Re: Long/Lat

This WebDNA talk-list message is from

2002


It keeps the original formatting.
numero = 42565
interpreted = N
texte = >I've got that zip codes database that was posted a week or so ago but I'm >looking for something with more accurate long/lat information. That >database says 98112 is the same long/lat as 98105 when they're really 3-4 >miles apart.... >Jesse, Using lat/long isn't as simple as you might expect. Land surveyors and nautical navigators can tell you that there's a lot involved, including different theories and constants used in the calcs. Some assume the earth is a sphere. Others assume the earth is a spheroid or even flat. Some use one set of measurements for the dimensions of the earth, some use another. Each has practical applications and its assumptions are perfectly valid for them, but you can't mix one set with another and get accurate results.First, you need to know how the lats and longs were determined. Which type of projection was used to represent the surface of the earth? Cylindrical, conical, azmuthal, zenital, etc.Once you know that, you can use the correct set of formulas and tables to calc the distance and bearing between two known points.If you really want to get into the theory and real-world practice of navigation, get a copy of American Practical Navigator (aka, Bowditch). Parts of it are in pdf at . Read Chapters 2 and 24 for an idea of what you're getting into.There are bound to be nautical courses available in the Seattle area. Check the community colleges or sailing clubs to see if anyone offers a course in navigation.Your local lake sailor with a sailboat on a trailer may know a bit about this sort of thing, but you'll need a real long-distance, deep-water sailor who owns a sextant to find out the real stuff.Glenn------------------------------------------------------------- This message is sent to you because you are subscribed to the mailing list . To unsubscribe, E-mail to: To switch to the DIGEST mode, E-mail to Web Archive of this list is at: http://search.smithmicro.com/ Associated Messages, from the most recent to the oldest:

    
  1. Re: Long/Lat (Jesse Williams-Proudman 2002)
  2. Re: Long/Lat (Glenn Busbin 2002)
  3. Re: Long/Lat (Jesse Williams-Proudman 2002)
  4. Re: Long/Lat (Glenn Busbin 2002)
  5. Re: Long/Lat (and The ZipBurst CGI Pro) (David M. Dantowitz 2002)
  6. Re: Long/Lat (David M. Dantowitz 2002)
  7. Re: Long/Lat (dale 2002)
  8. Re: Long/Lat (Alain Russell 2002)
  9. Long/Lat (Jesse Williams-Proudman 2002)
>I've got that zip codes database that was posted a week or so ago but I'm >looking for something with more accurate long/lat information. That >database says 98112 is the same long/lat as 98105 when they're really 3-4 >miles apart.... >Jesse, Using lat/long isn't as simple as you might expect. Land surveyors and nautical navigators can tell you that there's a lot involved, including different theories and constants used in the calcs. Some assume the earth is a sphere. Others assume the earth is a spheroid or even flat. Some use one set of measurements for the dimensions of the earth, some use another. Each has practical applications and its assumptions are perfectly valid for them, but you can't mix one set with another and get accurate results.First, you need to know how the lats and longs were determined. Which type of projection was used to represent the surface of the earth? Cylindrical, conical, azmuthal, zenital, etc.Once you know that, you can use the correct set of formulas and tables to calc the distance and bearing between two known points.If you really want to get into the theory and real-world practice of navigation, get a copy of American Practical Navigator (aka, Bowditch). Parts of it are in pdf at . Read Chapters 2 and 24 for an idea of what you're getting into.There are bound to be nautical courses available in the Seattle area. Check the community colleges or sailing clubs to see if anyone offers a course in navigation.Your local lake sailor with a sailboat on a trailer may know a bit about this sort of thing, but you'll need a real long-distance, deep-water sailor who owns a sextant to find out the real stuff.Glenn------------------------------------------------------------- This message is sent to you because you are subscribed to the mailing list . To unsubscribe, E-mail to: To switch to the DIGEST mode, E-mail to Web Archive of this list is at: http://search.smithmicro.com/ Glenn Busbin

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