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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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Ontario
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.
 
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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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