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Old 01-28-2010, 01:16 PM   #1
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Default GPS question

This may be a stupid question but I've had some charts that use different datums but are most numbers in WGS 84? More specificly the new nearshore reefs that were set last july?

thanks for the help in advance.:letsdrink
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Old 01-28-2010, 02:01 PM   #2
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Default RE: GPS question

dang dusty, seems like you would be the one to answer that question. i bet the new stuff is nad83 or wgs84 datum, but you rarely find the old stuff right where it is supposed to be or even some of the new stuff. i always put the public numbers in then drive around in circles till i find it, then remark it with the same name but with a + sign at the end.
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Old 01-28-2010, 02:38 PM   #3
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Default RE: GPS question

thanks Mark I just got a gps and bottom machine for my kayak and there are some nearshore reefs I wanna try. These are new numbers so your probably right, I just wish they would tell you when they publish the numbers because there can be a huge difference between different datums:banghead.
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Old 01-28-2010, 03:12 PM   #4
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Default RE: GPS question

hell yell

when you are out there you can swap your datumsback and forth on your gps. if you want to come by the house we can look though the numbers i have and see what we can find. also mbt has quite a list on their website and if you stop by their shop i think they have them plotted out on a map.
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Old 01-28-2010, 06:57 PM   #5
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Default RE: GPS question

:bump
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Old 01-29-2010, 09:29 AM   #6
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Default RE: GPS question

can someone please answer this question?
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Old 01-29-2010, 09:36 AM   #7
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Default RE: GPS question

i think you are worrying about it too much. use the default setting on your gps and im sure you will be fine for any of the new deployments.
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Old 01-29-2010, 09:47 AM   #8
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Default RE: GPS question

I really don't know and can't answer that. I just use the default setting. If you are going to be out in the kayak anyway, go to a known public number, maybe even the boat ramp or a close in public number that you know. Anchor on it and start going through the datums. Use whichever is right on.
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Old 01-29-2010, 10:06 AM   #9
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Default RE: GPS question

WGS 84 is the standard spheroid for us navigational charts and navigational instruments. However, a user can select a different spheroid for most GPS units. Using a different spheroid can result in significant (miles) of error, depending on the location. If a person publishes numbers or a company publishes a chart in other than WGS 84, they should note that (since it is non-standard in the US)

Probably more info than you need, but a spheroid is the grid a particular system lays over the earth. Different spheroids have different starting points and orientations, so they don't match up, so you get errors if you use one when you should be using another.
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Old 01-29-2010, 10:58 AM   #10
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Default RE: GPS question

In the 1980s, the United States Department of Defense used the Geodetic Reference System, 1980 (GRS 80) and Doppler satellite images to create a new, more accurate world geodetic system. This became what is known today as WGS 84. In terms of reference, WGS 84 uses what is called the "zero meridian" but because of the new measurements, it shifted 100 meters (0.062 miles) from the previously used Prime Meridian.

Similar to WGS 84 is the North American Datum 1983 (NAD 83). This is the official horizontal datum for use in the North and Central American geodetic networks. Like WGS 84, it is based on the GRS 80 ellipsoid so the two have very similar measurements. NAD 83 was also developed using satellite and remote sensing imagery and is the default datum on most GPS units today.
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