DISPOSABLE HI-VIS GCPS ARE HERE
New hi-vis colors, new matte finish, 100% bio-degradable
EVOLUTION OF AEROTAS GCPS
Aerotas has continued to iterate on the initial GCP design
At Aerotas, we care about the details. That is how we have helped land surveyors get the most value out of their drones since 2014. One detail that is ubiquitous among drone surveying projects, but rarely discussed in depth is the actual marking of ground control for drone surveys. But this is one of many issues that matter a lot to us and our clients. It is one of many details that, cumulatively, make the difference between a survey-grade product, and just a pretty picture. Earlier this year, Aerotas released the first version of our ground control points, and we have slowly and quietly rolled out a few updates since then, acting on the thoughts and experiences of our clients out in the field. Here, we wanted to take the opportunity to discuss the entire decision-making process of our ground control points in depth.
Throughout all of our work, Aerotas focuses on continuous, incremental improvements, and this is true with our GCPs as well. The first test versions of our GCPs were printed on standard 8.5x11 printer paper, quickly followed by taping squares of construction paper together to test the right sizes. Every batch of GCPs that we have produced has been improved from the prior batch, and this is a process we intend to keep using so that we are always getting better.
Our research has shown that a significant amount of field time is spent setting, and then picking up ground control targets, so a simple way to save a huge amount of time is to simply not pick up your GCPs. However, most GCPs available for purchase are expensive at $5-$10 per target and made from materials like vinyl or plastic which will litter the property for years to come. Because of this, we knew from the outset that our GCPs had to be made from 100% biodegradable materials so that they could be left behind without causing environmental damage. Our first production version satisfied this goal, but the ink and coating that we initially chose to use created a slightly hydrophobic effect that limited the ability of the GCPs to absorb water, which makes them take longer to bio-degrade. All recent versions have been manufactured with a new and more absorbent process to increase the permeability of the paper, speeding up the degradation process when outside.
Color is a surprisingly complex topic. Part of that is because color, as humans perceive it, is highly dependent on the context of what is around it. For ground control points, one of the main things we are trying to achieve with color patterns is creating a form of “anti-camouflage” where the control points do not blend in at all to the surrounding environment. That is why our original GCPs use blue and orange as the main colors, both of which rarely appear in nature (assuming you aren’t surveying the top of the water that is). Further, from a distance, these colors blend together to create purple, which still stands out well in most scenarios.
But in some desert and bare-earth environments, the orange that we used can blend into the color of the ground, so we decided to release a second color pattern as well. This pink and green, which we refer to as “watermelon” internally, stands out very well on earth-moving projects or in the desert where the color green is rare. However, our traditional blue and orange tiles should be used in grassy or vegetated areas where green is more prevalent because the blended average color of pink and green comes out to an almost olive color.
Most traditional GCPs are a simple black and white, and for most people, this has been good enough. However, we knew we could do better. The reason black and white have persisted for so long is simply due to the lower cost of manufacture and availability of products. However, black and white both occur regularly in the field (think concrete and asphalt) so they easily blend in. Further, they average to gray, so from a distance, they can become invisible. High contrast, anti-camouflage colors are far more effective than black and white.
Anyone who has tried multiple types of ground control will know that a shiny target is typically not a good target. Especially on clear, bright days, highly reflective targets will reflect the bright sky, even from multiple angles, resulting in a washed-out white blob where the ground control point ought to be. So keeping reflectance low is critical. Unfortunately, most common paper and printing methodologies result in a more reflective surface than we would like to see. That is why, after our first version of ground control, we re-worked the formula to make it less reflective, which has the added benefit of making the GCPs more biodegradable. However, this had the unintended side-effect of changing the color profile. Because we use a subtractive color (See: https://en.wikipedia.org/wiki/Subtractive_color) manufacturing process, a change in the reflectivity of the raw paper changed the appearance of the color profile, even though the ink did not change. That is why we had to alter the colors in our latest version of our ground control to maintain the right apparent color profile while still having a very low reflectance.
The best size for a ground control point depends on who you ask. For a photogrammetrist who is looking at the photos on a computer screen, the bigger the GCP the better. But of course, setting six-foot-wide targets in the field is a huge pain for surveyors in the field. Size is ultimately a balance between the difficulty of carrying/setting up GCPs in the field, and finding them in the photos after the project is flown.
We have found that 12” x 12” is the most common size for simple GCPs. These work great at 200’ AGL or lower (assuming 20MP sensor) but can be very difficult to see otherwise. Larger ground control points, like the 19” x 19” Propeller AeroPoints, are easy to see from high altitude, but large enough that they are difficult to carry under one arm. Our GCPs, at 16” x 16” attempt to find the right balance of easy to carry and set, and easy to see in the field. They have 78% more surface area than 12” squares and are small enough to carry hundreds in a typical field truck without modifications.
Weight & Thickness
Anyone who has worked with vinyl kitchen tiles as GCPs knows that weight makes a huge difference in usability. These tiles, despite their small 12” x 12” size, wind up being extremely heavy. However, if you go too far on the other end, there are problems too. Cloth GCPs will easily fold over in the wind if only held down by a single point, so it typically takes 5 nails to anchor a single GCP. Our GCPs are constructed by what is effectively 0.014” thick cardstock. This is designed to be a light as practical, while still being sturdy enough to withstand wind even with just a single nail in the center. While you still might need to anchor down the sides in very windy conditions, we have found this to be the best balance between usability and durability.
Our Latest GCPs
Combining all of these factors into a single product requires finding the Goldilocks zone of ground control points. We have to find the right balance between durability, size, environmental friendliness, usability, and of course, cost. Our latest GCPs are the best we have ever made by every measure.
Aerotas provides data processing and linework drafting services to land surveyors and civil engineers. The same level of thoughtfulness and detail we put into making our ground control points goes into every project we work on. Click the link below to learn if aerotas linework might be right for you.