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Do construction jobs need centimeter level accuracy?

Ask Ketchum

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Hello all,

I love near major city with plenty of construction projects on the go. For those of you in the drone construction services field what does it take to get started?

Is it required to have a surveyor on the team or subcontracted and GNSS RTK survey equipment/GCPs etc. for centimeter level accuracy or are most jobs just progress photos/videos and orthomosaics where positional accuracy is not paramout?

Thanks for the help,

Ash
 

jaja6009

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Hello all,

I love near major city with plenty of construction projects on the go. For those of you in the drone construction services field what does it take to get started?

Is it required to have a surveyor on the team or subcontracted and GNSS RTK survey equipment/GCPs etc. for centimeter level accuracy or are most jobs just progress photos/videos and orthomosaics where positional accuracy is not paramout?

Thanks for the help,

Ash
To get started I would make sure I understand maps in general. Coordinate systems, elevation and projections to name a few. Also know how to use GIS software. Elevation can be a tricky subject. Drone Deploy and Pix4D both assume that certain drones have elevations in their image metadata based off of a certain geoid. If this geoid is not going to output the expected orthometric elevations (NAVD88 for example), then you can have an unhappy client right off the bat. With Drone Deploy if you do not use GCPs to arbitrarily change to the required orthometric elevations you can run into trouble. Pix4D is more flexible and Agi Metashape allows you to use local geoids and the newest hybrid geoid 12 and 18 are available.

If offering maps based off of the drone's GPS you will basically have progression update maps.
Even with progression type outputs, to me it seems amateurish to have a series of maps as layers that do not line up with each other as will happen when not introducing control points. (Easily solved if after your first map you assign control points to features in the first map and use them as control points in subsequent maps). You will have relative but not absolute accuracy in terms of the first map to subsequent maps. And know how to output into a custom/local grid that may be used on a project.

Your second question depends on if you and your client agree to maps using highend GNSS control points and need absolute accuracy. Keep in mind though that their surveyors and engineers may not accept you as a geospatial partner. I have a full time job and cannot offer my progression services on a full time basis, maybe others will chime in on what the majority of their jobs are in terms of what accuracy is wanted the majority of the time.

Also, do not forget to check your state's laws regarding what a non-surveyor is allowed to sell. Some states do not allow you to state accuracy on a map or give volumes unless you are a PLS - Professional Licensed Surveyor. Google the case in North Carolina where a drone service provider is battling the state surveyor board on this subject.
 

Ask Ketchum

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To get started I would make sure I understand maps in general. Coordinate systems, elevation and projections to name a few. Also know how to use GIS software. Elevation can be a tricky subject. Drone Deploy and Pix4D both assume that certain drones have elevations in their image metadata based off of a certain geoid. If this geoid is not going to output the expected orthometric elevations (NAVD88 for example), then you can have an unhappy client right off the bat. With Drone Deploy if you do not use GCPs to arbitrarily change to the required orthometric elevations you can run into trouble. Pix4D is more flexible and Agi Metashape allows you to use local geoids and the newest hybrid geoid 12 and 18 are available.

If offering maps based off of the drone's GPS you will basically have progression update maps.
Even with progression type outputs, to me it seems amateurish to have a series of maps as layers that do not line up with each other as will happen when not introducing control points. (Easily solved if after your first map you assign control points to features in the first map and use them as control points in subsequent maps). You will have relative but not absolute accuracy in terms of the first map to subsequent maps. And know how to output into a custom/local grid that may be used on a project.

Your second question depends on if you and your client agree to maps using highend GNSS control points and need absolute accuracy. Keep in mind though that their surveyors and engineers may not accept you as a geospatial partner. I have a full time job and cannot offer my progression services on a full time basis, maybe others will chime in on what the majority of their jobs are in terms of what accuracy is wanted the majority of the time.

Also, do not forget to check your state's laws regarding what a non-surveyor is allowed to sell. Some states do not allow you to state accuracy on a map or give volumes unless you are a PLS - Professional Licensed Surveyor. Google the case in North Carolina where a drone service provider is battling the state surveyor board on this subject.
Thanks, that's very helpful. I guess the client would set the expectations regarding accuracy from the get go. If they do want ground control points and absolute accuracy, would they typically set and measure the points ahead of time or would the drone/survey company be responsible for doing this?

I am just trying to figure out if I should be investing in RTK GNSS survey equipment and training or if I can just subcontract that work out to a survey company if needed.
 

chasco

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Hello all,

I love near major city with plenty of construction projects on the go. For those of you in the drone construction services field what does it take to get started?

Is it required to have a surveyor on the team or subcontracted and GNSS RTK survey equipment/GCPs etc. for centimeter level accuracy or are most jobs just progress photos/videos and orthomosaics where positional accuracy is not paramout?

Thanks for the help,

Ash
It depends on the construction company. Most have not matured to the point that they require cm-level accuracy on grade. They may think they do but in my consulting experience many of them did not. This may be the difference between recommending they have their own program or subcontracting it out. We have several construction companies that we support on larger projects with stringent grading requirements. In-house we use RTK and/or GCP's every map.
 
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jaja6009

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Thanks, that's very helpful. I guess the client would set the expectations regarding accuracy from the get go. If they do want ground control points and absolute accuracy, would they typically set and measure the points ahead of time or would the drone/survey company be responsible for doing this?

I am just trying to figure out if I should be investing in RTK GNSS survey equipment and training or if I can just subcontract that work out to a survey company if needed.
You are asking a question that can only be answered by those who do this full time and also based on client expectation. I am sure that some clients may have a surveyor lay points, and others may want you to do it. Just be aware that just me talking to construction site managers I have found that a lot of them use a custom grid on site. If you are going to lay your own points but cannot tie into and then output into their custom grid, you may find lost customers. Go out and talk to some potential customers in your area as they are truly the only ones that can tell you what they would want. Maybe start easy and offer just a 2 series non-georeferenced progression map on a small site for free to show them what they could expect.

As far as GNSS equipment, Emlid RS2 units are a good budget choice. You can setup on known points and RTK or PPK your points. You can receive corrections over NTRIP as some states have free NTRIP access. Emlids now also allow you to set one unit over a known point and use their simple caster app to send corrections over the internet. Emlids are cost effective and very flexible. Also Trimble has a DA2 unit that is low cost and can connect to their Catalyst system and can offer low cm accuracy. Best part is that this service can be bought on demand in hour blocks. Be aware though that the greatest accuracy is through their VRS and it is not available in most of the country.

1637255411860.png

Their less accurate service covers the whole country. If you are in the areas above, then a low cost Trimble DA2 with On Demand VRS service might work for you.
 
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chasco

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You are asking a question that can only be answered by those who do this full time and also based on client expectation. I am sure that some clients may have a surveyor lay points, and others may want you to do it. Just be aware that just me talking to construction site managers I have found that a lot of them use a custom grid on site. If you are going to lay your own points but cannot tie into and then output into their custom grid, you may find lost customers. Go out and talk to some potential customers in your area as they are truly the only ones that can tell you what they would want. Maybe start easy and offer just a 2 series non-georeferenced progression map on a small site for free to show them what they could expect.

As far as GNSS equipment, Emlid RS2 units are a good budget choice. You can setup on known points and RTK or PPK your points. You can receive corrections over NTRIP as some states have free NTRIP access. Emlids now also allow you to set one unit over a known point and use their simple caster app to send corrections over the internet. Emlids are cost effective and very flexible. Also Trimble has a DA2 unit that is low cost and can connect to their Catalyst system and can offer low cm accuracy. Best part is that this service can be bought on demand in hour blocks. Be aware though that the greatest accuracy is through their VRS and it is not available in most of the country.

View attachment 3259

Their less accurate service covers the whole country. If you are in the areas above, then a low cost Trimble DA2 with On Demand VRS service might work for you.
This is exactly why we have a discovery meeting with every client. This frames what they know and do not know to inform them of any gaps and set realistic expectations of what will be provided. The contract is also present at this time. I always encourage our clients to use a Surveyor whether it be someone they know or that is actually present on the project. Despite the messiness of geodetic to grid or local you have no idea of what coordinates each project is on. Pretty much every company that uses GPS machine control works off of a localization and it may or may not be affected by a scale factor. Accuracy gets deep.
 

R Martin

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Thanks, that's very helpful. I guess the client would set the expectations regarding accuracy from the get go. If they do want ground control points and absolute accuracy, would they typically set and measure the points ahead of time or would the drone/survey company be responsible for doing this?

I am just trying to figure out if I should be investing in RTK GNSS survey equipment and training or if I can just subcontract that work out to a survey company if needed.
Every new building we raise has it's own control that is tied in to our grid. Might be done differently elsewhere but all projects are on some coordinate system; grid, surface, whatever. This is something that you iron out for each project well ahead of time in OAC meetings with the general contractor and subs if required as well as the client.
 

chasco

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Every new building we raise has it's own control that is tied in to our grid. Might be done differently elsewhere but all projects are on some coordinate system; grid, surface, whatever. This is something that you iron out for each project well ahead of time in OAC meetings with the general contractor and subs if required as well as the client.
The projects are on grid and the building are local in our case. Building corners are set by an RPLS and the building "grid" is localized to them. Our building crews then use a special optical instrument to stakeout that local grid and any points we have generated from BIM for walls, plumbing and such.
 

R Martin

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The projects are on grid and the building are local in our case. Building corners are set by an RPLS and the building "grid" is localized to them. Our building crews then use a special optical instrument to stakeout that local grid and any points we have generated from BIM for walls, plumbing and such.
Yuppers. That's usually how it's done.;) Unless its a state job and we just pull the numbers out of our backside...
 
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Ask Ketchum

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Thanks for the replies everyone. This sounds a bit over my head to be honest. I have a background in aviation but not very much experience in Civil Engineering/GIS/Surveying. Looks like I will either have to partner with someone or find a less technical niche like construction progress video/photos.
 

chasco

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Thanks for the replies everyone. This sounds a bit over my head to be honest. I have a background in aviation but not very much experience in Civil Engineering/GIS/Surveying. Looks like I will either have to partner with someone or find a less technical niche like construction progress video/photos.
It's not very hard as long as you have the right equipment which honestly is not that expensive given today's costs and inflation. A little understanding about the coordinate systems and their relationships will be easy for someone in aviation.
 

jaja6009

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Thanks for the replies everyone. This sounds a bit over my head to be honest. I have a background in aviation but not very much experience in Civil Engineering/GIS/Surveying. Looks like I will either have to partner with someone or find a less technical niche like construction progress video/photos.
It may seem overwhelming, but if you truly want to offer any type of GIS data, you really need to understand the concepts, terms, measurements and other aspects of what you will be working with. As Chasco stated, you already understand coordinate systems. Read up further on coordinate systems, geoids, ellipsoids and GNSS. Arc Maps has a $100 annual subscription package that allows you to play with the software and even features free training modules for you to follow. If you complete a lot of them you can really have a strong basis for the software.

If you can, start of easy. Offer a product of just showing progression. This is very easy as with cloud processing, anyone can do it now. See if Control Points can be laid for you by their surveyor as these would be the most accurate option anyway.
Know the laws about what data you can sell to clients.
Learn and start to implement more accurate data from introducing ground control.
As you said, team up with someone that already can do this as they will be great on the job training.
Be meticulous. I use a surveyor logbook to log all aspects of a site using their practices obtained from a college level surveyor textbook. This way I can always refer back to find out why a map may have inaccuracies.

Think of it like you being a pilot. You are not going to go from not being a pilot to flying IFR without doing the work.
 

Ask Ketchum

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It may seem overwhelming, but if you truly want to offer any type of GIS data, you really need to understand the concepts, terms, measurements and other aspects of what you will be working with. As Chasco stated, you already understand coordinate systems. Read up further on coordinate systems, geoids, ellipsoids and GNSS. Arc Maps has a $100 annual subscription package that allows you to play with the software and even features free training modules for you to follow. If you complete a lot of them you can really have a strong basis for the software.

If you can, start of easy. Offer a product of just showing progression. This is very easy as with cloud processing, anyone can do it now. See if Control Points can be laid for you by their surveyor as these would be the most accurate option anyway.
Know the laws about what data you can sell to clients.
Learn and start to implement more accurate data from introducing ground control.
As you said, team up with someone that already can do this as they will be great on the job training.
Be meticulous. I use a surveyor logbook to log all aspects of a site using their practices obtained from a college level surveyor textbook. This way I can always refer back to find out why a map may have inaccuracies.

Think of it like you being a pilot. You are not going to go from not being a pilot to flying IFR without doing the work.
Thanks for the tips, I will definitely spend some time studying GIS, doing practice flights and networking before going out to market my services. Is a Phantom 4 Pro a good drone to get started?
 

jaja6009

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The Phantom 4 Pro V2 is what I use for mapping and its mechanical shutter, 20MP, 1" sensor perform very well especially with dialed in Manual settings. I have a custom aftermarket PPK kit on the drone and also will use both PPK and GCPs but also just GCPs. My map with the best reported accuracy by comparison to control points was a small one with 5 GCPs and 5 Checkpoints, no PPK corrected images and the results were excellent. Actually I cannot state the mm level RMS error as in the X and Y horizontal it is slightly below GSD and accuracy cannot be under GSD.

1639185716273.png


The Autel Evo 2 RTK or Enterprise with RTK module is a very interesting new solution. You are basically only NTRIP/VRS (Internet corrections) or a known point with an Emlid Reach RS2 (Also can act as a caster to send out its own NTRIP) away from adding GNSS accuracy.
It has a 1" sensor, long flight times, the ability to swap camera payloads (The connection is not meant to swap payloads an infinite number of times in my opinion) and a stated cm precision in both RTK and PPK workflows, with the PPK workflow using a produced RINEX file.
A sister forum member JMason has been conducting some really interesting tests with this unit and the results have been very good. I am in no way an image expert, but I have read that Autel does a much better job in converting images to JPEG format and that many people claim that this helps with more points in your photogrammetry derived point clouds. It does lack a mechanical shutter which would enable you to conduct missions at a higher speed and help prevent the roller shutter effect, but the desktop applications like Pix4D and Agi Meta both have algorithms that can deal with it. You could also fly at a lower speed, but I would personally like to read more about others experiences and tests.

Link to Evo 2 RTK tests on sister forum. He has several threads on different tests, including thermal mapping and is a wealth of information on this new drone with his tests that he posts for all members to view.
 
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chasco

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Thanks for the tips, I will definitely spend some time studying GIS, doing practice flights and networking before going out to market my services. Is a Phantom 4 Pro a good drone to get started?
For a non-RTK drone less than $1800 the Phantom 4 Pro is still the best mapper you can get. Just stay away from the "+" models. If you intend to continue with mapping and get deeper into accuracies you will want to make your way to an RTK drone sooner rather than later. Or you'll need to invest in some GNSS equipment. I would keep the brand in mind whether it be DJI or Autel. Things like batteries, chargers and props will all cross over. Personally we fly the Yuneec H520E RTK which is a slightly larger hexacopter but I would still choose the Autel Evo II Pro RTK over the Phantom 4 RTK although they are hard to come by and Autel could not give us a definite answer as to when they will be available again. Poor timing right before the holidays...
 

Ask Ketchum

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For a non-RTK drone less than $1800 the Phantom 4 Pro is still the best mapper you can get. Just stay away from the "+" models. If you intend to continue with mapping and get deeper into accuracies you will want to make your way to an RTK drone sooner rather than later. Or you'll need to invest in some GNSS equipment. I would keep the brand in mind whether it be DJI or Autel. Things like batteries, chargers and props will all cross over. Personally we fly the Yuneec H520E RTK which is a slightly larger hexacopter but I would still choose the Autel Evo II Pro RTK over the Phantom 4 RTK although they are hard to come by and Autel could not give us a definite answer as to when they will be available again. Poor timing right before the holidays...
Thanks. I think I will just go with the phantom 4 pro without RTK and upgrade from there. I am trying to keep my start-up costs as low as possible to see if I enjoy mapping and if there is a market for it in my area. Worst case I can keep the phantom 4 pro for regular photo/video work.

In terms of GNSS equipment it seems like it may be cheaper to get a phantom 4 pro without RTK and an Emlid reach RS2 compared to a autel evo II Pro RTK with the base station. Alternatively I can probably subcontract the work out to a surveyor on my early jobs before investing in GNSS equipment.

I also think I will likely have to upgrade my computer setup for processing if I do it locally and buy software for mapping such as Agisoft Metashape or a Pix4D subscription.
 

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