GCP Marker Questions

So for GCP markers we’ve been using the Rock Robotic recommended black and white fabric markers. I have a 16 mile corridor scan coming in January with potential for some heavy winds as well as some curious homeowners that might move my markers… I don’t want to carry plywood sheets into these areas either. I saw a project that one Rock user did on this months newsletter where he just had a spray paint template made of carboard that he would put on the ground and then spray white and pink squares around the GCP. I am curious if anyone else has done this method and how well it worked, any colors work better than others? The other item is there is a possibility for snow on the ground in some areas, that’s a whole other issue but I am wondering if the white color for a target might be more difficult to locate in intensity view if paired with snow in the surrounding area?

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I have made spray targets. In the summer, they are harder to see than the black n white targets (I use painted aluminum squares), but in the winter…

These are utility locates, in the snow they glow brilliant.

In my corridor scans, I use manholes, train tracks, easy road marking and curves on the road (beginning an end of arc). In the wilderness, my black n white targets and some “invisible” control to keep my elevation checked.

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Here’s our article on GCP Best practices: Ground Control Points (GCPs) Best Practices

Hope this helps!

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@FlyingRadioWaves So those locates how do they appear in intensity view? They certainly do pop against the snow!

@daniel.windham I’ve read that article and its what we use normally but like I mentioned before I am not going to carry full size sheets of plywood into the boonies along 16 miles of floodplain and our “cloth” markers I think will blow away and/or the contrast from snow against the white might be difficult to discern in intensity view. I understand spray paint markers wouldn’t be the best option for the data but for ease of layout for my team, in the field conditions we expect, I am hoping it will be a quick and easy option in this instance. Have you guys done any studies on spray paint markers at all?

I’ve tried spray paint many times, sometimes you can see it pretty well, other times you can barely make them out. I’d suggest trying to fly a low pass over the targets if you can to give you a better chance. I have used a variety of colors and I think white works the best on grass but if it’s snowing you may be better off with orange/pink.

On any issues like this where I’m trying GCP options I usually just got set each type in a test area (like my yard or something) and I go fly at the same height/speed as my project will be flown at that way I can see what I can expect.

We’ve had pretty good results using cloth checkerboard targets in the snow. The black should stand out well against all the white. You could also add a black border (2-3" wide) around the target, which helps quite a lot. Our targets have grommets in the corners, so we use spikes to hold them in place. You could really use anything heavy though, just be careful not to cover too much of the target.

I wouldn’t rely on paint, but we have used it in a pinch. We used dark blue/black paint on top of the snow to create a checkerboard pattern. You’ll have to use quite a bit of paint though, a simple X will not be visible enough. I’m not sure which colour works best. We’ve also had some luck just clearing the snow off the topsoil to create a checkerboard pattern. As Daniel mentioned, lowering the altitude of the drone will really help to differentiate the intensity of the different colours/materials. Just fly your mission as normal and then manually take over to lower the drone above each target.

I would be more concerned about flying in windy conditions with snow sitting on the ground. Both of these will really affect the accuracy of your data.