Cost effective ways to obtain GPS data for Ground Control Points

[Clinton Carman]

Hello Everyone,

Our company has been doing a lot of drone mapping as of late. We've been working primarily on a lot of back country that is quite remote, very steep and was often involved in a wildfire. Most of what our clients have wanted is visual information only. The ability to see what was burned, what wasn't, to count trees, etc. However, in that process we've contemplated implementing a system to utilize ground control points into our data intake to increase the accuracy of our maps.

I understand we can hire a land survey crew to come out and take measurements at various GCP's and incorporate that data for survey grade work. That's not what I'm looking for. What I'm looking for is a similar solution that we can do on our own and will help us improve the accuracy of our maps that (short of survey grade) will work for most people.

I've heard of various ways of doing this but don't have much experience in the GIS/Mapping industry yet so I don't know if I'm missing something, or what solution would the most cost effective. One solution I've seen is to buy the self contained AeroPoints by PropellerAero. You have to buy 10 of them for $6,000, but they do all the work for you, you just lay them out in place and take the measurement, then fly the map. Other solutions would be to have our own placards that we lay down and determine the GPS coordinates ourselves using some kind of Trimble system, or something similar. I've seen Reach RS system, or the 3DR GCP with a Trimble Catalyst antenna as devices.

TL;DR - We want to be able to record GPS coordinates for our own GCP's, do you know of a cheap way to do that without hiring land surveyors?

Any recommendations from you guys/gals?

Thank you in advance!

 

[AerialCS]

That new phantom 4 RTK survey drone has some interesting enhancements...check it out

 

[Carl Friis-Hansen]

Hi Clinton,
you can buy a hand held device for about $700, which will give you cm precision after a certain amount of minutes.
Drawback is that you will have to wait for those minutes at each of your GCPs.
There is, as far as I know, only one company making them. When I find my notes about the device, I will inform you here.

 

[DavidRansier]

This is a great Thread! I’ve been researching this very topic, and for clarity, the P4-RTK doesn’t solve th GCP issue. You may not require GCP’s with the P4-RTK, but they help with added accuracy. You can’t use the P4-RTK toget GCPcoordinates, or so I’m told from a DJI dealer.

 

[MavicMapper]

A GCP is just a base point that is used to tie in a given area to a known coordinate system. If I were you, I would check your county’s survey records (should be available online) and go hunt for a monument from a public land survey corner, 1/4 corner or 1/4 1/4 corner. Then you could just place a photogrammetric target atop the monument (line up center of target with center of monument) and incorporate this area into your mission when you fly so that you capture the target in your scan. This way you can tie your map or point cloud into a coordinate system of your choice from a well-established point of record.

 

[MapMaker53]

Along those same lines, if an established survey monument is not within your flight area, I would think you could have a number of painted metallic targets that are welded to long metal rods made by a local metal shop, and then hammered into the ground in a few open canopy areas by a field person who is equipped with a hand-held GPS unit to note the exact coordinates of each for your capture.

 

[R Martin]

TL;DR - We want to be able to record GPS coordinates for our own GCP's, do you know of a cheap way to do that without hiring land surveyors?

Any recommendations from you guys/gals?

Thank you in advance!

Trimble (and others) have a selection of GPS units that will allow you to obtain your own Northing and Easting measurements that can then be applied to your processing software for georeferencing. Accuracy and functionality depends upon the unit (and cost). We utilize 2 Geo 7X handhelds with Zephyr antennas and a mapping package and I believe they ran around $20K each. The software that works with the units to process the information is currently Trimble Business Center and I think that is 10K plus yearly maintenance.
Another solution would be purchasing a set of Aeropoints which will set you back about $6200.00 without tax. They are survey-grade GPS units that you set out on the job site and then use the numbers in your post-processing of the orthomosaic. They also have software associated with them but it is not necessary to purchase the software. They will work independently.

 

[Jim Dow]

You can try using curved flight lines to a) minimize the use of GCPs and b) mitigate the SfM doming (elevation) error - see attached image. You should only need 4 to 10 GCPs depending on the size and characteristics of the target area. Also, if you want to gather your own GCPs, I would recommend the BadElf GPS unit (about $650) which will give you better than a meter horizontal accuracy without post processing - yet post processing capability is available. Avoid the drone RTK solutions.

 

[Paullo]

The most cost effective approach would be to not use ground control points at all but to improve the positional accuracy of the orthomosaic by georeferencing against existing satellite imagery using GIS. This will not be survey grade accuracy (but you didn't need that) but will be an improvement on the accuracy afforded by the onboard GPS. A tutorial for doing this using QGIS (free open source software) is here: Georeferencing Aerial Imagery — QGIS Tutorials and Tips

 

[Russ Still]

I don't know if they provide the resolution that you need, but you can easily get the lat/longs using ForeFlight, or even just click "Mark my location" using the maps app on an iPhone.

 

[R Martin]

Hello Everyone,

Our company has been doing a lot of drone mapping as of late. We've been working primarily on a lot of back country that is quite remote, very steep and was often involved in a wildfire. Most of what our clients have wanted is visual information only. The ability to see what was burned, what wasn't, to count trees, etc. However, in that process we've contemplated implementing a system to utilize ground control points into our data intake to increase the accuracy of our maps.

I understand we can hire a land survey crew to come out and take measurements at various GCP's and incorporate that data for survey grade work. That's not what I'm looking for. What I'm looking for is a similar solution that we can do on our own and will help us improve the accuracy of our maps that (short of survey grade) will work for most people.

I've heard of various ways of doing this but don't have much experience in the GIS/Mapping industry yet so I don't know if I'm missing something, or what solution would the most cost effective. One solution I've seen is to buy the self contained AeroPoints by PropellerAero. You have to buy 10 of them for $6,000, but they do all the work for you, you just lay them out in place and take the measurement, then fly the map. Other solutions would be to have our own placards that we lay down and determine the GPS coordinates ourselves using some kind of Trimble system, or something similar. I've seen Reach RS system, or the 3DR GCP with a Trimble Catalyst antenna as devices.

TL;DR - We want to be able to record GPS coordinates for our own GCP's, do you know of a cheap way to do that without hiring land surveyors?

Any recommendations from you guys/gals?

Thank you in advance!

I use Aeropoints and they work really well as long as you set them where they get a good unobstructed "view". Like any other GPS instrument, they are subject to multipathing errors when in a built-up or obstructed environment. For $6250.00, they are an affordable solution when compared against even a mapping grade GPS unit that is robust and reliable (we own both). Also look at a Trimble Geo 7X with a mapping software package....I think they are running around $18,000.00 if I remember correctly but I do have CRS. I'm sure that there are cheaper solutions available; Garmin for example.
Keep in mind if you are doing your own GPS work that the hardware is only part of the package. You will also need the software to process the data you collect and Trimble Business Center (TBC) will run another $10,000.00 base without modules which you will need at least one....

 

[Jullie]

You can try using curved flight lines to a) minimize the use of GCPs and b) mitigate the SfM doming (elevation) error - see attached image. You should only need 4 to 10 GCPs depending on the size and characteristics of the target area. Also, if you want to gather your own GCPs, I would recommend the BadElf GPS unit (about $650) which will give you better than a meter horizontal accuracy without post processing - yet post processing capability is available. Avoid the drone RTK solutions.

Hello Jim this is the first time I heard about curve lines can you explain how and why you increase the quality of the map?thanks

 

[Paul Suthard]

Using handheld GPS units like Garmins or even the Trimble Geo's will get you close, but not good enough. Remember that every second of latitude is 100' on the ground and so then every 1/10th of a second is 10 feet. That's as tight as the consumer grade GPS units will get you. That's as good as using GIS, which is not good if you are trying to turn out a product with any sense of reproduceablility. As a surveyor, we set GCP's on our sites and it usually takes about 15 minutes to collect the GPS data on each point. So for a half a days work ($600-$800 you could have permanent reference points with sub-centimeter accuracy and a product that would be acceptable to any engineering/surveying firm.

 

[R Martin]

Hi Clinton,
you can buy a hand held device for about $700, which will give you cm precision after a certain amount of minutes.
Drawback is that you will have to wait for those minutes at each of your GCPs.
There is, as far as I know, only one company making them. When I find my notes about the device, I will inform you here.

There are actually a lot of companies making a handheld unit. And yet accuracy is an elusive word. Your equipment can be accurate to within a centimeter or two but if you don't set it up right, that accuracy is a moot point. You just inaccurately collected accurate garbage. Look at Trimble, Garmin, Topcon and a host of others for examples of accurate units that will give a a chance at getting a solution. For $600-700 though, your accuracy is always going to be suspect. Our handhelds with their bipods, antennas and other associated hardware ran around $16,000 to 18,000 a pop for centimeter grade accuracy.

 

[R Martin]

Using handheld GPS units like Garmins or even the Trimble Geo's will get you close, but not good enough. Remember that every second of latitude is 100' on the ground and so then every 1/10th of a second is 10 feet. That's as tight as the consumer grade GPS units will get you. That's as good as using GIS, which is not good if you are trying to turn out a product with any sense of reproduceablility. As a surveyor, we set GCP's on our sites and it usually takes about 15 minutes to collect the GPS data on each point. So for a half a days work ($600-$800 you could have permanent reference points with sub-centimeter accuracy and a product that would be acceptable to any engineering/surveying firm.

$600 -800 for a control point? That's a deal. Our local shops charge double that for a USGS style monument for each monument. Don't get me wrong; they are the most accurate way to ensure site control on our jobs, but I get the impression that you are low-balling the price.

 

[Florida ProFly]

Hello Everyone,

Our company has been doing a lot of drone mapping as of late. We've been working primarily on a lot of back country that is quite remote, very steep and was often involved in a wildfire. Most of what our clients have wanted is visual information only. The ability to see what was burned, what wasn't, to count trees, etc. However, in that process we've contemplated implementing a system to utilize ground control points into our data intake to increase the accuracy of our maps.

I understand we can hire a land survey crew to come out and take measurements at various GCP's and incorporate that data for survey grade work. That's not what I'm looking for. What I'm looking for is a similar solution that we can do on our own and will help us improve the accuracy of our maps that (short of survey grade) will work for most people.

I've heard of various ways of doing this but don't have much experience in the GIS/Mapping industry yet so I don't know if I'm missing something, or what solution would the most cost effective. One solution I've seen is to buy the self contained AeroPoints by PropellerAero. You have to buy 10 of them for $6,000, but they do all the work for you, you just lay them out in place and take the measurement, then fly the map. Other solutions would be to have our own placards that we lay down and determine the GPS coordinates ourselves using some kind of Trimble system, or something similar. I've seen Reach RS system, or the 3DR GCP with a Trimble Catalyst antenna as devices.

TL;DR - We want to be able to record GPS coordinates for our own GCP's, do you know of a cheap way to do that without hiring land surveyors?

Any recommendations from you guys/gals?

Thank you in advance!

Hello Julie.
We have the same goals. We use Pix4d desktop and utilize three types of GCPs. First, we measure a few things on the ground with a construction measurement tape. Secondly, we place GCP checkerboard markers strategically in areas without interest, and thirdly we use an Emlid Reach Base and Rover. The Emlid is very affordable and you can connect to a correcting server for your points. We use Florida DOT transmitters. As we collect a point, FDOT servers correct it. These three GCP methods are then put into Pix4d to tighten your resulting map. It is also very helpful to have an RTK or PPK drone. The RTK does not provide exact geo-reference, but it does help the drone collect it in a more fixed position than a non-RTK.
I can answer more questions if you would like. Just email me I can offer more Emlid and drone brand information recommendations based on our experiences.
Rachel

 

[Paul Suthard]

$600 -800 for a control point? That's a deal. Our local shops charge double that for a USGS style monument for each monument. Don't get me wrong; they are the most accurate way to ensure site control on our jobs, but I get the impression that you are low-balling the price.

There is a big difference between an USGS (NGS) monument and a photo ID point with a target. I would double or triple the amount I quoted if permanent reference points to that degree are set. The information on both types of points is the same, one is permanent, the other is not so much.

 

[R Martin]

There is a big difference between an USGS (NGS) monument and a photo ID point with a target. I would double or triple the amount I quoted if permanent reference points to that degree are set. The information on both types of points is the same, one is permanent, the other is not so much.

That sounds reasonable.

 

[Clinton Carman]

Hello Julie.
We have the same goals. We use Pix4d desktop and utilize three types of GCPs. First, we measure a few things on the ground with a construction measurement tape. Secondly, we place GCP checkerboard markers strategically in areas without interest, and thirdly we use an Emlid Reach Base and Rover. The Emlid is very affordable and you can connect to a correcting server for your points. We use Florida DOT transmitters. As we collect a point, FDOT servers correct it. These three GCP methods are then put into Pix4d to tighten your resulting map. It is also very helpful to have an RTK or PPK drone. The RTK does not provide exact geo-reference, but it does help the drone collect it in a more fixed position than a non-RTK.
I can answer more questions if you would like. Just email me I can offer more Emlid and drone brand information recommendations based on our experiences.
Rachel

Thank you everyone for your responses. This is along the lines of something I'm looking for. I am not a surveyor. I will not attempt to sell survey-grade work. I also don't want to pay $16,000 - $18,000 for something I use sparingly, and only to increase my own confidence in my products. Again, the point of all of this is to tighten up the accuracy of the map. With only using the on-board GPS system, the variance in the Z direction could be as much as 10 meters!! That's where I've been at, and I'd be happy with getting it to a few meters, or sub-meter if possible. I do not need centimeter grade accuracy. If I ever do need that level of accuracy, I'll hire professionals with professional equipment to mark out GCP's before I fly.

The Emlid does seem to be a good alternative and at a good price point. Which models do you find work best for you? I want to do all my GCP work after the map (PPK) as opposed to while flying (RTK).

 

[Roger Wilco]

Gentlemen, the Bad Elf company has a couple of GPS receivers that would economically satisfy your need for GCP location.

They have a hand-held unit with approx. 1 meter accuracy for $600.

A unit with 1 centimeter accuracy goes for $2500.

Information is here: GIS & Mapping.