Ground Control Points (GCPs) for aerial photography

Hi guys,

We would like to share with you very simple find we did during our operations. Making reusable Ground Control Points (GCPs) for aerial photography and photogrammetry.

We spend a lot of time testing and tuning our Universal Ground Control Software U[g]CS in a real world scenarios.

For aerial photography and photogrammetry you can rely on modern software like Pix4D, Acute 3D and other to produce good results without ground control points. If good is not enough and accurate 3D model or digital map needs to be rendered you always need GCPs.

We started from “classic” crosses made from painted plates of cardboard, wood and plastic, but they proved not to be practical in every situation and all weather conditions we encountered.

And finally we found that best material for small GCPs is simple ceramic tiles:

For each GCP you need 2 black and 2 white tiles with mat surface. Glossy has reflections and does not work well.

They are absolutely water (rain/snow), wind and mud resistant. Can be easily transported in car and reused almost forever. Until human error takes its toll and you drop them on rocks or hit hard against a car.

Tiles with 40X40 cm size proved good for making shots from up to 100 meters.

This is a shot taken from approx. 50 meter altitude with GoPro:

Zoomed in part of the frame above:

Good luck and safe flights,

UgCS team

You should fly back and forth along a line on both sides of it.

An important point - you need to get a good overlap (~80%) of images on the conductor's level. For that you need to know approximate conductor's altitude.

Also pixel size on conductor's level should be at least as half of conductor diameter.

To simplify calculations you can use Photogrammetry tool (available only in paid versions of UgCS). Draw any area, specify GSD = conductor diameter/2, forward overlapping = 80%, side overlapping = 70%. Select appropriate camera action (trigger by distance or trigger by time).

UgCS will calculate altitude, distance between survey lines and time or distance between shots.

Next you can manually draw your route along powerline. Use calculated distance between survey lines as distance between your back and forth flights, add conductor's altitude to calculated altitude and use calculated distance or time between shots.

Last important step - you MUST check minimum distance from drone to conductors. It depends on line voltage.

And NEVER fly under conductors.

Good luck :)

You need to be a member of diydrones to add comments!

Join diydrones

Comments

Alexey Dobrovolskiy February 20, 2017 at 1:27am

Hi, as I remember we used all settings by default.
Geoff Thomas February 19, 2017 at 6:38pm

Hi again, do you have any advice for what settings to use in Pix4d to get it to resolve the wires into the point cloud? I have collected imagery now and am about to process it. I made sure to fly as per your advice above and the wires show up clearly in the imagery.
Geoff Thomas January 9, 2017 at 3:31pm

Awesome! Thanks for your help!
Alexey Dobrovolskiy January 9, 2017 at 1:40pm

You should fly back and forth along a line on both sides of it.

An important point - you need to get a good overlap (~80%) of images on the conductor's level. For that you need to know approximate conductor's altitude.

Also pixel size on conductor's level should be at least as half of conductor diameter.

To simplify calculations you can use Photogrammetry tool (available only in paid versions of UgCS). Draw any area, specify GSD = conductor diameter/2, forward overlapping = 80%, side overlapping = 70%. Select appropriate camera action (trigger by distance or trigger by time).

UgCS will calculate altitude, distance between survey lines and time or distance between shots.

Next you can manually draw your route along powerline. Use calculated distance between survey lines as distance between your back and forth flights, add conductor's altitude to calculated altitude and use calculated distance or time between shots.

Last important step - you MUST check minimum distance from drone to conductors. It depends on line voltage.

And NEVER fly under conductors.

Good luck :)
Alexey Dobrovolskiy January 9, 2017 at 1:40pm

You should fly back and forth along a line on both sides of it.

An important point - you need to get a good overlap (~80%) of images on the conductor's level. For that you need to know approximate conductor's altitude.

Also pixel size on conductor's level should be at least as half of conductor diameter.

To simplify calculations you can use Photogrammetry tool (available only in paid versions of UgCS). Draw any area, specify GSD = conductor diameter/2, forward overlapping = 80%, side overlapping = 70%. Select appropriate camera action (trigger by distance or trigger by time).

UgCS will calculate altitude, distance between survey lines and time or distance between shots.

Next you can manually draw your route along powerline. Use calculated distance between survey lines as distance between your back and forth flights, add conductor's altitude to calculated altitude and use calculated distance or time between shots.

Last important step - you MUST check minimum distance from drone to conductors. It depends on line voltage.

And NEVER fly under conductors.

Good luck :)
Geoff Thomas January 9, 2017 at 11:36am

Hi, What flight path / flightplan do you recommend to successfully capture the transmission line wires as shown in the first image?
Alexey Dobrovolskiy February 10, 2015 at 8:29am

Yes. We used Pix4D Discovery - free version.
Michael Kagalenko February 10, 2015 at 5:20am

The first photo looks like a point cloud that successfully captures overhead transmission line wires, is that right? Do you made those with commercial soft, or the open-source one?
Alexey Dobrovolskiy February 9, 2015 at 8:33am

Ok, we will share our Excel macros and experience.
Daniel Perez February 9, 2015 at 6:17am

Thats very interesting, we are working on a similar project in my country but we must do thermography to each tower and create and autonomous inspection line. Maybe we could share experiencies and stay in touch.

thanks

of 3

This reply was deleted.