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-I- MARNAV About Marnav-In the early 1980's, when LORAN A was taken out of service, many mariners needed a way to convert LORAN A data to the new LORAN C delays. To meet this need, MARNAV was written by C & E Associates to run on the TRS 80 series of computers. In addition, early LORAN C receivers did not present data in a Latitude/Longitude format. Marine navigation from one point to another was rather difficult since, unlike geographic coordinates, LORAN coordinates are hyperbolic position lines. Most LORAN C users wanted their data in geographic format to simplify their navigation. This was especially true when the LORAN system was out of service for one reason or another. After several years, LORAN became available for use in aircraft. At that time, only the users manual furnished LORAN data for airports and not for all of them. It was easy to get latitude/longitude data for other airfields and navigation waypoints so Marnav was being used in the aviation community to make such data available. In the early nineties, the Global Positioning System (GPS) started to replace LORAN C. Equipment became much more reasonable in price and more and more mariners and fishermen were installing the new, more accurate, equipment. We now had a new problem; Most LORAN C users had large amounts of data in LORAN C format and now needed to change that data back to GPS format. In the meanwhile, Marnav had been upgraded several times to run on IBM compatible PC's. Even though it is a goal of any programmer to make his programs easy to use, the entire field of navigation, LORAN, GPS, etc. is technically very complicated. and writing user friendly software becomes doubly difficult. In Version 4.5, we have tried to make program operation more understandable. Most screens now include help blocks on the screen and in some cases the user is guided through especially difficult material. The menus have been changed to pull-down menus and many of the operations are called directly from the main menu. There is no difference in the shareware and the registered version of Marnav. The shareware version is shipped with the West Coast LORAN C chain so the user may try all program features to make sure the program does what needs doing. The data for other chains may be entered from data available in any LORAN instruction book, or is available from the U.S. Coast, Department of Transportation at a nominal cost. The necessary routines are provided with the program to enter this data or, to add new chains which may be announced. When you register Marnav, in addition to a printed manual, you will also receive the data files for all of the LORAN chains in the world so you do not need to enter them yourself since this can be an error prone effort. The following constants were used for all algorithms in the Marnav program. The signal propagation velocity used is the propagation velocity in free space, 299,792,458 meters per second; Sea water conductivity is 5.0 mhos per meter; Angular conversion is 0.01745329251993889 radians per degree. All calcu lations and data are in double precision. Calculations necessarily assume an all water path. In addition to the LORAN C to GPS and vice versa data conversion, the program provides the ability to navigate from one position to another where either or both positions may be specified in either LORAN C or GPS coordinates. Marnav also calculates relationships between points in terms of Speed, Time and Distance in either Nautical or Statute miles and knots or miles per hour. If the Hard Copy feature is turned ON, a hard copy record of all operations is printed as you proceed. The LORAN data bases may be created, displayed, edited and printed as required. It is possible to compensate for propagation anomalies providing position calculations accurate to several yards! Program Files-There are currently thirteen LORAN-C chains world wide. The necessary data for each chain is in contained in files named for the Group Repetition Interval (GRI). All thirteen of these files are shipped with the registered version of Marnav. In addition to these data files, one file is maintained to indicate the active chain. (The chain you are currently using). When you first bring up Marnav, it will read this active chain file and then the data for the indicated chain. It is necessary that the program and all of the data files be kept in the same directory since the program looks for the data files in whatever directory you were in when you brought up the program. The active chain is indicated on the Menu screen. -II- Marnav Menu Menu selection is relatively standard for pull down menus. Select your choice of columns using Left/Right arrows and the menu items by highlighting that item using Up or Down Arrow keys. You may also select the item by entering the letter designation for that item. Each of the menu selections will be discussed in the remainder of this documentation. -III- LORAN-C to GPS The term GPS may be unfamiliar to some LORAN users. The United States government has established a network of navigational satellites which provide extremely accurate geographic positioning. The accuracy of the basic system is so reliable that it is feared that a potential enemy could use the data to position intercontinental missiles. For this reason, there is an error transmitted which causes a positional error of several hundred feet. A number of error correction stations provide short range error correction information. These stations may be shut down in times of emergency. At any rate, this system has been called the Global Positioning System; Hence the abbreviation GPS which will be used throughout this documentation. The first item in the column labeled Data Conversion is LORAN-C to GPS. The title is self explanatory. When you choose this item, the data entry screen will be displayed with the cursor at the entry point for the first LORAN delay. Enter two delays for the location in question. If they are valid, the program will calculate the Latitude/Longitude coordinates for that location. It will then calculate the delays for any other delays in that chain. Some chains have only two secondaries, others have three or four. If you are an experienced LORAN user you know that in some parts of the service area for a given chain the signal strength and/or the orientation of the delay lines on the chart are such that certain delays are somewhat more useful than others. It is often useful to have the delays for each secondary in a chain as a matter of record for each point. The Latitude/Longitude is expressed in three formats: Degrees______________________30.2700 Degrees, Minutes_____________30 16.200 Degrees, Minutes, Seconds____30 16 12.0 The first of these is generally used on large scale charts and maps, the second is generally used on small craft charts and the last on very local geodetic survey maps. The conversion is a real nuisance when you are trying to locate a spot on map or chart. This is also a very useful feature of the program if you need to convert data from one format to another. If the data you have entered is an improper value for the normal service area of the chain you will get a message: No Useful Solution Found-Check Data More often than not, there has been a mistake in the data entry. If calculated points are a long way from the normal service area for the chain, you could not receive the loran signals anyway. In addition, if the entered delays are unreasonably far from the approximate latitude and longitude shown on the screen you may also get the same message. Calculations begin at the latitude and longitude shown as approximate coordinates. If the location of interest is a long way from them the program solution may be slow. Marnav works much faster if the approximate coordinates are within 2 degrees of the actual latitude and longitude. This is on the order of one hundred or more miles so it is rarely a problem. These values may be edited in the data base and also are automatically updated for subsequent calculations in the same area. The propagation velocity constants used by the program have been determined for free space over water. Minor anomalies occur when there is considerable land area between you and the delay transmitters. The result is that the LORAN delays for a given point today will be extremely close next time you use them to define the same point. Put another way, the repeat ability of LORAN delays is extremely high! The absolute relationship between calculated Lati- tude/Longitude and LORAN delays however may have a small error of several hundred feet in some cases. In normal navigation, this would not be a problem but there are many applications where more accurate agreement is required. Marnav allows the use of Correction Factors to offset such errors. This will be discussed later. -IV- GPS to LORAN-C This operation is opposite to that just discussed. In this case, the latitude and longitude of the point of interest is entered and all of the secondary delays for that chain are calculated. Data may be entered in any of the three formats discussed above. Enter the data in any format and it will be converted to the other two as well. For example, if you enter 30/16.2 it will be converted to the three forms shown above. The delimiter between degrees and minutes shown could have been a space, a comma or, as shown a forward slash. You should be aware that just because Marnav indicates that a delay should have a certain value, is no assurance that the signal strength of that delay will be great enough to be useful. If the LORAN is able to lock on the secondary, you will be able to use it, otherwise you will have to use one of the others. In general, the part of the service area you are in will generally determine the secondaries you should use. There are also times when the equipment for one of the secondaries has been shut down for service. Those are the times when having all of the secondaries listed is most useful. Anyone using LORAN should be aware that for any two delays there are geographically two intersections. The mathematical reason for this is that these delay lines are hyperbolas and as such will intersect twice. This may seem to be a drawback to the use of LORAN, but in general, these intersections are widely separated and if the approximate latitudes and longitudes shown on the screen are within a few hundred miles, the LORAN and Marnav will solve for the right one. At any rate, the coordinates of the wrong one would be so far away that one could not readily mistake them. When latitude is used in geographic calculations, North latitude is normally taken as a positive value. For Longitude, West latitude is normally a negative value. Since Marnav is usually used in the same earth quadrant it lets you choose which quadrant of latitude and of longitude is to be considered positive. If you are using Marnav in the continental United States it is easier to define North Latitude and West Longitude as positive quantities instead of remembering to put the minus sign in front of the longitude entries. The quadrants you choose as positive are shown on the screen and may be changed by editing the data base -V- Bearing & Distance This menu choice invokes the bearing and distance navigation routines. The coordinates for either or both of the two points may be entered in either LORAN or geographic coordinates. Note that LORAN coordinates must all be expressed for the active chain and both points must be defined in the same chain. If both points are defined by GPS coordinates, the chain does not enter into the calculation. It follows then that coordinates defined by LORAN delays must be in the active chain but the other point may be defined geographically (GPS) and may be outside of the service area for that chain! Initially the cursor will be positioned for a LORAN delay input; Simply press <Enter> and the cursor will move to the geographic input position. The second position is entered in the same way and the results of the calculation are displayed near the bottom of the screen as rhumb line heading and distance to and from the two points entered. All the same comments concerning data entry apply as they are discussed in earlier sections of this documentation. -VI- Speed/Time/Distance This menu choice provides the relationship between the distance from one point to another, the speed of the vehicle and the time of travel. Data entrance is extremely simple, if you enter any two of these quantities the program will calculate the value for the third. If the quantities entered are speed and distance, the time will be calculated and the time is presented in decimal hours as well as hours and decimal minutes. If the distance is entered in Nautical Miles, the speed will be calculated, or, must be entered in Knots. Conversely, if the speed is entered in Statute miles then the speed will be calculated, or, must be entered as Miles per Hour. Obviously, it is also true that if the speed is entered in Knots, then the distance is calculated, or, must be entered in Nautical Miles and vice versa. If time is one of the quantities being entered, the same formats as discussed previously for degrees and minutes may be used. For example, 3.75 hours and 3/45 ( 3 hours & 45 Minutes ) will produce the same result. -VII- Display Data This item, and the next four deal with the data base which defines the characteristics of the LORAN chain in use. Selecting Display Data will present the data for the chain in use. In addition to displaying the data on the screen, you may change the active chain and also make a hard copy of the data for this chain. The data displayed consists of an accurate position in terms of Latitude and Longitude of the Master for this chain as well as each of the Secondaries. As mentioned earlier, some chains have only two secondaries while others have three or four. Each secondary transmits its signal after a precise display after the master and this delay is shown along with the positional data for the secondary. Correction factors to compensate for propagation anomalies are also shown. These are discussed in detail in a separate section. In addition, the GRI number is shown. This is more than an arbitrary number since it defines the Group Repetition Interval which defines the signals for this chain. Obviously these positions and delays must be extremely accurate or the system is useless! Also shown are the Quadrants in which Latitude and Longitude are arbitrarily defined as positive values. The approximate latitude and longitude used by the program as initial points for calculation are also shown. -VIII- Edit Data Base Any of the items discussed above may be edited using this menu selection. It is strongly suggested that only approximate latitude, longitude, the positive quadrants and correction factors be edited without extremely good reason and then, only after backups of the data are saved. The Edit sequence is started by selecting EDIT DATA from the on screen menu bar. You may step through the data field by using <Enter>, <up-arrow> or <down-arrow>. Data corrections are made in the usual way. When you have finished with your edits, press <End> to return to the on screen menu. Changes made when editing this data base are recorded to disk only when you select WRITE FILE and press <Enter>. Without leaving the Edit function, you may change the Active GRI or make a hard copy of the data on the screen. -IX- Initial GRI The initial GRI is that chain which is active when you start the program. Most users do not normally change the active GRI very often but, at times, changing the location of your activities makes it necessary to do so. Simply select Initial GRI from the menu. This will change not only the GRI which is active when you start the program but will also change the GRI which you are currently using. As mentioned previously, it is also possible to make this change in the Display and Edit modes. -X- Correction Factors LORAN Calculations and their accuracy depend on the propagation velocity of radio waves. Unfortu- nately, the propagation velocity is not exactly the same over all types of terrain so the delay time to a given point may be very slightly different than it is to another point which is the same distance from the station. While these differences are extremely small, the difference can lead to errors of several hundred yards when the path from the station to your position crosses large land masses. If your concerns are simply with getting to the same spot as you were at some previous time, then this error will not concern you since the repeatability of the LORAN data for that spot is extremely good. The problems occur when you have the GPS position for a given spot and you want to convert to LORAN coordinates, or, in the opposite case, when you want to convert your LORAN data to GPS coordinates. In most cases, boaters and fisherman operate in relatively small areas often as small as ten miles or so on a side. Unless there are large geographic differences near the area, the propagation errors will probably be fairly consistent throughout the area. In that case, you may add a correction factor to your data base which will compensate for these propagation anomalies. In Marnav 4.5 the correction factor routine has been written to evaluate and enter this data quickly and easily. In order to provide the necessary data to evaluate these errors, you will need accurate data for a point in or near the area of interest. Accurate geo- graphic data is available from a number of sources. Newer marine charts have accurate positions for buoys and markers or, you can get accurate geographic data from a GPS receiver which has a correction receiver to compensate for the error intentionally put into the GPS data as transmitted from the satellites. You may also get accurate data from Geodetic survey maps in which positions along the shore are described using survey data. The data must be for a place where you can locate your LORAN to get LORAN delays for that spot. You should try to get data for all of the secondaries in the chain. In many spots this will not be possible because some secondaries will have very weak signals but try to get as many as you can. To enter correction factors into your data base, select Correct. Factors from the menu and follow the Onscreen instructions. The factors will be automatically calculated and entered into the data base. From then on, they are automatically included in the calculations and, unless you move to an area far from where they were determined, you no longer need concern yourself about them. -XI- Adding A Loran Chain It is unlikely that any new LORAN chains will be constructed since the LORAN system will gradually be phased out as more and more users get and use GPS equipment but you may wish to add data for chains not in your files. The U.S. Coast Guard makes available the exact geographic location of the Master and each of the secondaries as well as the transmission delays for each of the secondaries. Enter these data very carefully using as many decimal places as are made available. When all the data has been entered, select the Write File sub-menu option on the data screen and a file called GRIxxxx.LRN will be created where the xxxx are the numbers which define the Group repetition rate which will be defined along with the other Coast Guard data. -XII- Hard Copy The Hard Copy choice on the menu will toggle the Hard Copy switch Off and On. When On, each calculation is automatically printed on your system printer for later reference. This feature is especially valuable when cruise planning or calculating your navigation data before starting your journey. The GRI data bases may also be printed but that printing is done when you select the PRINT DATA choice from the on-screen menu during the data operations. Shareware C & E Associates has chosen to use the Shareware concept to distribute this program. This is good for us in that it contains many of the costs associated with a retail sales effort. It is good for you since it allows you to make an intelligent buying decision by trying the program to make sure it does what you want before you spend your money. It does however bring with it a legal and moral commitment to buy (Register) the program after you have tried it and found it to be to your liking. The authors of Shareware receive NO money from the distribution of their efforts until you, the user, register it. If you believe the effort that goes into writing a program such as this deserves the thirty-five dollar registration fee then please register by sending your check along with the form included at the end of the documentation. No program features have been "held back" until you register the program. When you register, you will receive a copy of the latest version of the program as well as discounts on any future program upgrades. In addition, you will be kept informed about several other programs in development on related subjects. Program support will be provided to both non-registered and registered users using Compuserve Mail addressed to Edward J. Panner, (72717,1612) or by U.S.Mail addressed to Edward J. Panner at the registration address. This program is produced by a member of the Association of Shareware professionals (ASP). ASP wants to make sure that the shareware principal works for you. If you are unable to resolve a shareware related problem with a ASP member by contacting the member directly, ASP may be able to help. The ASP Ombudsman can help you resolve a dispute or problem with an ASP member, but does not provide technical support for members' products. Please write to the ASP Ombudsman at 545 Grover Road, Muskegon, MI 49442 or send a Compuserve message via Compuserve Mail to ASP Ombudsman 70007,3536. Additional information about the legalities of Shareware may be found in the appendix to this documentation.