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Precision GPS on a budget  

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mattmers
(@mattmers)
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Joined: 2 months ago
Posts: 3
September 9, 2018 10:01 pm  

I am a undergraduate at a university in Kansas that is currently working on a degree in Earth Science with minors in Paleontology and GIS. I have been doing Paleo field work in Montana for the past 4 years and we have generally used outdated handheld gps units. Unfortunately the university I go to had their surveying GPS unit broke a few years ago and they have not replaced it. I was wanting to get this communities input on cheap high precision units or DIY units. I was wanting something with cm precision since I would be working on mapping fossil beds. 

I have seen a few articles on DIY high precision gps units but I'm not sure if they have improved since then and if they would be ideal to my scenarios. I would ultimately either spend my money or work it into a undergrad research proposal. Also to cut cost I'd probably want something that can either connect to a pc or smartphone.

https://spectrum.ieee.org/tech-talk/transportation/self-driving/cheap-centimeterprecision-gps-for-cars-and-drones

https://www.instructables.com/id/Sub-Centimeter-GPS-With-RTKLIB/

https://gizmodo.com/5405804/make-your-own-real-time-kinematic-gps-receiver-thats-accurate-to-one-centimeter

 

Any feedback or thoughts would be appreciated. 


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zammo
(@zammo)
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Posts: 67
September 10, 2018 3:06 am  

Hey mate,

            How accurate exactly do you require? I'd assume you need survey grade accuracy for paleo work, and I don't think you could guarantee this with a home made unit. If it is only for academic use try contacting a local survey equipment dealer and they may have some decent secondhand units available. Some manufacturers may also have supply agreements with educational institutions, at least that used to be the case here in Oz.

Maybe a browse on ebay may also find some gold for you.

 


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StLSurveyor
(@stlsurveyor)
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Posts: 1347
September 10, 2018 4:08 am  

I got into Surveying via Archaeology fieldwork. After graduation from my undergrad I took a job with an Archaeology firm for two seasons. I was exposed to the Total Station and the layout of sites and metric grid patterns. We never used a GPS unit but our baselines and main points were tied down with GPS. I assume this is probably still the same process?

I would recommend this one for your baseline observations:

https://ig3s.com/

Or this one:

https://www.javad.com/jgnss/products/receivers/triumph-2.html

 

Good Luck! Rock Chalk!

Professional Surveyor - MO, AR, KS, KY
sUAS Certified Pilot


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Bill93
(@bill93)
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Posts: 4958
September 10, 2018 5:58 am  

I like the idea mentioned above of getting a baseline using gnss and working off it with a total station.  That ties your work to the world and then quickly and more accurately maps each feature you are interested in. 

Some of your features may not be in good GPS locations but the baseline can be chosen for good reception.

You can't quickly get as accurate relative positions with GPS as with TS especially the height, which I expect is critical to your work.

A static session for OPUS or similar processing can run for hours on a baseline point while you do other work and an older cheaper receiver will serve, while getting similar accuracy in near real time on a feature takes newer and expensive gear, if even possible. 

The archaeologists I'm acquainted with often place reference points and use a sub-meter GPS on them but then locate features and artifacts with total station.

I am amazed at what they can deduce when they have a file of precise coordinates and category on each and every item. Long items get coords on each end. They can then plot distributions in 3-D by type and think about what it means

This post was modified 2 months ago 2 times by Bill93

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aliquot
(@aliquot)
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Posts: 842
September 10, 2018 7:46 am  

I assume the cm accuracy requirement is only for relative positions, meaning you want to know exactly how each item you find is related to all the other finds, not the exact position of each find on the face of the earth (why would you care to know the exact distance from a particular fossil to an arbitrary control point miles away?)  If that is the case a total station would be a much better tool. You could then use your handheld GPS to assign meter level accuracy positions to your project.

If you need cm level accuracy for elevations GPS is the wrong tool. It can be done, but only with very expensive units and very long occupation times. 

If you don't have to work alone you can probably find a used total station that will do what you need for well under $1000. You don't need anything fancy. GPS for the same purpose will cost you much much more, and require more training.  If you you are confident with basic algebra and trigonometry you can learn everything you need about a total station from its manual and a basic surveying text book. 

Even a surveyor with the best GPS system available needs to use a total station sometimes. If you are under very heavy canopy or up against a cliff you wont get cm accuracy with any GPS. 

Another thing to consider, do you really need cm accuracy? Will your conclusions change if the position is off by 2 or 3 cms? 

This post was modified 2 months ago 2 times by aliquot

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DC Kelley
(@dc-kelley)
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Posts: 13
September 10, 2018 8:26 am  

Its a pity, but it seems doubtful you will have a nearby existing Base Station you can use for this. so you will need to bring your own.

If as aliquot observes you only need tight relative accuracy (<1cm)  over a small area (a few km) then you idea to use a cheap L1 only device and RTKLIB is very viable if you can put up with the DIY aspects.  A pair of these and suitable antenna sets (do not be cheap there), and the rest of the setup is free.  Total cost under 1k plus last years laptop and a Wifi node.  I have dragged this sort of thing into the field will good sucess many time over many years.  But is is visual kludge, and as noted a used total station should be your next item. 

This post was modified 2 months ago by DC Kelley

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gschrock
(@gschrock)
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September 10, 2018 9:03 am  

Swift has a developer kit that is quite affordable.

And they have standalone multi-constellation multi-signal boards (with an extra chip for user loaded software) for under $600.

Similar offerings from UBLOX

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mattmers
(@mattmers)
FNG Member
Joined: 2 months ago
Posts: 3
September 10, 2018 5:23 pm  

Well clearly I need to look more into this. I really don't know the difference between the different systems you all have mentioned. I was hoping for something accurate, quick and cheap. Sounds like I'm dreaming. Paleontologist generally work more rapidly than paleontologist from what I've seen.  We usually pull out a specimen in a few day compared to archeologist. Maybe I should just use existing consumer grade gps and look into photogrammetry. 

 

Also for those interested and nearby. The St. Louis Science Center will have an event called "Rock Fossil Quake" on Saturday the 22nd of Sept. It is a Earth Science event with talks from geologist and paleontologist. 


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Skeeter1996
(@skeeter1996)
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Posts: 608
September 10, 2018 7:40 pm  

We can't give away GPS equipment that isn't GNSS capable these days. A Trimble 5800 System will give you subcentimeter positions, just not under trees

 If your local Surveying Dealer wouldn't just give you an old system I'd be surprised. Check EBay, there are some dirt cheap nonGNSS systems on there. A Dealer would be your best 1st bet. If you're not in trees a nonGNSS system will work just fine for you 


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