SUBJECT: # 32189: loran number conversions to gps

Submitted by Billy S (209.86.155.228) from GEORGIA on 9/21/2000 11:23:00 AM

Can anyone tell me how to convert td's to gps lat/lon's.My lowarance 2000 does not convert loran numbers. Is there a web site set up for this yet?

1. 9/21/2000 11:31:00 AM Submitted by Jeff K. (198.26.132.101) from VIRGINIA says Loran to GPS conversion
   You can download a program that will do the conversion from www.rdc.uscg.mil/rdcpages/soft-posaid2.html. It works pretty well, as far as I can tell. You must give it the Loran chain to use and a "seed" Lat/Lon close to the location. It also gives you options on the type of map datum for the Lat/Lon output.

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2. 9/21/2000 12:37:00 PM Submitted by KenG (166.96.254.4) from NEW JERSEY says Didn't work well for me....
   There are lots of variablilites in the loran calculations, and all the conversion programs are an approximation - 1000 feet in my experience (plus the variations in loran are dependent on your geographic location). If you are just doing landmarks, no problem. But I was converting wreck locations, and the conversions were useless. I checked the conversions against my old loran numbers and my new DGPS numbers - the converted numbers I had were so far off they were unuseable. Ken

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3. 9/21/2000 12:46:00 PM Submitted by Run N' Gun (4.21.194.130) from FLORIDA says New hand held will do the conversions
   Saw in Sportfishing Mag that a new hand help unit that takes TD's and lat/lon's will let you convert the numbers out on the water with precision. I may get one (if they work) because I have a lot of TD's that have not converted very well. It may have been a Magellan but can't say for sure.

   BTW, hope someone replies to my request below about Charleston. Need to decide. Tight lines.

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4. 9/21/2000 3:37:00 PM Submitted by Thom (208.1.148.67) from WEST VIRGINIA says You Need To Understand
   None of the conversion programs will work very well for some locations and in fact will be so far off in some cases to be absolutly worthless. The problem isn't in the conversion programs themselves, they are pretty simple really, and its not with any mysterious vairables either. The problem is with the LORAN system itself. You see, although you get great repeatability with LORAN what you don't get is a very good actual location. On the best day it ever ran you couldn't expect precision greater than a quarter mile (really - look at one of the old User's Manuals for any of them) out of one. What that means is that if you were to go to a a spot on the earth who's location was known with great precision and get a fix from a LORAN while standing there you could't expect the location it indicated to be any closer than the quarter mile I mentioned. By contrast any GPS would indicate the correct position within about 30-50 feet. So the problem you face is this, the conversion programs will show you the location that the LORAN would have indicated had it been accurate. Unfortunately its inaccuracy is what confuses the issue. Make sense? What all that means is that it doesn't matter if you use PosiAid-II (the Coast Guard's conversion program) or just convert using your GPS (most all of them will do it) you're still not going to get a very good representation. Oh, there are some areas where they do work and you can tell which ones these are going to be pretty easily. Just take a look at a chart for the area where the numbers are. If the X and the Y LORAN grid lines cross each other at a 90 degree angle it will be pretty accurate - the farther off from 90 degrees they are the less accurate the original LORAN numbers are.

   Thom

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5. 9/22/2000 10:16:00 AM Submitted by Billy S (207.69.12.154) from GEORGIA says gps conversions
   Thanks for your comments. I need to run the numbers and then put them into my gps for accuracy.

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6. 9/23/2000 3:20:00 AM Submitted by Dunk (208.243.170.159) from NEW JERSEY says Thom's Song And Dance
   Thom, if you admit it or not the offshore fishing field is still divided up in "Loran" numbers. You as a trolling type fisherman have real guts talking about Loran in 1/4 mile "on it's best day numbers" Your talking towers mounted on tera-ferma. Unless you are looking for numbers inland where the loran signal get's bent, Loran is/was accurate.

   Thom you mention repeatability and of course Loran is top's in this area(Mid Atlantic), but to say you don't know where you are is nuts. I've never had a problem relating my position from the Loran to a Map?? Do you?? In fact it's the other way. I look at map...plug in Loran numbers into the machine and I get a heading....to those numbers.. Yes, the old manuals tell you 1/4 mile, but don't try to get us to swallow that....My number here off Jersey are 30ft. Believe me you can't fish on top of a Volkswagon(and smaller) with 1/4 mile numbers.

   Yeah now say "repeatability"...I could/can take these numbers to any other boat/machine and plug them in and land 30ft from the numbers.

   Thom you need to field learn Loran before you trash it. On the other hand I need to field learn GPS, which might be worth doing now that is as accurate as Loran. But for someone that trolls all you do is use it for reference point or get to a certain area.

   Billy, you'll never find your exact Loran numbers with any puter program. If you are talking wrecks where you need to be right on the money you'll have to have both machines on the boat(Loran and GPS) then lock the GPS to the Loran numbers. Even at that you'll still be riding around looking for your bottom with GPS.. Dunk

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7. 9/23/2000 4:49:00 PM Submitted by Erik (15.255.176.47) from CALIFORNIA says Thom is right
   Loran can have really lousy accruacy while still having good repeatability. I used some loran numbers from friends for shallow water rockfish, 100 yds off shore, that would have put me about 100 yds up on the beach. Some units let you correct this offset, others don't.

   The east coast seems to be hanging on to loran TDs. Out here on the west coast I haven't heard a TD used in a couple of years.

   Taking both machines on the boat is the way to go. Now that selective availability has been turned off, GPS is usually good to 20' or so. Differential GPS will do better than that in many areas.

   Erik

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8. 9/24/2000 9:51:00 AM Submitted by Thom (205.245.79.124) from WEST VIRGINIA says Trash It Isn't Exactly The Right Word
   Actually I finally took mine off the boat and sold it about 2 months ago. I kept it just because of all the dinosaurs where I fish. I think I'm going to try to help bury the beast though and, as Eric alludes to, just use the more appropriate notation for location in the future.

   Actually all I was trying to do was explain to Billy S why it couldn't expect exact matches from PosiAid or any other converions program, be it external and loaded on a home computer or internal to whatever brand GPS he had in hand. I think its important for folks to understand that the problem isn't in their conversion program and its not in their GPS, its in the system they are trying to convert from. That saves folks from being dissapointed with perfectly good equipment that they might otherwise thing is operating incorrectly. Sorry if this riled your feathers.

   In terms of taking locations off charts and putting them in whatever machines this is interesting to note: Even on large scale NOAA charts (1:80,000) you find the latitude scale for nautical miles is marked down to a tenth of a mile (608 feet) which means that anyting you are trying to lift off the map that is to be closer than that has to be estimated. The TD intersect lines, on the other hand, are marked increments of 10 (which equals about 1.2 nautical miles in in the mid atlantic region) and so any thing you try to take from the map that is to be more accurate than that is just an estimate by the person doing the lifting. Sort of shoots the idea that you can get more accurate numbers from a chart for use with the LORAN right in the foot. Oh, while we have the charts out - take a look at the disclaimer for the LORAN overlay (they all have it and its always exactly the same) and you'll see that you shouldn't expect accuracy greater than a 1/4 mile, as per Coast Guard requirments for LORAN accuracy - just an interesting sidenote.

   Its no secret how I feel about LORAN though. Its a garbage system, always was and will continue to be until the Congress gets some sense and quits funding it entirely - soon I hope. In truth with the demise of SA there is absolutly no reaon on earth for anyone to be using that antiquated system these days and with GPS accuracy down to 10 meters or less for both absolute positon accuracy and repeatability there's no good argument at all anymore for keeping a LORAN - other than the operator was to lazy to convert their numbers.

   Whatever ...... have a nice day

   Thom

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