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Now THIS is GPS accuracy!

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AI8550 STATION RECOVERY (2010)

AI8550

AI8550 RECOVERY NOTE BY SOUTH CAROLINA GEODETIC SURVEY 2010 (RPM)

AI8550 RECOVERY OF THE GEODETIC CONTROL WAS ATTEMPTED USING A DUAL

AI8550 FREQUENCY GLOBAL NAVIGATION SYSTEM (GNSS) RECEIVER. THE RECEIVER

AI8550 WAS CONNECTED TO THE SCGS VIRTUAL REFERENCE NETWORK. THE RECEIVER WAS

AI8550 USED TO NAVIGATE TO THE COORDINATES OF THE CONTROL MONUMENT.

AI8550 WHEN CONNECTED TO THE VIRTUAL REFERENCE NETWORK, THE GNSS RECEIVER

AI8550 IS CAPABLE OF CALCULATING COORDINATES WITH HORIZONTAL ACCURACIES

AI8550 OF APPROXIMATELY 0.015 METER, VRS LED TO A BROKEN CONCRETE POST,

AI8550 PRESUMED DESTROYED.

 

The SCGS staff tells me that they take continuous observations to determine correction factors, and they broadcast these in real time. Surveyors can make use of them in the field, instead of having to apply the corrections when they get back to their offices.

 

-Paul-

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They're not really that expensive, a Trimble GeoXH is less than $6000 and will do real-time 30cm with the internal antenna and 10cm with an external one.

Because everyone just has 6 grand laying around. :anibad::laughing::)

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Very interesting! Christmas and my birthday are fast approaching. I'll drop some hints to the family. :anibad:

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Very interesting! Christmas and my birthday are fast approaching. I'll drop some hints to the family. :)

Your family gives $6,000 presents?? :laughing:

 

Would they like an adopted sister? :anibad:

 

Patty

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They're not really that expensive, a Trimble GeoXH is less than $6000 and will do real-time 30cm with the internal antenna and 10cm with an external one.

Because everyone just has 6 grand laying around. :anibad::laughing::)

 

I was just saying it's cheaper than a new car, not that it's actually inexpensive. :P

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The survey-grade receiver's that are dual frequency and can hook into the virtual reference networks run in the $20,000-25,000 range per unit. These units have repeatable horizontal and vertical accuracies down to the 1-2 cm range.

 

The Trimble Geo units are single phase units with no vertical component.

 

Ask for a Trimble R8 for Christmas, that is when you know that your family truly loves you!

 

Kurt

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What do you guys know about the Lecia 300 system? I have a chance of getting one for.. I think rather cheap. I've learned to used a single-phase (L1) one from Jerry on here - whom I haven't heard from in almost a year? - and was wondering how this system was?

 

--Cheers,

Mike.

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What do you guys know about the Lecia 300 system? I have a chance of getting one for.. I think rather cheap. I've learned to used a single-phase (L1) one from Jerry on here - whom I haven't heard from in almost a year? - and was wondering how this system was?

 

--Cheers,

Mike.

 

Leica makes great equipment; we started with Leica static GPS units around 1990, but moved to Trimble around 1995 for all of our GPS units. I still prefer Leica Total Stations over Trimble's conventional units.

 

That being said, the Leica 300's are good equipment. Are you buying a set with radio; or are you simply going to use it for static processing to CORS or OPUS; or do you have some sort of reference station that can be used in your area? Do you get the Leica software and license? I do not like the Leica processing software which you would need for most data processing or transfers.

 

Kurt

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The survey-grade receiver's that are dual frequency and can hook into the virtual reference networks run in the $20,000-25,000 range per unit. These units have repeatable horizontal and vertical accuracies down to the 1-2 cm range.

 

The Trimble Geo units are single phase units with no vertical component.

 

Ask for a Trimble R8 for Christmas, that is when you know that your family truly loves you!

 

Kurt

 

While it's not in the same category as an R8, the GeoXH is a dual frequency receiver, and can connect to a VRS network.

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Leica makes great equipment; we started with Leica static GPS units around 1990, but moved to Trimble around 1995 for all of our GPS units. I still prefer Leica Total Stations over Trimble's conventional units.

 

That being said, the Leica 300's are good equipment. Are you buying a set with radio; or are you simply going to use it for static processing to CORS or OPUS; or do you have some sort of reference station that can be used in your area? Do you get the Leica software and license? I do not like the Leica processing software which you would need for most data processing or transfers.

 

Kurt

Hi Kurt - I'm assuming, looking at the terms of sale, all I would be getting is the antenna, reciever, and a battery. No radio, so if I used it, it would be static / CORS.

 

I Have the GNSS software, which JerryW had shown me how to use - if it's not compatible with that tho, the I'd just pass on it. :/

 

Thanks,

Mike.

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I've used a Leica Total Station, it was very nice.

For folks that are really looking into getting one of these - and don't want live readings to use it to FIND a station, instead of simply getting readings off of a station - check your local government surplus. My town's selling a Leicia for $50. That's why I was asking my questions. I may get it from them, I may not. Still deciding. :D

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For folks that are really looking into getting one of these - and don't want live readings to use it to FIND a station, instead of simply getting readings off of a station - check your local government surplus. My town's selling a Leicia for $50. That's why I was asking my questions. I may get it from them, I may not. Still deciding. :D

At that price! Grab it for resale if nothing else. You could destroy it playing in the woods and not be out enough to make you even tear up. Grab it by all means.

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For folks that are really looking into getting one of these - and don't want live readings to use it to FIND a station, instead of simply getting readings off of a station - check your local government surplus. My town's selling a Leicia for $50. That's why I was asking my questions. I may get it from them, I may not. Still deciding. :D

At that price! Grab it for resale if nothing else. You could destroy it playing in the woods and not be out enough to make you even tear up. Grab it by all means.

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For folks that are really looking into getting one of these - and don't want live readings to use it to FIND a station, instead of simply getting readings off of a station - check your local government surplus. My town's selling a Leicia for $50. That's why I was asking my questions. I may get it from them, I may not. Still deciding. :D

At that price! Grab it for resale if nothing else. You could destroy it playing in the woods and not be out enough to make you even tear up. Grab it by all means.

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I've used a Leica Total Station, it was very nice.

For folks that are really looking into getting one of these - and don't want live readings to use it to FIND a station, instead of simply getting readings off of a station - check your local government surplus. My town's selling a Leicia for $50. That's why I was asking my questions. I may get it from them, I may not. Still deciding. :D

 

Mike,

 

If all you would be out is $50; I would definitely go for it. I'm not sure what software Jerry has shown you to use, but all you would need to do is get the rinex files out of the Leica unit and then you can submit them to OPUS and get some great information.

 

It would be fun for you to verify horizontal control stations against the NGS record, you can check leveled bench marks against the geoid(in most cases you should be within a foot of the record), you can also have a better chance at finding unfound horizontal stations by setting a temporary point(nail) and getting an OPUS position and then going back with your inverse to pull over and probe or dig.

 

I was incorrect about the GeoXH not having L1/L2, but it still does not give an accurate vertical component and this Leica unit does have that capability. Sounds like a good buy to me.

 

For $50 you can defintely part it out and get your money back if you find out you don't have all the parts needed.

 

Good luck.

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At that price! Grab it for resale if nothing else. You could destroy it playing in the woods and not be out enough to make you even tear up. Grab it by all means.

If all you would be out is $50; I would definitely go for it. I'm not sure what software Jerry has shown you to use, but all you would need to do is get the rinex files out of the Leica unit and then you can submit them to OPUS and get some great information.

 

It would be fun for you to verify horizontal control stations against the NGS record, you can check leveled bench marks against the geoid(in most cases you should be within a foot of the record), you can also have a better chance at finding unfound horizontal stations by setting a temporary point(nail) and getting an OPUS position and then going back with your inverse to pull over and probe or dig.

 

I was incorrect about the GeoXH not having L1/L2, but it still does not give an accurate vertical component and this Leica unit does have that capability. Sounds like a good buy to me.

 

For $50 you can defintely part it out and get your money back if you find out you don't have all the parts needed.

Can the Leica units export/save/transfer Rinex files? The software Jerry showed me (and I still have installed) is something called "GNSS Solutions" - it's free from the manufacturer, and the later versions have a great feature that it will automagically grab CORS information to give you your proper readings.

 

I'll call them tomorrow and tell them I'll take it, see what they say. It's "as is", and not guaranteed to work tho, but $50 ain't that much - I've wasted more online. :D

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Yeah, for $50, jump on that. Depending on the age, it's probably worth a lot more than that. I wish I had one of my own. It's an incentive to learn to be a surveyor. :-)

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Yeah, for $50, jump on that. Depending on the age, it's probably worth a lot more than that. I wish I had one of my own. It's an incentive to learn to be a surveyor. :-)

Waiting to hear back from them now. I cam across it by accident while looking for surplus traffic control equipment (..don't ask). We'll see what they say when they get back to me. I'm actually more interested on using this on my railroad, to get some good grade measurements in..

Edited by foxtrot_xray

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Yeah, for $50, jump on that. Depending on the age, it's probably worth a lot more than that. I wish I had one of my own. It's an incentive to learn to be a surveyor. :-)

Waiting to hear back from them now. I cam across it by accident while looking for surplus traffic control equipment (..don't ask). We'll see what they say when they get back to me. I'm actually more interested on using this on my railroad, to get some good grade measurements in..

Just thought I'd mention that a good tripod to mount this thing on might cost you more. And accessories like the crystal thingies that you can use to find local objects (never an excuse anymore to miss any reference marks) have got to be pricey.

 

When all is said and done, please let us know the bottom line.

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I'm still here. First thing to worry about on a used survey grade GPS is what is included and what is not.

 

1) How is it powered. Batteries, usually special types. You need to know if they are included, what they cost to replace, and how they are recharged and what the charger would cost. Don't forget to see if there is a power cable.

 

Someimes old units have batteries that have leaked and damaging the unit. Also there are sometimes internal backup batteries that start to fail after 8-12 years.

 

2) What about the antenna. Some units have built in antennas but the norm, especially for L1/L2 units is an external antenna. These can be very expensive if you had to buy one by itself. Also the proper cable to the antenna. The cable alone can be well over $100. Dual frequency survey grade antennas are typically $500-$800 used.

 

3) Software to communicate with the thing even if you don't have processing software. There are several versions of L1 only software available free on the internet, but L1/L2 usually costs quite a bit. Of course with dual frequency you can process it with OPUS or OPUS-RS for a single station. You have to have some kind of software to even generate rinex files usually.

 

4) There are two basic types of Survey Grade GPS receivers.

 

L1 or single frequency units. These are often much less expensive and are usually used for static observations requiring 20 minutes to a number of hours set up on a station. They can be found on ebay for from $400 on up. A new one would probably be about $2500 and up.

 

L1/L2 or dual frequency units. These can be found on ebay for typically $1500 and up and new would probably be 3 times that. Almost always require a special antenna.

 

Generally dual frequency units can be configured to do RTK or real time kinematic observations, but that may depend on the specific internals of the receiver. Also it requires another set of interfaces, for a radio link to a base and thus running two receivers. So that is one thing that runs the price up for a complete setup to in the $25K to $30K area. There are new ways of doing RTK these days that use networks of base stations accessible via the internet, but that is another story.

 

All survey grade GPS units are capable of obtaining positions to less than a cm, RTK not quite as good, but static sessions down to mm's relative to whatever network you tie into horizontal. Vertical is generally about half as accurate.

 

Static survey grade GPS must be post processed with some kind of software that sorts out all the data and computes a 'vector' from one station to another. This can be two of your own or one and a CORS station. RTK computes this in the receiver and also requires some kind of controller or data collector, another part of the expense.

 

There are resource grade receivers such as the Trimble Geo-XT type units that collect data that can be downloaded and post processed to the sub meter or cm level depending on the unit.

 

There are also receivers that are so old they won't work anymore due to Y2K type issues.

 

Leaves off here in Maryland, about time to think about Maryland Heights stations again?!

 

- jerry

Edited by jwahl

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Leaves off here in Maryland, about time to think about Maryland Heights stations again?!

I hadn't thought about that: some of you live in areas with a short window between when the trees don't interfere with GPS signals and when the benchmarks are under two feet of show. :laughing:

 

Patty

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I'm still here. First thing to worry about on a used survey grade GPS is what is included and what is not.

 

1) How is it powered. Batteries, usually special types. You need to know if they are included, what they cost to replace, and how they are recharged and what the charger would cost. Don't forget to see if there is a power cable.

Jerry, good to hear from you! Was worried you fell down a rabbit hole, or I had REALLY pissed you off! :(

 

Thanks for the info, too. Spoke with them today, and supposedly the system is a SR399 antenna, with a TR399 receiver. The battery is included, but the charger is not. Cables are included, the mounting materials to connect it to a tripod are not.

 

They had one of their employees want it so he got it. :( However, there's another one for sale in the same town for $300. (It's in better condition, and comes with tripod mount and little eye spot like you had to spot down over the mark, but no charger still.) While 3 smackers may be a good price, that's pushing it for me right before the holidays. ;)

 

Been looking at Sugarloaf Mountain - I believe we had talked about that last Spring. It's looking like I may want to tackle that, if interested. :P

Edited by foxtrot_xray

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Leaves off here in Maryland, about time to think about Maryland Heights stations again?!

I hadn't thought about that: some of you live in areas with a short window between when the trees don't interfere with GPS signals and when the benchmarks are under two feet of show. :(

Patty

Since last winter was my first winter here, all I can say is - so far, it's been great. :( No snow (yet! knock on wood) and the temps haven't been freeze-your-nose-off cold. The only downside I've noticed so far is that up here (compared to where I was in Georgia), the time the sun is up in the sky and useable is very limited.

 

Went on a "power" benchmark run yesterday, up a road/rail line, able to find 14 different stations, including one that that had scaled coordinates over 1000 feet away (wrong roadbed) and a marker that previous recoveries couldn't find. Was good weather for it. ;)

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I've used a Leica Total Station, it was very nice.

 

I have used those in the mid to late nineties for doing airfied suveys.

Edited by cowpill

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They're not really that expensive, a Trimble GeoXH is less than $6000 and will do real-time 30cm with the internal antenna and 10cm with an external one.

 

30 centimeters = 11.8110236 inches

 

Our handhelds will frequently (about 1 in 5 times) put us at 24 inches or slightly less when finding adjusted marks.

 

Are you sure the 30 cm is correct?

 

John

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What handhelds are those? It's certainly not a garmin...

 

1 is a Magellan Meridian Platinum and the other is a DeLorme PN40.

 

I'll see if I can find a photo.

 

John

 

Here's a shot of 1 with the GPSr reading 2 feet to go. This one is the Meridian Gold.

 

55718140-2f0a-4428-9a18-605ec57a9474.jpg

Edited by 2oldfarts (the rockhounders)

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Did you use HTDP to convert from NAD83 to WGS84? If not, then your coordinates were already off by 1.25 meters:

 

 TRANSFORMING POSITIONS FROM NAD_83(CORS96)   (EPOCH = 01-01-1992)
					  TO WGS_84(G1150)	(EPOCH = 12-08-2007)

		 INPUT COORDINATES   OUTPUT COORDINATES	INPUT VELOCITY


 LATITUDE	 35 49 54.04858 N	 35 49 54.06516 N	  1.35 mm/yr  north
 LONGITUDE   111 26 13.35218 W	111 26 13.39761 W	  1.14 mm/yr  east
 ELLIP. HT.		   1380.500		   1379.648 m	 -1.09 mm/yr  up
 X				-1892475.274	   -1892475.973 m	  1.67 mm/yr
 Y				-4819852.924	   -4819851.586 m	  1.14 mm/yr
 Z				 3713874.250		3713874.166 m	  0.45 mm/yr

 

Ellipsoid : GRS80 / WGS84  (NAD83)		
 Equatorial axis,	a   =	6378137.0000
 Polar axis,		 b   =	6356752.3141
 Inverse flattening, 1/f =  298.25722210088

 First  Station : NAD83						 
  ---------------- 
LAT =  35 49 54.04858 North 
LON = 111 26 13.35218 West  

 Second Station : ITRF00						
  ---------------- 
LAT =  35 49 54.06516 North 
LON = 111 26 13.39761 West  

 Forward azimuth		FAZ = 294  8 25.3681 From North
 Back azimuth		   BAZ = 114  8 25.3415 From North
 Ellipsoidal distance	 S =		 1.2495 m

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Did you use HTDP to convert from NAD83 to WGS84? If not, then your coordinates were already off by 1.25 meters:

 

 TRANSFORMING POSITIONS FROM NAD_83(CORS96)   (EPOCH = 01-01-1992)
					  TO WGS_84(G1150)	(EPOCH = 12-08-2007)

		 INPUT COORDINATES   OUTPUT COORDINATES	INPUT VELOCITY


 LATITUDE	 35 49 54.04858 N	 35 49 54.06516 N	  1.35 mm/yr  north
 LONGITUDE   111 26 13.35218 W	111 26 13.39761 W	  1.14 mm/yr  east
 ELLIP. HT.		   1380.500		   1379.648 m	 -1.09 mm/yr  up
 X				-1892475.274	   -1892475.973 m	  1.67 mm/yr
 Y				-4819852.924	   -4819851.586 m	  1.14 mm/yr
 Z				 3713874.250		3713874.166 m	  0.45 mm/yr

 

Ellipsoid : GRS80 / WGS84  (NAD83)		
 Equatorial axis,	a   =	6378137.0000
 Polar axis,		 b   =	6356752.3141
 Inverse flattening, 1/f =  298.25722210088

 First  Station : NAD83						 
  ---------------- 
LAT =  35 49 54.04858 North 
LON = 111 26 13.35218 West  

 Second Station : ITRF00						
  ---------------- 
LAT =  35 49 54.06516 North 
LON = 111 26 13.39761 West  

 Forward azimuth		FAZ = 294  8 25.3681 From North
 Back azimuth		   BAZ = 114  8 25.3415 From North
 Ellipsoidal distance	 S =		 1.2495 m

 

 

That discussion has already been worn thin. The difference between NAD 83 and WGS 84 is so small as to be insignificant. If my GPSr will consistently put me that close to an adjusted mark, why would I wish to waste time and energy converting it to an outmoded datum.

 

We are not surveyors by profession, so having a $200 GPSr that will put us within a couple of feet of an adjusted mark sure beats paying $6,000 for one that will get you within 11.8110236 inches! $5800 to gain a foot in accuracy is a good deal?

 

John

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>30 centimeters = 11.8110236 inches

>Our handhelds will frequently (about 1 in 5 times) put us at 24 inches or slightly less when finding adjusted marks.

 

Well, the point I was kinda trying to make was that it seems to me that no consumer handheld has that kind of accuracy, and only professional gear has that level of accuracy. Neither Magellans or DeLormes fit into this catagory, but Trimble would.

 

At one point in time, I was actually considering a Trimble Juno, they're only $900, and small, about the size of any consumer GPS, and run Windows Mobile. But $900 is still pretty steep...

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>John said: The difference between NAD83 and WGS84 is so small as to be insignificant.

 

Well, if you are ignoring a difference between datums of 1.25 meter or about 4 feet, that is very significant to a discussion about how often the result is within 2 feet.

 

Does that model give different readings of a waypoint for NAD83 and WGS84 datum settings? I have yet to hear from anyone with a recreational grade unit that does indicate a difference.

 

A result that can be met 1 in 5 times isn't dependable enough to bother comparing against. How close you are 50% of the time or 90% or 95% is more meaningful.

 

The rounding error of the lat-lon is also of that same order of magnitude. Does this unit accept or display more digits than the typical rec grade unit? Typically +/- a half least digit of error is:

ddd mm ss.s +/- 5.1 ft (latitude)

or ddd mm.mmm +/- 3.0 ft

or ddd.ddddd +/- 1.82 ft

 

I've worked quite a bit at finding the ultimate accuracy I can get with my Garmin, by trying methods to get past the display rounding, averaging waypoints or track points for long times, on multiple days, and applying HTDP, etc.

 

I find that there is an internal computational precision limit in the Garmin 76S that makes error often 2 feet and sometimes 4 feet. You can see it by setting three waypoints several feet apart in a straight line and checking the pairwise distances it computes. So even with all the other tricks, to reliably measure a position to a few feet you need to also average in offset positions to deal with the computational precision. I'd like to see some tests on the Magellan to see if it handles this better.

 

John typically works under the best GPS conditions possible - wide open spaces where nothing blocks or reflects the signals. Still, there are ionospheric effects that WAAS doesn't provide localized enough data to eliminate and sometimes make errors of 10 or 20 feet that last for minutes to an hour. This, with the display rounding, and the datum difference make it very unlikely to achieve real-time accuracy of better than 5 to 10 feet half the time even under ideal conditions.

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What is the precision of the coordinates for an adjusted mark? 1/4 inch or less? Then having a receiver that has 30 CM accuracy is not very much better than The handheld units that we use when searching for survey marks. Is having a receiver that has 30 CM accuracy good enough to use professionally and determine a position or a boundary.

 

The only point I was making was when searching for marks whether I'm 1 foot, 2 feet or even 5 feet off when the GPSr zeros out, the odds are that I will find the station I'm looking for, unless it is buried. Then 1 foot off can be too much error, especially if the mark is buried several feet down.

 

Finding a station doesn't require the precision that setting does. It's all in what you intend to do with the GPSr.

 

John

 

edit: added 'inch' after the 1/4.

Edited by 2oldfarts (the rockhounders)

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... when searching for marks whether I'm 1 foot, 2 feet or even 5 feet off when the GPSr zeros out, the odds are that I will find the station I'm looking for, unless it is buried. Then 1 foot off can be too much error, especially if the mark is buried several feet down.

...

 

 

Precisely! :anicute:

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Did you use HTDP to convert from NAD83 to WGS84? If not, then your coordinates were already off by 1.25 meters:

 

 TRANSFORMING POSITIONS FROM NAD_83(CORS96)   (EPOCH = 01-01-1992)
					  TO WGS_84(G1150)	(EPOCH = 12-08-2007)

		 INPUT COORDINATES   OUTPUT COORDINATES	INPUT VELOCITY


 LATITUDE	 35 49 54.04858 N	 35 49 54.06516 N	  1.35 mm/yr  north
 LONGITUDE   111 26 13.35218 W	111 26 13.39761 W	  1.14 mm/yr  east
 ELLIP. HT.		   1380.500		   1379.648 m	 -1.09 mm/yr  up
 X				-1892475.274	   -1892475.973 m	  1.67 mm/yr
 Y				-4819852.924	   -4819851.586 m	  1.14 mm/yr
 Z				 3713874.250		3713874.166 m	  0.45 mm/yr

 

Ellipsoid : GRS80 / WGS84  (NAD83)		
 Equatorial axis,	a   =	6378137.0000
 Polar axis,		 b   =	6356752.3141
 Inverse flattening, 1/f =  298.25722210088

 First  Station : NAD83						 
  ---------------- 
LAT =  35 49 54.04858 North 
LON = 111 26 13.35218 West  

 Second Station : ITRF00						
  ---------------- 
LAT =  35 49 54.06516 North 
LON = 111 26 13.39761 West  

 Forward azimuth		FAZ = 294  8 25.3681 From North
 Back azimuth		   BAZ = 114  8 25.3415 From North
 Ellipsoidal distance	 S =		 1.2495 m

 

In the original NOAA professional publication titled "North American Datum of 1983" edited by Charles Schwarz, 1989, there is a paper "Relation of NAD 83 to WGS84" by Charles Schwarz.

 

In that paper, he explains that fundamentally NAD83 and WGS84 are computationally identical for all intents and purposes. The coordinate systems are identical. The ellipsoids are slightly different. The error introduced by doing calculations in one datum or the other amount to approximately about 1/10 of a millimeter at latitude 45 degrees.

 

However, he does explain why there are often differences of a meter or more in the two datums, and it has nothing to do with the coordinate system or the way calculations are performed or the ellipsoids that were used, it is almost entirely due to the errors in the observations that were used to obtain control points in either datum. (from this thread

 

That is from This Thread.

 

Hope you enjoy reading that old thread.

 

John

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Look closer at the second thread where caseyb asked for an experts opinion in this post, and you will find (trimmed for conciseness) this answer:

 

As such, in NAD-83 meters, the physical separation

between your points 1 and 2 would be:

 

d = SQRT(dx**2 + dy**2 + dz**2)

= 1494.914 millimeters

 

Like Dave Doyle said, if you're positioning at better than 3 meters,

this matters. If not, it doesn't.

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Look closer at the second thread where caseyb asked for an experts opinion in this post, and you will find (trimmed for conciseness) this answer:

 

As such, in NAD-83 meters, the physical separation

between your points 1 and 2 would be:

 

d = SQRT(dx**2 + dy**2 + dz**2)

= 1494.914 millimeters

 

Like Dave Doyle said, if you're positioning at better than 3 meters,

this matters. If not, it doesn't.

 

The key words here are "Positioning" and "3 meters" (just over 9 feet). We are not positioning, we are locating/finding and our GPSr is VERY Rarely off more than the 3 meters when searching for an adjusted mark.

 

John

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I'm not even sure where to ask this.......

 

In the bargain column of todays local paper, someone has a Trimble Juno SB for $99. I realize what this unit is, and I have a pretty good idea of what it's worth. It's in the bargain column, not the "for sale" section, and that has a price limit of $99, which makes me think he actually means to list it for that price. There's no way anybody would sell a legit unit for that price is there? The phone number he gave is a cell phone based in a city about an hour from here, and his outgoing voicemail message isn't in English. Those two things are enough to make me assume that this has to be a stolen unit and someone looking to unload it quick for a few bucks, right??

 

I'm SO tempted to buy it, play with it for a while, and sell it to someone who actually knows what it is. Thoughts??

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New price maybe $750? Half that in good used condition? Way more if it has software goodies? Software won't update and maybe won't run if you don't have the registration data?

 

If it was stolen and it has the owner's name, or the serial number can be traced, then you are out your $99, and have some unpleasant discussions with the police about buying something you knew was too good to be legit. Is it worth the risk?

Edited by Bill93

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You might consider talking to the local newspaper. I believe it is illegal for them to list items they know are stolen. Or, just forget about it.

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I just have to laugh and shake my head when people write that the difference between NAD83 and WGS84 (G1150) is insignificant. It is only insignificant if you're using a typical consumer GPSR with a crappy antenna, not collecting raw data and are not post processing. I'm measuring station velocity caused by plate tectonic motion. In that application the difference is huge! Not just the datum, but also the epoch. BTW, my total investment to reach the level of accuracy needed to monitor plate tectonic motion has been about US$1000. That includes GPSR ($350), geodetic tripod ($250), geodetic antenna ($250), coax cables ($50) and dc bias injector ($100). (The tripod and antenna are both used.) I collect raw data 24 hours at a time and post process using RTKLIB and nearby CORS reference station observations. I've recently measured the benchmark in my backyard as moving about 34mm/year to the Northwest. Assuming that this motion has been going on continuously back in time for eons, then that adds up to just under a meter of movement since I originally placed the benchmark (when I was much younger). It was my lifelong dream to be able to measure this and how I've done it.

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I just have to laugh and shake my head when people write that the difference between NAD83 and WGS84 (G1150) is insignificant. It is only insignificant if you're using a typical consumer GPSR with a crappy antenna, not collecting raw data and are not post processing. I'm measuring station velocity caused by plate tectonic motion. In that application the difference is huge! Not just the datum, but also the epoch. BTW, my total investment to reach the level of accuracy needed to monitor plate tectonic motion has been about US$1000. That includes GPSR ($350), geodetic tripod ($250), geodetic antenna ($250), coax cables ($50) and dc bias injector ($100). (The tripod and antenna are both used.) I collect raw data 24 hours at a time and post process using RTKLIB and nearby CORS reference station observations. I've recently measured the benchmark in my backyard as moving about 34mm/year to the Northwest. Assuming that this motion has been going on continuously back in time for eons, then that adds up to just under a meter of movement since I originally placed the benchmark (when I was much younger). It was my lifelong dream to be able to measure this and how I've done it.

 

Laugh and shake your head all you want. I have no desire to be a surveyor, set my own disk, or even worry about ground movement. As far as recovering survey markers is concerned, there is absolutely no difference between NAD83 and WGS84. I recover benchmarks as a hobby and don't feel the need to waste money on things that will not improve my chances of finding a specific benchmark. As I have stated before, the GPSrs that I use will consistently put me within 5 feet of an adjusted horizontal mark and they only cost about $220 each.

 

I'll return to my hobby now of finding survey marks and let you gloat over spending all that time and money on your personal benchmark.

 

John

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I'll return to my hobby now of finding survey marks and let you gloat over spending all that time and money on your personal benchmark.

 

Yes, I forgot that this is a benchmark hunting forum, not a positioning forum. Sincere apologies all.

Edited by astrodanco

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No apologies needed either way. It's all just relative. I happen to be doing some very exacting (important military type) electronics today. A consumer electronics user would say I'm nuts. It is all relative to what you need for a particular application. It's actually pretty amazing that one satellite system can serve both needs.

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Leica dual frequency survey grade (circa 2002)

 

13.jpg

MVC-005F.jpg

L61_MDOT_survey_2001.jpg

L61_1934-1.jpg

Edited by Z15

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