Minimum Overlap

[ArrUnTuS]

What are you using for your GCPs and checkshots that are that quick? There's no post-processing beyond uploading the data and opening a website. If you've got a workflow that quick than I think you're going to put us all out of business.

I am not using, I will implement it, but the tests say that RTK, in 15 minutes the base has connection. Then fly the drone. I'm wrong and in such a short time it doesn't establish the position?

 

[UAV_Mapper]

I'm wrong and in such a short time it doesn't establish the position?

Probably getting a bit off topic, but it really depends on the network you're using, the equipment, distance to your control stations, etc. We have some GCPs that are GPSed for multiple hours because that's what is required to hit our job specifications. The control portion is easily the longest and most difficult part of any of our aerial mapping projects; flying is the easy part.

On a typical job, we have 4 rover methods and it'll depend on if we're within cell range to a correction network (VRS), want to use a satellite correction (RTX), want to use RTK to a radio base, or post-process to a non-radio base (PPK). Then we check-in to a minimum of 5 existing monuments, which may be several miles from the project site and may or may not still exist, so it's a bit of an easter egg hunt. Then we start shooting the GCPs and gathering check shots. We'll usually GPS our GCPs for 5-10 minutes (depending on the setup used) and hit our topo checkshots for up to 3 minutes (sometimes longer). After the field, everything is run through Trimble Business Center and there's usually some arguing about which monuments to hold and which base stations to use. The grid coordinates are converted to ground coordinates, but the scale factor depends on the specific project that we're doing. Then... we have our final locations for loading into Pix or PhotoScan.

So, when there's a product that gives us reliable results by placing them on the ground and picking them back up after 45 minutes, it's pretty appealing. Our biggest issue is that we like to have topo check points for accuracy calculations, so we already have to have a rover in the field. But if we have a less demanding project or only volume calcs, I'd like a set of APs to use for simplicity sake.

 

[ArrUnTuS]

Probably getting a bit off topic, but it really depends on the network you're using, the equipment, distance to your control stations, etc. We have some GCPs that are GPSed for multiple hours because that's what is required to hit our job specifications. The control portion is easily the longest and most difficult part of any of our aerial mapping projects; flying is the easy part.

On a typical job, we have 4 rover methods and it'll depend on if we're within cell range to a correction network (VRS), want to use a satellite correction (RTX), want to use RTK to a radio base, or post-process to a non-radio base (PPK). Then we check-in to a minimum of 5 existing monuments, which may be several miles from the project site and may or may not still exist, so it's a bit of an easter egg hunt. Then we start shooting the GCPs and gathering check shots. We'll usually GPS our GCPs for 5-10 minutes (depending on the setup used) and hit our topo checkshots for up to 3 minutes (sometimes longer). After the field, everything is run through Trimble Business Center and there's usually some arguing about which monuments to hold and which base stations to use. The grid coordinates are converted to ground coordinates, but the scale factor depends on the specific project that we're doing. Then... we have our final locations for loading into Pix or PhotoScan.

So, when there's a product that gives us reliable results by placing them on the ground and picking them back up after 45 minutes, it's pretty appealing. Our biggest issue is that we like to have topo check points for accuracy calculations, so we already have to have a rover in the field. But if we have a less demanding project or only volume calcs, I'd like a set of APs to use for simplicity sake.

I don't have a lot of experience but I've seen RTK systems work and it's the one that convinces me the most. I don't know where you are, but here in Spain the VRS networks seem to have good coverage. This is a very important fact.

I have made an exhaustive study of the different methods to use the best, those that you have commented and I believe that for speed RTK system is the best, everything depends on networks does not require postprocessing and the data are quite reliable. It is always advisable to take a few checkpoints to verify that the data taken by the rober are correct.

Normally this type of technical work is usually done for technical companies, topographers, etc., which have their own systems, and are those that with L1 L2 can verify or contrast the other data.

With the system I've looked at you can also put a rober on a mast so you can catch CGP's as well although being the same system to use later with the drone I don't know if it makes much sense to do it. On site, there are usually fixed verifiable points and they can also be used as a help or check.

The AeroPoints I have to say that the delay (supposedly 2 hours, 45 minutes would be a much better option) and the price makes me discard it. It takes a lot of different jobs to pay for it. Anyway, I'm open to suggestions

 

[John Githens]

When i started getting experience with photogrammetry a couple of years ago, I reached out to several surveyors in my rural location. Only one even returned my call and invited me in for a meeting. Turns out he was not that interested in the technology but more interested in lecturing me about not offering surveying services without a license. He was pleasant enough, but my attempts to do exactly what you mention were fruitless. I suggested that he have me come to a site they were already surveying and I would set air targets on their markers and provide him with the resulting orthoimage. I suggested he give me the surveyed location of 3/4 of the targets and reserve the rest to prove the ortho. I offered this for free for him to evaluate the technology and workflow.

He wasn't interested and I was disappointed. I hold out hope that some day, one of these guys will become interested.

There must be a few interested Licensed Surveyors out there, but I've only met one. However after many tests and discussions a conclusion was reached that the cost of setting the essential GCPs in the field for sufficient model accuracy, plus the cost and risk of developing and maintaining in-house photogrammetry knowledge and skills, appeared to outweigh the potential for economic gain from transitioning to using drone systems. At least at this time for primarily boundary line survey jobs. The calculation may be revisited later with a different conclusion, or if there were more local clients interested in the views possible from 3D Site Models. As a side note, one can read concerned comments in the Licensed Surveyor community that it's becoming difficult to entice new people into the business to replace those retiring or expiring. Perhaps the lure of DRONES would entice more enrollees to train to be a Surveyor. That said, ultimately there has to be a good business case for a surveying company of some size, based in a particular location, to decide to take the risk and start to make the transition to more complex operations.

 

[Dave Pitman]

There must be a few interested Licensed Surveyors out there, but I've only met one. However after many tests and discussions a conclusion was reached that the cost of setting the essential GCPs in the field for sufficient model accuracy, plus the cost and risk of developing and maintaining in-house photogrammetry knowledge and skills, appeared to outweigh the potential for economic gain from transitioning to using drone systems. At least at this time for primarily boundary line survey jobs. The calculation may be revisited later with a different conclusion, or if there were more local clients interested in the views possible from 3D Site Models. As a side note, one can read concerned comments in the Licensed Surveyor community that it's becoming difficult to entice new people into the business to replace those retiring or expiring. Perhaps the lure of DRONES would entice more enrollees to train to be a Surveyor. That said, ultimately there has to be a good business case for a surveying company of some size, based in a particular location, to decide to take the risk and start to make the transition to more complex operations.

From reading a LOT of forums, mostly for uas but also for surveying, there seems to be much more interest in integrating uas outside of the US, particularly in Canada, Australia and South America to name a few. I live in the Pacific Northwest, and uas aerial photogrammetry is not the right tool in many instances because of dense forrest and vegetation. However there is still plenty of opportunity to save a lot of man hours on certain projects. In those cases, points are going to be surveyed anyway. In the case of DEMs to establish topography, if it's not covered by vegetation and is of any significant size, there is just no way land-based surveying can compete with properly executed uas photogrammetry products. Not to mention fast audits of material removal or fill on earthwork.

Oh well, I'm sure there are plenty of surveyors that get it. Just not near me for now.

 

[UAV_Mapper]

I think that @Dave Pitman and @John Githens are hitting on some important points about the state and use of UAV technology in professional environments. When I first started, I had a hard time trying to get engineers, architects, and surveyors to buy into the technology, but that was 4 years ago, so it was ancient by today's standards. Now I work for a company that has flown manned aircraft for 60 years and we fly traditional photogrammetric missions. The transition to UAV work here has been widely accepted and we're having great success filling in the gap between the small 2-man survey projects and the >1000 acre manned aircraft flights. Another reason for our success is that we're in a desert state and the highest vegetation that we have to deal with is 2 feet off the ground.

As the industry grows and becomes for pervasive, I think that there will be much greater adoption by almost all entities. We're also seeing a huge decline of our traditional surveyors and with most states requiring some sort of licensure for creating maps, there should be a greater pull towards the field. We always say that pilots are easy to get, it's getting knowledgeable people to process and understand the data that's hard.

 

[R Martin]

Thanks for all the input and advice.
How do you suggest obtaining ground control points and how many are needed?

A bare minimum is five. One for each corner and one somewhere in the middle. The four corners anchor the ortho and the center point prevents interior float. The larger the area the more points you need. 200 acres = roughly 10 GCPs.

You should set GCPs with an accurate GPS unit. A mapping grade GPS will suffice unless you need survey-grade data. If you do not have a GPS unit that is capable (and cell phones don't count), then you might contract either an RPLS for survey-grade points or for mapping-grade points. The accuracy you need depends upon the accuracy requirements of the job. Volumetric calculations and site surveys would need more accurate GCPs. A development orthomosaic would not.

 

[R Martin]

I live in the Pacific Northwest, and uas aerial photogrammetry is not the right tool in many instances because of dense forest and vegetation.

Simple solution: Lidar. Sees through dense vegetation. Of course the cost....