loran to GPS conversion question

Old 07-21-2013, 06:14 PM
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Question Loran to GPS conversion question

Hi all,

(My 2nd post) - I got good help with the first one re: EZ Anchor pullers, so I'm trying again.

Twenty years ago when I only had a Loran I marked dozens of favorite fishing spots with my Loran in the LAT/LON MODE -- NOT TD'S.

Now that I've resumed fishing that area again I have a GPS, but when I enter the Lat/lon numbers I saved (on hardcopy) from my old Loran I am frequently far off my former locations - some of which I can still determine closely by lining up some of the few remaining land marks in perpindicular directions.
In some instances saved locations (like port entrances), the GPS shows them to be way inland.

Anybody else had this problem - AND FOUND A SOLUTION ?? ;?

Just to repeat -- I saved NOTHING IN TD'S.

Thanks in advance.

Ron
Old 07-21-2013, 07:29 PM
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You need multiple locations in your area that have the tds and gps numbers. Try looking on charts or local fishing clubs. Once you have these numbers you can take all of your numbers that are close to one of your new (# w/td & gps) numbers and use your gps to convert them. Example: If point A is a marker that you know the td & gps number for then you can put your gps in td mode. Drive up to point a and figure out the difference between the two numbers (the actual td # & the td # your machine says) and use that difference to program your machine (by adding or subtracting in td mode) until your machine says the same as point a. Now you can convert all the td #s w/in a 10-15 mile area of point a. After 10-15 miles you start to lose accuracy hence the need for multiple point A locations. You can send your numbers to Andren.com and they will do the same thing using software. It will only be accurate if they have or you send them multiple locations to work off of. Sounds complicated but it is really very simple especially if you know how to use your gps. If not then you will need tp get out your manual and start reading.
Old 07-22-2013, 07:25 AM
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Loran was repeatable (precise) but not accurate. Positions did not transfer well from one unit to another.. When you say they were far off how far? 100 yards? 10 miles? 1/8-1/4 mile is all the accuracy you can expect from LoranC and worse if near obstructions.
Old 07-22-2013, 09:42 AM
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Originally Posted by Capttater View Post
Loran was repeatable (precise) but not accurate. Positions did not transfer well from one unit to another.. When you say they were far off how far? 100 yards? 10 miles? 1/8-1/4 mile is all the accuracy you can expect from LoranC and worse if near obstructions.
^this x2
Old 07-22-2013, 09:49 AM
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Originally Posted by Rhonda Gale View Post
You need multiple locations in your area that have the tds and gps numbers. Try looking on charts or local fishing clubs. Once you have these numbers you can take all of your numbers that are close to one of your new (# w/td & gps) numbers and use your gps to convert them. Example: If point A is a marker that you know the td & gps number for then you can put your gps in td mode. Drive up to point a and figure out the difference between the two numbers (the actual td # & the td # your machine says) and use that difference to program your machine (by adding or subtracting in td mode) until your machine says the same as point a. Now you can convert all the td #s w/in a 10-15 mile area of point a. After 10-15 miles you start to lose accuracy hence the need for multiple point A locations. You can send your numbers to Andren.com and they will do the same thing using software. It will only be accurate if they have or you send them multiple locations to work off of. Sounds complicated but it is really very simple especially if you know how to use your gps. If not then you will need tp get out your manual and start reading.
I agree completely.

This is a copy and paste from an old post I made which is exactly what Rhonda Gale said above but maybe hearing it in two ways will help some:

The old TD numbers I had when entered them on my GPS were WAY off from where I knew the spot was (the little flag markers on the screen) so this is what I did:

I think that most GPS units will accept TDs. There is also (usually?) a screen that accepts "offsets". (Think "set up" in your GPS menu.) Pick a spot that you have both GPS and TD numbers. Switch your GPS to read TDs and select small spot that you KNOW your GPS's location is "right on". The TDs it displays should be somewhat different than your TD numbers from your old LORAN TDs. Subtract the GPS TD numbers from your old LORAN TD numbers and that will give you the "offset". Enter these numbers as +/- numbers in the offset screen on your GPS (I had to play with this a little as to which was + and which was - ). I could then enter the old TD numbers from other sites and they ended up a lot closer to the actual spot. The farther you get from the "offset spot" the less accurate it will be.

That's probably pretty confusing but it's the best I can explain it. Maybe you will get lucky and your TDs will convert without all that but I have found quite a few "old spots" by entering TDs into my GPS unit.

Good luck.
Old 07-22-2013, 11:14 AM
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Originally Posted by Capttater View Post
Loran was repeatable (precise) but not accurate. Positions did not transfer well from one unit to another.. When you say they were far off how far? 100 yards? 10 miles? 1/8-1/4 mile is all the accuracy you can expect from LoranC and worse if near obstructions.
That's exactly what my loran was VERY ACCURATE REPEATABILITY. If I took my time before dropping anchor I could often be within the length of my little boat of where I wanted to be - doing this AT NIGHT!

The reason I'm sure of this is that prior to even Lorans I would find at least two close to perpindicular land marks (each with two objects to line up). And I would end up exactly on them both once it was daylight, most of the time.

I'll have to try following some of the other advice I've received (complicated though some of it seems). It's worth a shot.
Old 07-22-2013, 11:41 AM
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When playing with 'offsets', as I recall the 'offset' for a given waypoint could (and probably was) different on any given day. You also have to remember the only unit that will (would) read LORAN was LORAN. Any waypoint saved as Lat/Lon is in a big ball park at best. And there is no direct conversion within a LORAN or GPS unit , completely different inputs and computations ...
Old 07-22-2013, 05:59 PM
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So are you telling me that I'd be wasting my time to try Rhonda and Gulfer's suggestions (above). Assuming I can follow them(???)

Ron
Old 07-22-2013, 09:13 PM
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Anything is worth a try, just don't get your hopes up. And have plenty of time when attempting to locate stuff on the water ...
Old 07-23-2013, 08:23 AM
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There would have been an unavoidable conversion error when your loran was recording L/L coordinates for you to view even though it was actually storing the loran TD's to repeatably navigate back to. The TD's were fairly accurate but the L/L "titles" were not as accurate.

That conversion error would be seriously compounded, too, if by any chance the L/L degrees, minutes, decimal minutes or seconds format was not copied identically when transferring WP coordinates to the GPS.
(I.e. say, DD-MM-SS on the loran and same numbers input instead as DD-MM.mm on the GPS, ... or vice versa: 41*-43'-52" is not the same latitude as 41*-43.52' .
If... I calculate correctly that particular example creates a N/S latitude error of just over 2100'. And the longitude coordinate would increase the error.)

So you might just confirm identical format, including making sure the coordinates were copied correctly to hard copy from the loran in the 1st place.
Old 07-23-2013, 09:29 AM
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Andren Software, check it out. My friend has been using for a long time and it is very accurate.
Old 07-23-2013, 09:44 AM
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Just get a Humminbird Side Imaging and remap them. And see if there are any fish. You can cover about a 500' swath of water which should be within the error factor.
Old 07-23-2013, 05:15 PM
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Go to rumkin.com and look for degree converter. This may help w/gps numbers. Not tds. I converted about 3,000 numbers using the method I described above. It took over a year as I had to run to a new area each time to get td/gps correction numbers. A friend had a si-tex loran and gps on his boat so we would go to td # and convert to gps. We converted all numbers in a ten mile circle and tried to overlap circles whenever we could to increase accuracy. There is a lot of ocean between st. augustine and cape canaveral. I have conversion numbers for volusia/brevard county. 15 or so for each area still written down. I think you can also find them on the web. No secret spots. PM me if anyone needs them. Leon
Old 07-23-2013, 07:58 PM
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I've been down this road before . . .

There is no accurate conversion.

I ended up buying a HANDHELD LORAN-C off ebay and using it to go to the spots and then saving them on GPS.

I know thats not an option anymore but I can tell you I tried the conversion software, offsets, etc and I never found the spots.

-Rob
Old 07-26-2013, 04:58 PM
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Originally Posted by rbhankins001 View Post
I've been down this road before . . .

There is no accurate conversion.

I ended up buying a HANDHELD LORAN-C off ebay and using it to go to the spots and then saving them on GPS.

I know thats not an option anymore but I can tell you I tried the conversion software, offsets, etc and I never found the spots.

-Rob
I assume that's no longer an option because Loran finally no longer exists ???

FYI: I'm talking SF Bay Area - just in case it's still operative on the left coast.
Old 10-06-2013, 12:09 PM
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I have read about Andren Software. I am not going to buy the software at first, but they have a conversion service they offer for thirty bucks. They say they will convert any amount of numbers for that price. We are getting numbers together to send to them. I will let you know how it works out.
Old 10-11-2013, 08:52 AM
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I still use TD`s..To me more spot on. I set my GPS up in TD`s and don`t use unit to convert old #s. I motor to a spot and store. If I have a long run I use Lat/Lons to nav. and then store as TD`s when I get to where I`m goin. Don`t use old TD #s--some are way off and some are spot on..It`s a crap shoot. Do what u feel.
Capt.Skid
Old 10-12-2013, 06:03 AM
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I purchased Andren software a couple of months ago and have entered over 200 loran numbers that are crossed to gps. It will then take the new gps numbers and upload into your plotter. In the GPS numbers I've been able to check out they are very close.
Old 10-13-2013, 11:13 AM
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This dates me, but similar conversions were attempted when the Decca system was displaced by Loran...

I only saw Decca demonstrated once, on a university research vessel, and remember thinking how cumbersome the system was, and, it used proprietary paper charts with position lines, which the company didn't exactly give away...

Many people much younger than me take GPS, differential GPS, WAAS, etc for granted, and don't even realize how relatively inaccurate it was until Selective Availability (which intentionally diluted precision) was turned off by then President Clinton...accuracy became good enough for street navigation, which was very marginal before that. Many boaters are unaware that GPS provides precision timing signals also, necessary for various things like spread-spectrum radio, and even time-division multiplexing used in all cell phone towers. If the US threw the switch on GPS, we would be in deep shit...the military GPS uses a different band, and is not receivable with commercially available equipment, but is much more accurate than what's available for civilian use. It's what can put a cruise missile down someone's 8" chimney...
Old 10-13-2013, 01:07 PM
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Originally Posted by glassparon View Post
I assume that's no longer an option because Loran finally no longer exists ???

FYI: I'm talking SF Bay Area - just in case it's still operative on the left coast.
Sorry, it's not.

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