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Mercator Sailing: Course and Distance
09-03-2018, 10:10 PM (This post was last modified: 09-11-2019 12:02 AM by Gene222.)
Post: #20
RE: Mercator Sailing: Course and Distance
Thanks for your comments on the program. I definitely bit off more than I could chew with this program. The revised program is attached.

Regarding the header and footer text that can be seen when the program is viewed as text file, I had previously copied the hp program code into WordPad 6.3 for Windows 8.1. I used WordPad's find and replace to change some of the variable names. I then copied the code back into the hp prime connectivity kit program editor. I had no idea that the pasted text from WordPad included all that gobbledygook information in the header and footer of the program. Some of the information is the revision history of the find and replace operations. I do not understand what null bytes are or what this gobbledygook information really is, so I just left it in the hp prime program.

I changed the upper limit of the latitude to be 85 degrees. A latitude of 85 degrees includes all of Greenland and the antarctic seas. The Meridional Parts table 6 in Bowditch goes up to 89°59′ (MP=30351.6), but you really should not be using Mercator Sailing in the polar regions. The book Calculator Afloat says you should use a different method such as using both Rhumb-line and Great Circle sailing in tandem. Bowditch says that for the polar regions, you should use a local conic projection map of the area or an Oblique Mercator Map where the Earth is tilted about 45 degrees so that the north pole appears in the mid-northern latitudes or some other map projection. I modified the program to print a note that this program is not for polar regions and is only for educational use. The program was designed to print out the intermediate results as if one were calculating the course and distance by hand using a Meridional Parts table.

I changed the program to check for the MeridPartDiff=0 instead of Lat1=Lat2.

I rewrote the procedure for East-West lines to check for all four cases (NE, SE, SW, and NW). The procedure seems to also work with 0 and 180 meridian crossings.

I think I got all the errors corrected, but I said that before.

Example 1. Our position is L 32°14.703′ N, λ 66°28.902′ W, and we wish to determine the course and distance to a point near Chesapeake Light, in L 36°58.703′ N, λ 75°42.201′ W, by Mercator sailing.

[Image: merc1.png] [Image: merc2.png]

Example 2 for an East-West course. Our position is a point off Port Aransas, Corpus Christi, Texas at L 27°50.1′ N, λ 97°0.5′ W, determine the course and distance to a point north of Tampa Bay, Florida at L 27°50.1′ N, λ 82°58.1′ W.

[Image: merc3.png] [Image: merc4.png]

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RE: Mercator Sailing: Course and Distance - Gene222 - 09-03-2018 10:10 PM

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