What symbol do you use for plotting gps position on chart?

davierobb

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I've had a look around the internet and several sailing books and can only find the symbols for plotting a gps waypoint, large + with square. Is there any standard symbol in use for plotting a gps position on a paper chart ? I'm guessing a plus over a circle might be correct but not sure why.
 

kcrane

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Funnily enough that's what I use and I know what it means to me on my charts (I write time next to it) so I stick to it, but no doubt it isn't a recognised thing, it just felt right /forums/images/graemlins/smile.gif
 
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Just as a '3-star astro fix' is derived from three Range Lines Of Position from the sub-points of stars, so a GPS fix is derived from 3 ( or more ) Range LOPs from 3 ( or more ) satellites. Some pro navigators would encourage the standardisation of plotting symbols for 'observed positions' thus:

A 'pinpoint' fix shown by a dot surrounded by a neat circle, with the time of observation alongside.

An 'observed' fix, constructed of 2 or more visual or electronic LOPs, shown by a cross surrounded by a neat circle, with the time of observation alongside.

A 'derived' fix, constructed from the output of a DR, inertial, or other navigational computer, shown by a cross surrounded by a neat square, with the time of observation alongside.

Many would consider that a GPS fix is one of the latter, and would use a box and cross on a marine chart, to differentiate from visual fixes. Others would point to an 'offset from a GPS waypoint' fix, and prefer a neat circle around a cross.

What matters is accuracy, consistency of practice and avoidance of ambiguity.

/forums/images/graemlins/ooo.gif
 

landaftaf

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I agree, a cross with a circle on it denotes an electronic position - but any fix should have a time on it for it to mean anything, and, in the best tradition of chartwork, for a gps fix it should have (gps) next to the time to identify it /forums/images/graemlins/cool.gif
 

Allan

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I can't remember if I was taught the circle and cross or if it is just "the way I have always done it" but that is my way.
Allan
 
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Skyva_2

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The RYA YM course book gives any fix, visual or GPS as a dot with circle; ideally with time and log reading alongside.
 

st599

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[ QUOTE ]
Is it a fix as its derived from a single source of data?

[/ QUOTE ]

If it was single source, you would only know you were somewhere on the edge of a sphere on space - you need at least 4 to get a position.
 

Oen

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Bil is spot on with the technical stuff - but a practical approach which some may find helpful is to consider the following:

A fix from observation (by eye), such as passing very close to a buoy, may be shown as a dot with a circle around it (the circle is round, like the eye).

A fix from position lines or transferred position lines may be shown simply by the intersection of those lines.

A fix from GPS or another electronic aid may be shown as a dot with a box around it, because it comes from an electronic 'box'.

Non-professionals (that is, those without Bil's considerable expertise in these matters) might find this scheme easier to remember...

Needless to say, all should be accompanied by a note of the time, next to the fix.
 
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