Hello all, I have a small problem that has me confused. I use a handheld megellan and also a laptop gps to obtain my position when sailing. Ive just noticed that the two have the same reading except for the seconds . One will read N39'52.20", while the other reads N39'52.33. I understand this is a small amount, but will it set me off by a lot or just a few feet? Right now the handheld is side by side with the gps receiver of the laptop. I would have thought that they would have been pretty much the same. Any help/advice would be helpful. Thanks
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I am no navigator but, I do know you can have either "normal" 60 seconds in a min or decimal 100 decimal seconds in a min display.
so 33 decimal seconds is 1/3 of a min or 20 normal min your GPS units are in agreement. If you have a chart plotter you don't need to worry about it, if you have DSC you don't need to worry about it cause the human is out of the equation. If you need to manually figure out where you are you need to be aware of this potential for confusion.
Why oh why did they do this?
so 33 decimal seconds is 1/3 of a min or 20 normal min your GPS units are in agreement. If you have a chart plotter you don't need to worry about it, if you have DSC you don't need to worry about it cause the human is out of the equation. If you need to manually figure out where you are you need to be aware of this potential for confusion.
Why oh why did they do this?
I second John's advice. Make sure they are both set the same, i.e. degrees/minutes/seconds or degrees/minutes and decimal of minutes. If they still don't agree, then ....
I plot manually and just noticed the difference. Since I don't have a chartplotter on board, I've gotten pretty good at it. I have a sextent but suck at that.
This was the first time that the two of them were on together. Thanks
This was the first time that the two of them were on together. ThanksThe 0.13 Seconds difference in Lat. translate to a 13.2 FEET difference. Not an issue. But, I agree with others to make sure that the DATUM setting in both devices is set to the same Datum (i.e. WS84, etc.).
I would discard decimal seconds completely. The accuracy of commercial GPS is not the same as military GPS. The question is do you really need to know right down to 3 feet where you are located? Not really. So that is like having two watches. One will always be off.
I have five clocks in my house that use the time signal from WWVB and none of them are 100% snott on with each other. So within a few seconds are accurate enough.
I personally wouldn't get too caught up on "exact" location in terms of tenths of seconds. Minutes and seconds (in integers) should be accurate enough.
I have five clocks in my house that use the time signal from WWVB and none of them are 100% snott on with each other. So within a few seconds are accurate enough.
I personally wouldn't get too caught up on "exact" location in terms of tenths of seconds. Minutes and seconds (in integers) should be accurate enough.
There is a small error inherent in all GPS units. Check your specs, and you'll find how close the unit will come. On my Raymarine 125, the estimate is 5 meters 95% of the time, but it can be off more depending on the received signal strength.
thanks for all the input. if I am within three to fifteen feet, I should be able to eyeball the rest. thanks again for setting my concerns to rest....
Here is what Wiki has to say
http://en.wikipedia.org/wiki/Geographic_coordinate_conversion
As I recall a couple of years ago there was a rescue on Lake Mich where the Coast Guard was several miles off because of unit confusion.
http://en.wikipedia.org/wiki/Geographic_coordinate_conversion
As I recall a couple of years ago there was a rescue on Lake Mich where the Coast Guard was several miles off because of unit confusion.
Slightly off topic, but I think there is an issue with how coordinates are "spoken" on the radio. One issue I have heard while working in the satellite industry was the way the information is relayed. Too many want to say the values in tens or hundreds, not single digits.
An example:
123* 45' 35" is normally spoken one hundred twenty-three degress, forty-five minutes, thirty-five seconds.
Over the air this could be garbled and misunderstood (as was over the phone many times)
I believe the correct way would be:
One-two-three degrees, four-five minutes, three-five seconds
I am sure this is anal, but when given this format over the radio or phone, each number is understood or if needed to be repeated, then there is verification.
Just my two cents worth having been involved in this technology for many years.
An example:
123* 45' 35" is normally spoken one hundred twenty-three degress, forty-five minutes, thirty-five seconds.
Over the air this could be garbled and misunderstood (as was over the phone many times)
I believe the correct way would be:
One-two-three degrees, four-five minutes, three-five seconds
I am sure this is anal, but when given this format over the radio or phone, each number is understood or if needed to be repeated, then there is verification.
Just my two cents worth having been involved in this technology for many years.
I think you are trying to tell us your position is “North 39 degrees and 52.20 minutes” not “North 0 degrees, 39 minutes and 52.20 seconds” as some have interpreted. The difference between your two readings is 0.13 of a minute not 0.13 of a second. One minute of latitude is one nautical mile. http://en.wikipedia.org/wiki/Nautical_mile The difference between your two reported positions is actually 0.13 of a nautical mile or about 790 feet. This is a very significant value. I suspect that one of the GPS units is not working correctly or they are not looking at the same satellites. Or ????
When I was taught celestial navigation, the Norwegian sailor that did it would almost smack me on the side of the head when I would get caught up worrying about seconds. He would say, "We're not in the f****** Navy, don't sweat the seconds. So WHAT if you miss it by a couple of miles, by then you'll see it".
He sort of had a way of getting his point across..
He sort of had a way of getting his point across..
I agree with Brian but I heard the CG reply saying 26 dot 39 dot 22 when repeating a location. Over the radio it was very clear and I would assume the CG operator was familiar enough with coordinates that it was very clear to the parties involved. As is often that case I only heard the CG's side of the conversation over their jillion watt radio so I have no idea what the other party was saying.
The original post - "One will read N39'52.20", while the other reads N39'52.33."
My guess is the first is a possible misreading of 52' 20" (52 minutes 20 seconds) while the second is possibly 52.33'. (52 point 33 minutes). 0.33' is the same as 20" ( 1/3 of 1 minutes = 20 seconds) so they are actually reading exactly the same position just in a different format. The two units are not set up to read out in the same format.
Sound logical?
Sounds logical to me. Just for fun I worked out what the max difference could be.
For example if you have a reading of 38.5959 vs 38 deg 59 min 59 seconds are about 24nm apart. If you have a mixed system of 38 deg 59.59 then you are down to 1/2 nm or so.
Anyway automated stuff DSC EPRIb should work fine but if you call out your position or are trying to plot the position of somebody else you need to pay attention.
For example if you have a reading of 38.5959 vs 38 deg 59 min 59 seconds are about 24nm apart. If you have a mixed system of 38 deg 59.59 then you are down to 1/2 nm or so.
Anyway automated stuff DSC EPRIb should work fine but if you call out your position or are trying to plot the position of somebody else you need to pay attention.
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