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Oregon 750t Position format


mty55

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Select a position format

  • hddd.ddddd°
  • hddd°mm.mmm'
  • hddd°mm'ss.s"
  • UTM UPS
  • User Grid
  • (others)
  • These are the position format setting listed on GPSrChive for the 7XX  series. hddd° mm.mmm. I go to to the position format on my 750t The closest format is
  • hddd° mm.mmmm'.  No option for hddd° mm.mmm'.  Both my 600 an 650 both have the proper format.
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6 hours ago, The Jester said:

Just use the hdd mm.mmmm format.  It's only adding one more decimal place.  Round the last digit down  when it's 1-4, round up if it's 5-9.

Thanks I guess its part of the learning curve going from a 650 to a 750

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2 hours ago, The Jester said:

When I got my new 66s I had to get used to an extra decimal place also.  I guess the new units are more accurate???  At least, they report on a finer grid.

No, and for this technology, anything past the third decimal place in minutes is just silly.  Makes about as much sense as dd.dddddd

1 minute of latitude is about 6068 feet.  So...

 

0.001 minutes of latitude (N/S) equates to about 6 feet.  You'd be lucky to get that kind of EPE on a good day. 

But 0.0001?  1/10 of 6 feet?   7 inches?  Caching wouldn't be very challenging if we were there.

 

0.0001 minutes of longitude (E/W) is just as silly as using it for latitude at the equator, and gets even sillier as you go north or south from there since each 0.0001 gets smaller and smaller.

 

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2 hours ago, The Jester said:

When I got my new 66s I had to get used to an extra decimal place also.  I guess the new units are more accurate???  At least, they report on a finer grid.

 

2 hours ago, The Jester said:

When I got my new 66s I had to get used to an extra decimal place also.  I guess the new units are more accurate???  At least, they report on a finer grid.

How do you like the 66s. I had and Oregon 300 and 650 both power buttons wore out. I repaired them and they work but I found a great price on the 750t.To be honest I'm less than thrilled with the interface. The last couple caching outings it was cold . Wish I would have went for the 66s. a glove friendly gps 

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52 minutes ago, ecanderson said:

No, and for this technology, anything past the third decimal place in minutes is just silly.  Makes about as much sense as dd.dddddd

1 minute of latitude is about 6068 feet.  So...

 

0.001 minutes of latitude (N/S) equates to about 6 feet.  You'd be lucky to get that kind of EPE on a good day. 

But 0.0001?  1/10 of 6 feet?   7 inches?  Caching wouldn't be very challenging if we were there.

 

0.0001 minutes of longitude (E/W) is just as silly as using it for latitude at the equator, and gets even sillier as you go north or south from there since each 0.0001 gets smaller and smaller.

 

 

I suspect centimeter level positioning precision will be available using consumer grade equipment sooner than you may think.

 

 

Edited by Atlas Cached
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1 hour ago, ecanderson said:

No, and for this technology, anything past the third decimal place in minutes is just silly.  Makes about as much sense as dd.dddddd

1 minute of latitude is about 6068 feet.  So...

 

0.001 minutes of latitude (N/S) equates to about 6 feet.  You'd be lucky to get that kind of EPE on a good day. 

But 0.0001?  1/10 of 6 feet?   7 inches?  Caching wouldn't be very challenging if we were there.

 

0.0001 minutes of longitude (E/W) is just as silly as using it for latitude at the equator, and gets even sillier as you go north or south from there since each 0.0001 gets smaller and smaller.

 

My feelings are the same, hence the multiple question marks.  Around here it's 6' N/S & about 4.5' E/W.  

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2 hours ago, mty55 said:

 

How do you like the 66s. I had and Oregon 300 and 650 both power buttons wore out. I repaired them and they work but I found a great price on the 750t.To be honest I'm less than thrilled with the interface. The last couple caching outings it was cold . Wish I would have went for the 66s. a glove friendly gps 

I've had a 60csx, 62s, 64s and now the 66s.  I've mostly liked them all, but there are minor changes that you must get used to.  The biggest surprise with the 66 was that it come set to auto log finds when it gets a wifi signal.  I'd come home, loaded finds to GASK and had it tell me there was already a log on those caches!?!  I soon found where to turn that off.  I do like the ability to download cache data live, I've used it a couple of times when I took off and realized I'd not loaded that new cache.  I'll use that more when we can start traveling in our trailer again ("gee, does this rest stop have any caches?").

 

Like you, I've had the rubber around the power buttons wear out (must be my sweat, the wife doesn't have that problem) but with the 66 they moved that switch to the top of the unit so I might not have that issue again.

 

I don't know if my unit, but I can't use ANT to send cache data to my wife's 64, but can receive it.  I think I've sent other data (waypoints) but never caches.

 

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On 2/4/2021 at 6:34 PM, Atlas Cached said:

 

I suspect centimeter level positioning precision will be available using consumer grade equipment sooner than you may think.

 

 

We've been talking about L5 here in the forum for a while, and are looking forward to GPSIII satellites in the future as well.  L5 should help to resolve some of the issues that degrade positioning performance.  GPSIII will mean that we no longer need to depend upon ground based references like WAAS and EGNOS, which will be nice as well.  And more birds in the sky has already improved ephemeris issues and the occasional lousy HDOP that we used to encounter for a couple of hours on particular days when the constellation was a bit whacked relative to our ground position.

 

But there will still  be challenges to getting the level of precision described in that talk in anything but ideal conditions.  Multipath issues, which I think will likely be improved by L5, will always remain a bugaboo that has to be dealt with in software to some lesser or greater benefit.  Quickly sorting whether a signal is direct or reflected is certainly something that continues to perplex some GPSr manufacturers now.  S/N ratios will remain an ongoing technical challenge as well.  Again, not an issue under ideal open sky conditions, but we don't always cache in an ideal environment. 

 

Heck, I don't even know if Garmin's clocks (or any others in consumer goods) are tight enough to resolve the levels that this guy is talking about (0.63m?)  Would be interesting to know whether the GPSr chip manufacturers are going to have to improve their own specs to take advantage of this, and how difficult or costly it might be.  They may be there now, or it could pose a hurdle.  No way to know from where most of us sit.

 

As an aside:  Good on them for finally preparing to dump NAD83 in favor of a more realistic model.  Long overdue.

 

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On 2/4/2021 at 7:54 PM, The Jester said:

My feelings are the same, hence the multiple question marks.  Around here it's 6' N/S & about 4.5' E/W.  

Indeed.  Irrespective of the future enhancements to the system in the sky, current models aren't seeing numbers resolved to 0.0001 provide any benefit to the person staring at the screen.  I just call it wishful thinking.

 

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3 hours ago, ecanderson said:

Multipath issues, which I think will likely be improved by L5, will always remain a bugaboo that has to be dealt with in software to some lesser or greater benefit.  Quickly sorting whether a signal is direct or reflected is certainly something that continues to perplex some GPSr manufacturers now. 

 

I don't know why.

 

Since all signals travel at the same speed (speed of light), when you receive an L1 and L5 signal from the same satellite, the one that arrived later is the 'reflected' or 'multi-path' signal.

 

I do not know if the current software in my Garmin GPSr simply throws out only the reflected signal, or if it disregards both signals from any satellite with at least one reflected signal. It probably depends on how many additional signals it is receiving that do not have 'reflection' or 'multi-path' issues. With Multi-GNSS allowing the device to use GPS, GLONASS and Galileo simultaneously, I suspect there will likely be additional signals that better serve the purpose of position calculation. Especially because both GPS and Galileo transmit Dual-Band (L1+L5/E1+E5a) signals.

 

My GPSMAP 66sr is rock solid. I just leave the tracking on all the time, and even after a full day of walking around a local zoo, both outside and inside structures (some full of concrete and water), I have virtually zero 'spider-webbing' or any other track errors to clean up. 

 

 

 

66sr WWZ 5 Miles 8 Hours No Cleanup.png

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2 hours ago, Atlas Cached said:

 

I don't know why.

 

Since all signals travel at the same speed (speed of light), when you receive an L1 and L5 signal from the same satellite, the one that arrived later is the 'reflected' or 'multi-path' signal.

 

Wrong scenario.  It's when only the reflected signal is available at decent S/N that things start to go south.  We're not talking about differentiation of the same signal with different time domains (and of course, that happens, too), we're talking about situations where the receiver is seeing only reflected signals in the wrong time domain because the line of sight signal is obscured.  Receiver doesn't know that the signal it is receiving is the reflected (delayed) version.  Common in urban canyons.

 

It's still more than I can quite follow as to how L5 is expected to mitigate these issues, but that's the word going around.

 

 

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My Samsung S20 has been indicating the presence of L5 signals, too, but don't know if the health status issue was still a factor in whether they were being used for position calculation.

Your chart only indicates that the 2F and 3 satellites are in operation, and they are all 'multi-banders', so will look like that whether L5 is actually functional yet or not.  It doesn't say specifically what the L5 messaging is at present.  Haven't seen a peep out of the govt as to the current L5 status in a while.  It had been 'Pre-operational' for eons.  Search didn't turn up any new information, either.  Even the govt page still shows 'Pre-operational' and "Unhealthy", but the page hasn't been updated since August 2020.  https://www.gps.gov/systems/gps/modernization/civilsignals/

 

 

 

Edited by ecanderson
can't bloody type
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3 hours ago, Atlas Cached said:

Since all signals travel at the same speed (speed of light), when you receive an L1 and L5 signal from the same satellite, the one that arrived later is the 'reflected' or 'multi-path' signal.

I guess I don't understand the differences between the L1 and L5 signals, but if they are coming from the same satellite at the same time, wouldn't they both reflect?

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Yes.

 

But they are transmitted over different frequencies and at differing power levels.

 

I don't have any scientific data to present (yet), but my understanding is that they are able to compare one against the other to filter out errors caused by multi-path and atmospheric interference.

 

I do not yet fully understand how the 'magic' happens, so I am still researching this subject...

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On 2/6/2021 at 6:11 PM, Mineral2 said:

I guess I don't understand the differences between the L1 and L5 signals, but if they are coming from the same satellite at the same time, wouldn't they both reflect?

 

Radio waves only travel at the same speed (speed of light) in a vacuum but are slowed when traveling through the atmosphere.  The two signals, L1 and L5, use different frequencies and are affected differently by the atmosphere that results in different travel times.  That difference can be used to correct for atmospheric induced errors to improve timing accuracy.

 

Here’s an analogy.  Suppose you have a steel rod that is exactly twenty feet long and you want to accurately measure your backyard, but in the cool morning it is one length and longer in the hot afternoon.  It also changes length even if a cloud drifts overhead.  To overcome this problem you place a brass rod right next to the steel rod with one end of both rods affixed to each other. The brass rod is one inch shorter than the steel rod. Now they both heat and cool together and the difference in length at the one inch cut is proportional to the entire length so the true length of the steel rod can be determined regardless of temperature.
  • Upvote 1
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38 minutes ago, Capt. Bob said:

Radio waves only travel at the same speed (speed of light) in a vacuum but are slowed when traveling through the atmosphere.  The two signals, L1 and L5, use different frequencies and are affected differently by the atmosphere that results in different travel times.  That difference can be used to correct for atmospheric induced errors to improve timing accuracy.

 

 

Here’s an analogy.  Suppose you have a steel rod that is exactly twenty feet long and you want to accurately measure your backyard, but in the cool morning it is one length and longer in the hot afternoon.  It also changes length even if a cloud drifts overhead.  To overcome this problem you place a brass rod right next to the steel rod with one end of both rods affixed to each other. The brass rod is one inch shorter than the steel rod. Now they both heat and cool together and the difference in length at the one inch cut is proportional to the entire length so the true length of the steel rod can be determined regardless of temperature.

I understand diffraction of wavelengths. But my understanding of multipath isn't that it's wavelength or atmosphere dependent, but rather a signal reflecting off of another object the way light reflects off of surfaces. It lengthens the path between the satellite and receiver. And in some cases, because the signal isn't broadcast as a focused beam, the same signal can hit the GPS twice if it gets received directly AND bounces off an object and hits the receiver miliseconds later. 

I just don't understand how L5 combats this in a way that L1 does not.

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@Mineral2

Or worse, you don't even get two versions (direct and delayed) of the signal, but instead, you get one delayed signal off the side of a building or canyon face (or the whatever) while the original signal is obscured (no direct line of sight to the satellite).  When in narrow confines with few satellites to work with, it can most definitely throw things off a good bit.  It's one of the reasons that 'urban canyon' caching can be such a PITA.

 

As to the earlier comments about frequency (band) vs. propagation speed, Capt. Bob has that right on the money.  That's nice for dealing with ionospheric delays which we used to depend upon WAAS and EGNOS to deal with. Truth is, the newer birds (IIR and later) are all sending on L1/L1C (1575.42 MHz) and L2/L2C (1227.6 MHz) bands, and that's where the differential time to arrive is presently being computed to deal with the atmospherics.  That was already enough frequency spread to do the computation.  The fact that L5 is just a little lower yet (1176.45 MHz) isn't necessary to that job. 

 

None of which addresses the multipath issue, or how the addition of L5 is expected to help in that regard.  The frequency difference between the two signals from the same bird won't have any significant impact on the time of arrival on the two reflected signals in the relatively tiny distance between you and that building over there.  If it were that easy, the L1/L2 difference would already be making that solution possible.  Still searching for clues here. 

 

 

 

 

 

 

 

 

Edited by ecanderson
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3 hours ago, Capt. Bob said:

Yes, that deals with cases where you can see the green, blue and purple signals, but what happens when you're in a situation (and I'd argue that their picture shows EXACTLY this problem if you think that green signal is going through a steel and reinforced concrete building - not) where the original green signal is obscured.  The green signal isn't going to pass through a skyscraper. 

 

In a true 'urban canyon', or even a real one, there are usually more reflected signals than there are direct ones since the 'slot' through which there is line-of-sight to satellites is quite narrow, running along whatever axis the street runs, and only a small number of degrees wide - and runs narrower with taller buildings.  The vast majority of the constellation is obscured from direct line-of-sight reception, and only their reflections are available.  THAT'S where it gets really messy, and is where the L1/L2 differential that normally could assist simply cannot.  I don't see how the addition of L5 changes that.  Seems to me that there's no simple solution to that.

 

That leaves us with a narrow corridor in the sky with available direct signals, which, no matter how many in the constellation happen to fall within that axis, is NOT an optimal geometry to work with for positioning accuracy.

 

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One thing in this 3 year old article was worth further mention:

"Why is this only happening now? 'Up to now there haven’t been enough L5 satellites in orbit'”

 

Between Block IIF (12) and Block III (3), they have 15 of them up now.  Under the most extreme spreads of the constellation, it is said that 24 need to be functional at any one time to provide worldwide service.  That leaves a few  to go.  Lockheed/Northrup and SpaceX need to get busy.  The schedule of record is for 3 more Block III in 2021, 2 more in 2022, and 1 more in 2023.  My math tells me we'll still be short a few L5 capable birds by the end of Block III.  Block IIIF doesn't fly until 2026.

 

Still doesn't matter until we see "Healthy" reports with real data on L5 from any of them.

 

 

 

Edited by ecanderson
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9 minutes ago, ecanderson said:

Still doesn't matter until we see "Healthy" reports with real data on L5 from any of them.

 

Maybe that will be when my GPSMAP 66sr starts showing sub meter instead of 1.8 meter accuracy? 

 

Sure works well with the system we currently have.

 

 

11 minutes ago, ecanderson said:

Between Block IIF (12) and Block III (3), they have 15 of them up now.  Under the most extreme spreads of the constellation, it is said that 24 need to be functional at any one time to provide worldwide service.  That leaves a few  to go. 

 

While their may not be 24+ GPS satellites transmitting on L5 band yet, we still get to use the older SV's as well, so not as big a deal as when the constellation was first put into service. PLUS, we also can use Galileo satellites transmitting on E5a simultaneously, so there are plenty to use already....

 

I guess it only gets better from here....

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