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Cost effective ways to obtain GPS data for Ground Control Points

Roger Wilco

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As an Amazon Kindle Unlimited subscriber, I downloaded a free copy of Jim Crume's excellent "GIS Mapping (Bad Elf & Metashape Pro)" volume that describes the use of the $600 Bad Elf GPS receiver to perform surveying by drone. The paperback copy of this book is $14.

Info is here: GIS Mapping: Step by Step Guide (Survey Mapping Made Simple Book 11), Crume, Jim, eBook - Amazon.com

The cover of the book shows the Bad Elf GPS receiver in action, sitting atop a tripod to obtain the GPS coordinates of the corner of a painted parking lot line.

Best regards -- Roger
 
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AMann

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Emlid.com has several options for centimeter accuracy measurements at low prices, including a set of base and rover GPS stations for under $1700 for both. I just sold mine in the classifieds here - you can see what they look like there.
 
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R.Perry

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Great tools, but unless you are a licensed surveyor you can not claim your mapping is survey grade even if it is. Also I found even with the GCP points known the drones accuracy isn't up to survey accuracy. My comment to the client is, it's close but no cigar.
 
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JDL

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So what can you do? orthos? I’ll have to look into it here in Pennsylvania
 

JDL

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Great tools, but unless you are a licensed surveyor you can not claim your mapping is survey grade even if it is. Also I found even with the GCP points known the drones accuracy isn't up to survey accuracy. My comment to the client is, it's close but no cigar.
I hear you but it also sounds like you can’t even deliver them or produce them
 

R.Perry

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I hear you but it also sounds like you can’t even deliver them or produce them
No, you need RTK drone to get survey accuracy. Most states require surveyors to be licensed, that's why you can't claim your mapping to be a survey.
 

R Martin

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So what can you do? orthos? I’ll have to look into it here in Pennsylvania
Maps that are centimeter grade. I can get near-survey but I am not an RPLS so I don't have the math to back it up (or the state seal for that matter). Our orthos are at least accurate to within 1/2" if not better. Good enough to digitize subsurface utilities from which is what we do for a living. I use AeroPoints for job control and we also have an RPLS set benchmarks (this is included in the contract) on each site prior to construction (I set my base station up on the closest benchmark and stream real-time corrections to the aircraft as it is doing it's thing so I don't have to do any post-processing correction with the data. The AeroPoints are "survey-grade" (read that accurate to about 10mm) and I use them as checkpoints to ensure that the aircraft GPS was operating properly and there weren't any hiccups during the flight.
 

R.Perry

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Maps that are centimeter grade. I can get near-survey but I am not an RPLS so I don't have the math to back it up (or the state seal for that matter). Our orthos are at least accurate to within 1/2" if not better. Good enough to digitize subsurface utilities from which is what we do for a living. I use AeroPoints for job control and we also have an RPLS set benchmarks (this is included in the contract) on each site prior to construction (I set my base station up on the closest benchmark and stream real-time corrections to the aircraft as it is doing it's thing so I don't have to do any post-processing correction with the data. The AeroPoints are "survey-grade" (read that accurate to about 10mm) and I use them as checkpoints to ensure that the aircraft GPS was operating properly and there weren't any hiccups during the flight.

What are you flying? The only way I could get that kind of accuracy was in post by using the surveyors GCPs, I normally included a minimum of five GCPs when I uploaded to DD. Was your 10 mm accuracy both horizonal and vertical? Now I did find our volume and excavation elevations very accurate, or I should say the engineering department did.
 

R Martin

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What are you flying? The only way I could get that kind of accuracy was in post by using the surveyors GCPs, I normally included a minimum of five GCPs when I uploaded to DD. Was your 10 mm accuracy both horizonal and vertical? Now I did find our volume and excavation elevations very accurate, or I should say the engineering department did.
I'm basing the previous statement off of GPS points. Horizontal accuracy is pretty close. Vertical is not as accurate (one of the limitations of GPS). I claim between 3/8 - 1/2" of accuracy per pixel based upon the processing report. While the Aeropoints are able to derive millimeter accuracy, to produce a ortho like that is beyond my capabilities. I'm just not that good using Pix4D.
 

JDL

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So then in producing orthomosaic maps, I spoke to a local surveyor who also uses drones and he said I’m good to go in our state, just no property lines etc. and I plan on making a disclaimer regarding using the tools within pix4dcloud deliverable, that they are not survey grade or accurate, although they sure can be close at times(measuring horizontally with no gcp)
 

R Martin

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What are you flying? The only way I could get that kind of accuracy was in post by using the surveyors GCPs, I normally included a minimum of five GCPs when I uploaded to DD. Was your 10 mm accuracy both horizonal and vertical? Now I did find our volume and excavation elevations very accurate, or I should say the engineering department did.
BirdsEyeView Firefly 6 Pro with a Sony RX1R2 42mp camera in terrain following mode slaved to AllTerra's RTK network with an independent base station set on a surveyed benchmark. The numbers quoted are from Pix4D's processing report. As to their accuracy, I am not a surveyor so I can't prove the numbers.
I use 10 GCP/checkpoints per flight; half on the boundary (because it is an odd shaped tract) and the other half scattered in the center to reduce float.
 

chasco

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Emlid.com has several options for centimeter accuracy measurements at low prices, including a set of base and rover GPS stations for under $1700 for both. I just sold mine in the classifieds here - you can see what they look like there.
I'll second the Emlid, but be aware of the less expensive RS+ units as they are single channel L1 only. If you are in a wooded or urban area with tall structures a single channel receiver can have trouble maintaining a fixed solution and you will end up learning PPK.
Their multi-channel RS2 units are vastly superior and in par with the much more expensive Topcon, Trimble and Leica hardware. They are $1899 per receiver, but compare that to $15k per for the big 3 brands.
Last but not least investigate NTRIP services. Many states have free mount points, but even a subscription would be well worth not having to use a base station. I would highly recommend this path.
 

R.Perry

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Wow, 10 GCPs, did you find any variations? My question always was since we can't claim survey accuracy why worry about it unless the surveyor's want to use it? I only shot mappings with GCP's when the superintendent requested it, otherwise it was a bunch of stitched pictures they could look at and zoom in, do their inspection while sitting at their desks drinking coffee.
 

chasco

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Wow, 10 GCPs, did you find any variations? My question always was since we can't claim survey accuracy why worry about it unless the surveyor's want to use it? I only shot mappings with GCP's when the superintendent requested it, otherwise it was a bunch of stitched pictures they could look at and zoom in, do their inspection while sitting at their desks drinking coffee.
We use GCP's because we are tieing to the surface coordinate system from the design files and comparing ground progress against the design as we go. To even get close to accurate quantities for cut/fill requires survey-grade accuracy.
 
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