Gps waypoint
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Gps waypoint
What position formats are pilots using?
dd.dddd ddd mmm.mmm dd mm ss.s
There seems to be no common standard in various publications
Flydemon uses ddd mm ss
Caa chats use ddd.dddd
Any comments please.
dd.dddd ddd mmm.mmm dd mm ss.s
There seems to be no common standard in various publications
Flydemon uses ddd mm ss
Caa chats use ddd.dddd
Any comments please.
Avoid imitations
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I think that was sung by Boney M in 1972. 
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The short answer is to avoid lat/long waypoints like the plague. So easy to get one digit wrong...
Use named waypoints e.g. VORs, airway intersections, etc if at all possible.
Use named waypoints e.g. VORs, airway intersections, etc if at all possible.
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The short answer is to avoid lat/long waypoints like the plague. So easy to get one digit wrong...
Use the format specified by the manufacturer of your GPS, ideally using a program that allows you to input the data on a computer and then transfer them to your device (minimizes input errors). Always check paper chart against GPS map to verify the WP is at the correct location.
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Most of the waypoints I've encountered were dd mm.mmm but I've seen all other variants too. Including the various national grids - although I need to admit that was not in aviation.
Need to be careful inputting them, but you also need to be careful in selecting the right datum. WGS84 seems to be standard these days in aviation, but just two weeks ago I had a major gaffe with some Italian charts that were in some datum dating back to the 1950s. As it turns out, between WGS84 and that 1950s datum there was a half-mile difference. Not really significant when flying, but very significant when you're hauling 30kgs of luggage on your back (half of which was water).
Need to be careful inputting them, but you also need to be careful in selecting the right datum. WGS84 seems to be standard these days in aviation, but just two weeks ago I had a major gaffe with some Italian charts that were in some datum dating back to the 1950s. As it turns out, between WGS84 and that 1950s datum there was a half-mile difference. Not really significant when flying, but very significant when you're hauling 30kgs of luggage on your back (half of which was water).
My homebrew GPS uses ddd.dddddd internally, for feeding data into it I type it in a spreadsheet as dd mm ss for the simple reason that I'm an old-fashioned person. Spreadsheets are great for converting data between different formats or units.
The format dd mm.mmmm seems to be a standard, used in several countries' AIP's. To me it looks like a particularly unhappy compromise between dd mm ss (traditional, and quite natural to use if one gets indeed used to it) and dd.dddddd (by far the most logical). But to be really logical, there should be 100 degrees rather than 90.
NB before talking of ss.s, first consider the distance one second corresponds to (30 yards or so, on a great circle?). I cannot imagine a single reason a pilot should ever need to go into the decimals.
The format dd mm.mmmm seems to be a standard, used in several countries' AIP's. To me it looks like a particularly unhappy compromise between dd mm ss (traditional, and quite natural to use if one gets indeed used to it) and dd.dddddd (by far the most logical). But to be really logical, there should be 100 degrees rather than 90.
NB before talking of ss.s, first consider the distance one second corresponds to (30 yards or so, on a great circle?). I cannot imagine a single reason a pilot should ever need to go into the decimals.
Last edited by Jan Olieslagers; 4th Sep 2011 at 02:01.
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Many thanks everyone for you thoughts.
My worry is that not everyone is aware of the various formats that positions are published in.
The Garmin gps menu allow setting different formats in the start menu.
My preference is ddd.mmm,ss.
Be careful if you download, ensure that the gps in in the correct format to receive the info
My worry is that not everyone is aware of the various formats that positions are published in.
The Garmin gps menu allow setting different formats in the start menu.
My preference is ddd.mmm,ss.
Be careful if you download, ensure that the gps in in the correct format to receive the info
For may years we were happy to give positions to one minute of arc i.e. 1 nm. Very occasionally there was a requirement to refine it further e.g. bomb aiming, surveying etc. Surveyors and those with a need to use Norie's Tables have always used seconds of arc giving a resolution of 100yds and beyond. Aviators have generally used decimal parts of a minute, giving an initial accuracy of 600 yds to one place of decimal, or 60 yds to two places. Early GPS ramp charts included a Lat Long overlay with a decimal grid, it was easy to use but was originally only intended to give a refined position for the alignment of Inertial Navigation Platforms whose long term accuracy depended upon it.
dd mm.m is sufficiently accurate for most aviation functions, the introduction of seconds is both unnecessary, and as you have pointed out the source of confusion, and good material to keep Murphy's Law in business. I am always fascinated that pilots are obsessed with levels of waypoint accuracy that exceed the average flying ability by factors greater than 100, meantime their watches are probably not set to within 2 minutes. Nobody ever expects to be told the time to an accuracy of greater than a minute, and time remains the keystone in navigation.
dd mm.m is sufficiently accurate for most aviation functions, the introduction of seconds is both unnecessary, and as you have pointed out the source of confusion, and good material to keep Murphy's Law in business. I am always fascinated that pilots are obsessed with levels of waypoint accuracy that exceed the average flying ability by factors greater than 100, meantime their watches are probably not set to within 2 minutes. Nobody ever expects to be told the time to an accuracy of greater than a minute, and time remains the keystone in navigation.
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Entering waypoints is best done graphically using software like Skydemon or Memory Map.
If anyone knows please let us know.
Last edited by Robin400; 5th Sep 2011 at 12:46.
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SkyDemon can use Degrees / Minutes / Seconds or Degrees / Decimal Minutes.
It's in the 'Change Units' menu. I'm pretty sure you can choose in Memory Map as well.
It's in the 'Change Units' menu. I'm pretty sure you can choose in Memory Map as well.
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In our GPS systems (nothing to do with aviation), we always try to use Degrees and decimal degrees.
The reason is that, after careful consideration, we felt that this format was the least likely to be misunderstood by a human, and the easiest to parse / process by a machine. Plus, it seems in our experience to be the most commonly accepted format (not always the most commonly presented / default setting though).
The reason is that, after careful consideration, we felt that this format was the least likely to be misunderstood by a human, and the easiest to parse / process by a machine. Plus, it seems in our experience to be the most commonly accepted format (not always the most commonly presented / default setting though).
