Creating Ground Control Points


#1

Does anyone know how a regular old drone pilot such as myself, can affordably create Ground Control Points using some kind of handheld GPS that is NOT $1,000 or higher? This is a hurdle I really need to overcome for some large quarry clients I’m trying to secure.


#2

Unfortunately to get real accuracy (cm level) you need to get a professional grade GPS unit (often around $10k)

Having said that, I’ve heard of people creating ground control points with a simple GPS and that helps a bit (m-level accuracy).


#3

Hi Helios,

Mike is correct. I have done this type of work several times. I have a client that wished to have 400 acres scanned and mapped to the nearest level of accuracy. The area was a rock quarry just as you seem to have encountered. After mapping it with 80/80 overlap, I was able to get 5ft. of accuracy. I have a fried who is a survey professional and we discussed letting him set some GCPs with his 30K survey equipment which I gladly accepted. After remapping the same area, the accuracy was 3cm (about 7 inches) which, as he explained, is survey accurate. I went back a third time with a handheld GPS device, placed it in the center of each marked GCP measured by the expensive survey equpiment, recorded the lat/lon/alt. and at each GCP, could already tell the handheld position was moderately different. I then flew the quarry a third time with the handheld GPS information and the accuracy was 3ft. So, if a client wants survey grade accuracy, using a professional surveyor to set the GCP is the best way to give the client what they want. In the end, you will pay the surveyor for his work but only for the first time. Every time after that, you already have the information for the subsequent flights.

Interesting results on calculating volumes based on a comparison of same stock piles from each of the three flights . . . . measurement differential average was just shy of 1%. This, I believe, shows how good DD is at processing viable, usable data for less cost. The cost for a surveyor will have to be passed on to the client but if your results are +/- 1% from results of drone mapping, then I’m not sure what the need of centimeter level accuracy is at that point. But, if that is what your client wants, that is what your client should get.

If you want to demonstrate to potential clients (mining/quarry), once you get one producer to agree to a demo, it would be worth hiring a surveyor to set your GCPs, fly the area and then go back and fly it without the use of GCPs. Then compare the two as it relates to volume calculations, slope grading, etc. I believe you will see that the difference will be minimal. If that is the case, show those results to the client and let them know that if they want their other assets mapped (lots of quarries are owned by corporations; therefore they have more than one) you can save them a lot of money by not having to have centimeter level accuracy. If your client still wishes to have survey accuracy, then you can develop a partnership with a licensed surveyor that might give you a lower rate if you agree to always use them when needed. Agree to put their company name and contact information on your website under a heading of “partnerships”.

Hope this helps give you some good ideas.


#4

Hello, Have a look at https://emlid.com/shop/reach-rtk-kit/ and check out their users forum. Lots of info. It’s the setup I’ve got and a lot of others are using it for just what you’re after. A low cost(around $600-800) high accuracy rtk survey kit, but with a learning curve and how steep it is depends how familiar you are with survey and gis. :slight_smile: I wasn’t familiar at ll with it but now I’m really starting to have fun.Good luck.


#5

Thank you all so much. That’s some GREAT information. This current quarry client does not need survey grade accuracy. Just volumetric measurements. However, I definitely plan on trying to develop a relationship with some kind of survey company. What a great idea. I have some solar power company that may need the survey grade accuracy in the future. Great stuff folks. Thanks.


#6

Dale, for me 3ft is good enough, what handheld unit are you using to get that kind of global accuracy?


#7

I was using my surveyor friend’s Trimble GeoX7. Its a high dollar unit but did not require the full RTK set up thus saving a lot of setup time.


#8

Very insightful, thank you for sharing, Dale.


#9

Cool to see you’re experimenting with this- agreed that some familiarity with GIS is helpful when learning to work with GCPs. What do you see as the challenges of use? Are the calibrations difficult? Anything you can share is appreciated!

Best,
Neema


#10

Neema, I would have to say that the hardest thing for me, as a complete beginner, was learning about gps, gnss, and GIS in general. If you purchased the Emlid Reach rtk kit already familiar with the terminology and and a basic knowledge of this field, calibrations would not be difficult at all. You just follow directions and away you go. For example, using this for measuring a few ground control points is simple. You have the option of using either relative accuracy or absolute accuracy. If you only need ground control points for producing orthomosaics, it doesn’t matter if you have cm level accuracy in real world coordinates, as long as they’re accurate relative to each other and the area they’re located in. Then you can just set up on site and go. If you need cm level absolute accuracy, you should have a known point within 10 km of where you are doing you’re measuring and mapping.


#11

Makes sense- appreciate the follow up!


#12

Like Dale said, I use a cm-accuracy Geo7 Trimble unit, on a Virtual Reference Station (VRS) network. The trick with my unit is that I rent it - for about $200/day, I can set all the ground control I want, and then simply return the unit when I’m finished.

About an hour of training (usually provided by the Trimble vendor) is all it takes to be able to use the unit; if you can run a smart phone, you can survey ground control points.

Something that might be worth looking into.


#13

Depending on what state you are in, you may be in a gray area with the law. Performing surveying without a license is illegal.


#14

hi guys, 3’ is not accurate enough you need to locate your GCP to 3cm accuracy.

you can try to piece together a system for 1,000$ with single frequency parts and figure out software etc but you will wait forever for a position that is good and will spend hours with a mess of wires and software… instead come check us out here.

http://www.epocdronesurvey.com/

this is what we do… we can help you


#15

Our company plan on upgrading to this unit soon.


#16

In response to the subject of surveying without a license, I have consulted an attorney on the issue and his opinion is this: Drone operators are gathering aerial geo-spacial data and forwarding it to a client. If a client wants an aerial map that is considered accurate, then the drone operator can only do their best to provide as accurate data as possible. What the client does with the data after the fact is up to them. As a drone operator, I do not advertise that my results are good enough to mark official land boundaries at the courthouse or with the State. That job is for PLS experts. I do not survey; I gather aerial data. If this is against some licensing requirement, then I can’t wait for someone to contact Google to tell them they can not do scanning anymore since it is considered surveying without a license or satellite imagery companies to tell them the same thing. If surveyors were smart, they would either get their Part 107 certificate or “team” or “partner with” a licensed UAV pilot to provide them with aerial data for their business. That is my opinion and I’m sticking to it.


#17

I love the concept but to be honest, I have been burned a couple of times with this “kickstarter” crap. NO MORE. If you really want to promote your product, send me a set and I will test it. If it works, I will be online on DroneDeploy singing your praises. If it doesn’t work, then it will back up my feelings on Kickstarter. Ball is in your court.


#18

Probably the best advice I’ve read on this subject so far.


#19

Have a look at Emlid ReahRS:
its a RTK reciever for 800$, so if you have a reference station network (CORS) available, chances are good this will give you centimeter accuracy


#20

Thanks Brent. I think you pointed out the real questions many of us have i.e. the difference between real world versus relative accuracy. Can you recommend a methodology for relative accuracy given the GCP that the surveyor has marked in the perimeters of a parcel of development land? That is, without the need of costly equipment.