Marine Electronics Forum - coordinates

Does anyone have an easy way to convert loran #'s to gps ?

Easy is in the eye of the beholder.* To use this program, you have to know the grid and station numbers you are using.* None of the Loran to GPS conversions are known to be all that accurate.* However, it's a free download.* http://chartmaker.ncd.noaa.gov/MCD/loranc.htm

Slim - 6/2/2004 9:05 PM

Does anyone have an easy way to convert loran #'s to gps ?

Easy? Yes but useful? No.

Cheers, Kerry.

Take your GPS and go into it setup and select LORAN as its map datum or display choice. Save the LORAN numbers you want as waypoints. Now go back to setup in the GPS and change the display choice of map datum (depends on what make and model you have as to where it will be found) to Latitude and Longitude in any of the common formats and the GPS will do the conversion for you.

Be warned, for most of the coast the conversion will not be extremely accurate. By that I mean that you can not take a paper chart and find a point on it, be it a land mark or some fixed object at sea, and determine its location from the LORAN lines on the chart and then go to the indicated numbers and actually find the thing you are looking for. You can do that with Lat/Lon from the chart, but not with LORAN. The reason lies in the inherent inaccuracy of LORAN. The best you can hope for is 1/4 mile accuracy, although you may do better. Just curious, why are you screwing around with LORAN anyway? It was a trash system when it was all we had and it sure hasn't improved any in the years its has been left in disrepair and neglect.

Thom

A lot of very good fishing holes are recorded in Loran TDs.* Also, a lot of offshore old timers still talk in TDs on the radio, and really that's the only thing they know.* Get within a quarter mile and you can study the bathymetric charts, sonar, other boats, and maybe be able to recreate something.*

Thoms idea sounds like a great method. Another thing you could do, is get a Garmin handheld GPS which have built in GPS to Loran converions on them. For example, I have a Rhino 120 radio/gps. It has some amazing software on it to do things like convert Loran to lat/long.....

The best most accurate way is to have the Loran and the GPS on the boat.
Go to the spots with the LoRAN and then enter it into the GPS when your on the spot.
This takes a lot of time, but it is acurate.
There is no conversion, it's direct entry.

You can't convert accurately. You'd be lucky to get within a mile and that's a lot of ground to cover to find a honey hole.

The inaccuracy is not due to the inherrant lack of accuracy of Loran, as Thom stated above. In fact Loran, from the perspective of repeatability (returning to the same spot) is very very good. The conversion problem lies in the fact that the Loran radio signal transmissions are skewed by large*land masses and man made objects. The fact that the algorithms*used to convert Loran to GPS cannot take these factors into consideration is the problem.

That's why I bought a used Loran on eBay and plan to visit these honey holes as the opportunity arises and set a waypoint when I get there. It's the only way to do it.

Without revisiting every TD# and re-saving as Lat/Long, which is the best way to ensure integrity the other way, which although being far from exact might at least get one a little closer but the process must be applied on a reasonably local basis and for each totally different area/location then a different set of adjustments would need to be determined.

One way is to physically locate a good known spot with Loran and save the coordinates with GPS. Compare these saved GPS coordinates to the Lat/Long resulting from the conversion of the TD#'s and derive an adjustment. In theory if this adjustment/difference is then applied to other Lat/Long numbers derived from converting TD#'s then if applied in a localized area the resulting Lat/Long values should be much closer then if just used based on the Loran conversion.

Even without a Loran if one knows the lat/Long as well as TD#'s for a specific spot then within reason within a localised area the shift/adjustment could be determined. Won't be perfect but will certainly be closer than the raw conversion of TD#'s to lat/Long using conversion software.

Must keep in mind that any shift/adjustment is only relevant to the specific area that it is determined for.

Cheers, Kerry.

Slim,
The best program I have found is one called "gps vault". It converts TDs to lat lon fairly accurately using the Navy ASF corrections which vary a great deal in some locations and little in others. I've converted hundreds of old bottom structure locations off the GA coast and have been pleasantly supprised at the accuracy of the conversions. Most have been right on or at least within 100 ft. Don't rely on your gps to do this conversion. They simply do the mathmatical conversion and require you to supply the ASF adjustment if the option is available. I also installed a loran on the boat at a last resort to relocate a bad conversion. I haven't had to use it so far.
Luck
Joe

Same subject, same question, same comments as this one

http://thehulltruth.net/forums/thread-view.asp?tid=28339&posts=10#M311743

Cheers, Kerry.


cancel that wrong place ;?

This is the same method that my buddy and I use here in the Gulf of Mexico. Conversions are not even close...You will spend days looking for a converted number and the only thing you will get out of it is frustration. Go onto eBay and find a decent Loran. Find your numbers with the Loran and a good bottom machine...Then mark them with your GPS...Once all your numbers are converted to good GPS Lat/Lon's....Put the Loran back up on ebay and let the next guy get to work...

kerry that is what the andren software does.