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Thread: Free Loran Conversion Software

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    Default Free Loran Conversion Software

    Isn't there a free download out there that will do rough conversions from TD to lat/lon? I have a loran, just want rough lat/lon on some TD's so I can put them in Mapsource.

    Thanks.

    Dave

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    Quote Originally Posted by Surface Tension View Post
    Isn't there a free download out there that will do rough conversions from TD to lat/lon? I have a loran, just want rough lat/lon on some TD's so I can put them in Mapsource.

    Thanks.

    Dave
    The free download I remember seeing was a dos based application and had no accuracy to it at all.

    The only two programs I know out there that perform the conversions well and allow the user to input calibrations to improve accuracy are

    1) www.andren.com LoranGPS
    2) Offshore Hunter

    I personally use Andren's LoranGPS, and will have to say, it works well. Other's have used Offshore Hunter and have reported success also.

    Dave,

    If the numbers are out of Sebastian, I can convert them for you using LoranGPS and get them back to you in a mapsource file, definitely within 100 ft and typically within 30 feet accuracy. Having them in excel or .txt format will make the pre-conversion process quick.
    Last edited by inletsurf; 04-29-2008 at 02:03 PM.
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    And what about Loran C Numbers. How does one convert those numbers into lat/lon numbers for a regular GPS?

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    That was the dos-based application I was talking about. It has too much error.

    Quote Originally Posted by FeAr_ThE_SpEaR View Post
    And what about Loran C Numbers. How does one convert those numbers into lat/lon numbers for a regular GPS?
    We are talking about Loran C.
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    Default andren software

    I use andren software it converts good highly recommend

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    my furuno navnet says it can convert TD's to GPS.

    ............anyone know how?
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    Quote Originally Posted by KEYSKILLER View Post
    my furuno navnet says it can convert TD's to GPS...........anyone know how?
    Many units are capable of converting TD's to GPS, but from my exerience, few of them do it accurately enough to be effective. I have had very good results with my Andren Loran Program converting TD's quite accurately. Once you locate a couple of your spots and you determine a common bearing & distance correction, the repeatability is quite good. Also, Andren also has a "calibration feature" in his software which allows you to input the accurate conversion (once you locate a spot) and this new calibrated number will convert the entire file more accurately.
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    I have been running the Andren software for about 8 years, and like it very much. Once you fine tune the conversion with the correction factors, the conversions are often within 100' or less, provided that the loran TDs were accurate to begin with.

    You may need to establish several sets of correction factors, however, if you range over a larger area. I have noticed that sometimes the correction factors which work well in one general area can be a little off at a spot 30 miles away. Particularly if a big part of that 30 miles is land. If I understand correctly, this is because the loran signal from land based towers is distorted slightly as it passes different geographical features, which is a big part of what makes a direct, accurate, conversion difficult.

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    Quote Originally Posted by KEYSKILLER View Post
    my furuno navnet says it can convert TD's to GPS.

    ............anyone know how?
    Yes, it has the basic USCG algorithm and secondary ASF's in its system to make the initial conversion. Then you have the ability to enter hard offsets to further fine tune these conversions. The northstar units are the best at this I hear, and I'm guessing they may have a built-in "fine tuning" database for calibration offsets with their internal maps.
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    Here's some threads that explain the Andren software better for those interested...

    http://www.spearboard.com/showthread.php?t=34806
    http://www.spearboard.com/showthread.php?t=21604

    And here's an excerpt from Carl Andren discussing the topic, in his own words:

    Quote Originally Posted by Lyman-Reefrat
    You can get good conversions to nearly the accuracy of loran, but you have to calibrate to get it.

    First, let me examine the question of accuracy of the original Loran readings. If you take a NOAA chart with Loran lines (or one of these programs) and check the line spacing per 0.1 microseconds, you get a spacing of 48 feet for the 7980Y lines and 74 feet for the 7980Z lines in the Sebastian Inlet area. This means that the loran number will increase by one 0.1 digit for every 48 feet traveled in the 340 degree direction or 74 feet in the 240 degree direction. Therefore, one could say that, in this area with its' excellent geometry, the resolution of the original data is on the order of 60 ft or so. No amount of conversion to GPS will make it any better. If you have loran data with two digits after the decimal point, then the accuracy will depend more on the real accuracy of the loran set that read the data. We see different brands of loran disagree by as much as 0.2 us, so this increased resolution may not result in better absolute accuracy if you mix readings from several sources. I always tell people to not expect better than 70 ft accuracy for loran in the best case. In the East Texas area, the ratio of the line spacing is almost 10:1 rather than the 1.5:1 as seen here. Therefore, the accuracy of loran in East Texas is poor in one direction and good in the other.

    Now, consider the conversion process, the biggest problem is the fixed bias in the loran readings. Both loran and GPS do what might be called triangulation by measuring range. They measure range by the time difference of arrival (TDs) of two radio signals. Radio signals nominally travel at the speed of light in a vacuum. The GPS signals travel mostly in space and only a small percentage through the atmosphere. The GPS signals are slightly slowed and bent by refraction in the atmosphere, but that small error is corrected for by the DGPS or WAAS systems and would only cause 100 ft or so of error if left uncorrected. The loran signals, however, travel the nap of the earth. They also bend around the earth since the transmitter and receiver are both close to the earth. The loran signals is a long wave signal (2 mile wavelength) unlike GPS that has an 8 inch wavelength. Your receiver sits a few feet above a conductive surface that causes a drag on the loran radio wave. Depending on where you are, the signal may have traveled over dry land, wet land, lakes, cities, and salt water. These all have differing drag effects. That can change the delay by as much as 5 microseconds relative to one that traveled the same distance over salt water. This would place you as much as a half mile off if left uncorrected. This delay is fortunately stable so the loran numbers do not change over time. Therefore, the loran system is very good at finding the same spot time after time to within 70 ft or so. The correction factors for this effect are called Additional Secondary Factors (ASFs). They were estimated and placed in tables by NOAA back in the 1980s. Since they are an estimate there is only about 250 ft of accuracy in the tables. However, once you know a few points where you have both the loran and GPS numbers, then you can calculate the ASFs accurately and get much better conversions. This can be done manually with simple program such as POSAID or automatically with a more complex program.

    Loran numbers observed on land are much more effected by nearby disturbances like power lines, so I will not venture to make a conversion for Capt Jay. The NOAA ASF tables stop at the shoreline and are not applicable on shore.

    The last that I heard was that loran was good through 2008 in the USA. The International Loran Association says that Loran is expanding in Europe and that the US government is considering Loran as a useful backup to GPS. So, it may not go away for a while but may re-emerge as E-Loran. Like Kevin, I use both Loran and GPS on my boat, but unlike him, I plug the converted number in to the GPS to navigate to the spot. I have calibrated my conversions very well and they get me as close as the Loran could. Also, my autopilot only interfaces to the GPS, not the old Loran.

    In closing, I maintain that, in my experience, I can find my spots off Sebastian Inlet as easily with converted numbers in my DGPS as with my loran set. Of course, once I get the DGPS reading, then I can find them even better.
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    more:
    Quote Originally Posted by Lyman-Reefrat
    To begin, let me acknowledge that, like Offshore Hunter I also sell a program that does loran to GPS conversion along with readings management. I will avoid a sales pitch and stick with the issue. I argue that you can get good conversions to nearly the accuracy of loran, but you have to calibrate to get it.
    First, let me examine the question of accuracy of the original Loran readings. If you take a NOAA chart with Loran lines (or one of these programs) and check the line spacing per 0.1 microseconds, you get a spacing of 44 feet for the 7980W lines and 108 feet for the 7980Y lines in the Florida panhandle area. This means that the loran number will tick over one 0.1 digit for every 108 feet traveled in the 350 degree direction or 44 feet in the 80 degree direction. Therefore, one could say that, in this area, the resolution of the original data is on the order of 70 ft or so. No amount of conversion to GPS will make it any better. If you have loran data with two digits after the decimal point, then the accuracy will depend more on the real accuracy of the loran set that read the data. It has been noted that we see different brands of loran disagree by as much as 0.2 us, so this increased resolution may not result in better absolute accuracy. I always tell people to not expect better than 70 ft accuracy for loran in the best case. In the East Texas area, the ratio of the line spacing is almost 10:1 rather than the 2:1 as seen here. Therefore, the accuracy of loran in East Texas is pretty poor in one direction and OK in the other.

    Now, consider the conversion process, the biggest problem is the fixed bias in the loran readings. Both loran and GPS do what might be called triangulation by measuring ranges. They measure range by the time difference of arrival (TDs) of two radio signals that nominally travel at the speed of light. The GPS signals travel mostly in space and only a small percentage through the atmosphere. The GPS signals are slightly slowed and bent by refraction in the atmosphere, but that small error is corrected for by the DGPS or WAAS systems and would only cause 100 ft of error if left uncorrected. The loran signals, however, travel the nap of the earth and bend around the earth since the transmitter and receiver are both close to the ground and the signals either have to go through the earth or around it. The loran signals is a long wave signal with a 2 mile wavelength unlike GPS that has an 8 inch wavelength. Your receiver sits just feet above a conductive surface that causes a drag on the loran radio wave. Depending on where you are, the signal may travel over dry land, wet land, lakes, cities, and salt water. These all have differing drag effects and that can delay the wave by as much as 5 microseconds relative to one that traveled the same distance over salt water only. This would place you as much as a half mile off if left uncorrected. This delay is fortunately stable and the loran numbers do not change over time. Therefore, the loran system is very good at finding the same spot time after time to within 70 ft or so. The correction factors for this effect in the equations are called Additional Secondary Factors (ASFs). They were calculated and placed in tables by NOAA back in the 1980s. This calculation was not a measurement, but an estimate, so there is only about 250 ft of accuracy in the tables. However, once you know a few points where you have both the loran and GPS numbers, then you can calculate the ASFs accurately and get much better conversions. This can be done manually with simple program such as POSAID or automatically with a more complex program.
    Using this technique, I provide the following conversions for your data after calibrating on the three points you supplied data for. The accuracy of the correction factors for points 4 to 6 will not be as good as for 1 to 3 as they are 20 miles away from the calibration data.

    12939.8,47015,"29-58.652","87-43.709"," ","spot #1 "
    12939.5,47010.2,"29-57.680","87-43.652"," ","spot #2 "
    12939.7,47005.2,"29-56.675","87-43.541"," ","spot #3 "
    13131.45,47013.15,"29-58.929","87-24.523"," ","spot #4 "
    13151.22,47017.03,"29-59.735","87-22.642"," ","spot #5 "
    13171.55,46983.85,"29-53.768","87-19.730"," ","spot #6 "
    12939.8,47015,"29-58.652","87-43.714"," ","spot 7 calibration "
    12939.5,47010.2,"29-57.670","87-43.645"," ","spot 8 calibration "
    12939.7,47005.2,"29-56.674","87-43.534"," ","spot 9 calibration "

    Readings 7,8, and 9 above are the same as 1 through 3 with the Lat/Lon given. I used them for calibration. The following is a report on the accuracy of the conversions.

    Slave: 7980W Mean ASF: 0.11, Variance: 0.054
    Slave: 7980Y Mean ASF: 0.13, Variance: 0.025
    The calibration readings are used to judge the accuracy of the calibration and subsequent conversions. Each calibration reading is converted to Lat/Lon using only the TDs, The calculated Lat/Lons are compared to the actual numbers. A miss distance is found for each reading and the miss distances are averaged. Next, since the conversion can be run in either direction, the loran numbers are calculated from the Lat/Lons for each reading and compared to the actual loran numbers. The following are the individual miss distances and TD errors. By the way, the results here are somewhat better than I usually see.


    Distance Error TD1 error TD2 error reading #
    26 ft. 0.05 0.00 7
    71 ft. -0.06 0.05 8
    35 ft. -0.07 0.01 9

    Average distance error: 44 ft.
    Peak Distance Error: 71 ft.
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    THanks Steve, I forgot you were up on loran conversions. I'll send you a PM.

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    Dave... what... you think you are gonna get some new numbers or something?
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    here's a helpful hint.
    Spend a couple hundred bucks and buy a loran.
    Everyone I know has some "program" to convert numbers that will get you "pretty close".
    I have an old sitex loran that I put the numbers in, it takes me to the spot; I mark it with my gps and that's it!
    Just my two cents but its pretty basic and it works.

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    Quote Originally Posted by liberty hound View Post
    here's a helpful hint.
    Spend a couple hundred bucks and buy a loran.
    Everyone I know has some "program" to convert numbers that will get you "pretty close".
    I have an old sitex loran that I put the numbers in, it takes me to the spot; I mark it with my gps and that's it!
    Just my two cents but its pretty basic and it works.

    No offense, Al, but it sounds like "everyone you know" doesn't really know the conversion processes that well. As I have told many people on forums before, its not some out of the box, plug and chug program. You have to use it correctly, which includes collecting a calibration data set. While I agree your method is the all time, 'tried and true' method, it will not help the average joe with just an interest in a handful of loran numbers. Nor will it protect your unconverted numbers in case loran takes a crap. Truth is, I can get my Sebastian area conversions within 100 feet 100% of the time, and if someone cannot find a reef let alone a wreck the size of a shopping cart within 100 feet, its time to go back to seamanship 101.

    You can choose to be in the old school of doubters with your $100 loran and book of thousands of unconverted numbers. If and when loran shuts down, or your loran takes a dump and you're stuck with that notebook of numbers you didn't get a chance to convert, you can call me and I'll show you how to do it.
    Last edited by inletsurf; 05-02-2008 at 10:24 AM.
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