What Are floor manage points (GCPs) and how do I exploit them?
A manual to the use of ground manage factors with Drone Mapping software.
In case you work with drone mapping software program, you’ve no doubt heard speak of floor control points (GCPs). Used regularly inside the surveying industry, as well as in digital design and production, GCPs greatly growth the worldwide accuracy of drone maps. Even though they’re now not vital in each state of affairs, GCPs are a critical device for precision mapping. But what exactly are ground control factors? And the way do you pass approximately using them efficiently?
To help crack the code on floor manage points, we’ve put together this brief guide to using GCPs with drone mapping software.
What are ground control points?
So what precisely are ground control points? Ground manage factors are big marked goals at the floor, spaced strategically throughout your region of hobby. if you use ground manage factors along with your aerial map, you first want to decide the RTK GPS coordinates at the middle of each. (We’ll provide an explanation for how to try this touch later.) The ground control points and their coordinates are then used to help drone mapping software appropriately position your map with regards to the actual world round it.
It is probably helpful to think of your GCPs as a sequence of thumbtacks positioned on your drone map. Because the drone mapping software program knows the exact region of each of those “thumbtacks”, it may reference their places while it matches up all of the different factors on the map.
When and Why Are GCPs important?
When used successfully, floor control factors greatly improve the global accuracy of your drone map. This is to mention, they help make certain that the latitude and longitude of any factor to your map corresponds correctly with real GPS coordinates. That is essential in situations in which precision mapping and genuine worldwide accuracy are wished. As we referred to above, surveying corporations normally use GCPs, due to the fact a excessive degree of worldwide accuracy is essential in most of the paintings that they do. Virtual design and production is another sector that frequently requires this level of precision drone mapping.
Land point, a surveying enterprise primarily based in Louisiana, makes use of floor control factors whilst developing drone maps used for topographical surveying. Using GCPs on an eighty five-acre map, their crew conducted a correct aerial survey, saving over eighty man hours compared to standard land survey methods.
Each drone mapping task is particular, and not all projects require a excessive degree of worldwide accuracy. due to this, it’s miles crucial to evaluate each mission for my part earlier than you decide to take the more step of the usage of GCPs. but generally speaking, projects like geo-referenced overlays, layout documents and land name surveys benefit from the use of ground control points. In an upcoming publish, we’ll take a deeper examine which kinds of initiatives are quality suited for the usage of GCPs.
The way to construct a floor control factor
There’s no one proper manner to make a ground control factor. One critical component to remember is that the GCP have to be without difficulty visible on your aerial imagery. This is performed by means of the use of high-comparison shades and by means of making sure the ground control factor is huge enough to be visible out of your specific flight altitude. We commonly suggest flying at 300 feet with a front lap and side lap of 70/seventy five when the usage of floor manages points. Take into account that this will exchange based upon the location you’re mapping. Research greater through studying our recent publish approximately mapping accuracy and reviewing our GCP help files.
Some of organizations do promote pre-made, transportable floor control points. However, many drone customers virtually style their personal.
This properly built GCP turned into spray painted onto the concrete the usage of a stencil. Word that the marker is huge sufficient to be seen from some distance away. a middle mark enables dispose of any confusion as to wherein the center point is positioned.
If you’re unable to mark GCPs with paint, there ar a variety of low-value ways in which to create markers with things to be had from any neighborhood hardware keep. The climate-resistant rubber and vinyl markers seen above emerge as costing approximately $five each and are very durable.
Measuring the area of Your GCPs
As we cited above, it’s miles vital to degree the GPS coordinates on the center of each floor manipulate point. To try this, you want either a actual Time Kinematic (RTK) or publish Processing Kinematic (PPK) GPS receiver. Trimble and Leica merchandise are commonly used for high-accuracy GPS measurements. New, decrease-price alternatives have these days come onto the marketplace as well. Hiring a surveyor to degree the region of your floor manage factors is likewise an alternative.
Does not use a cell phone or pill to degree the location of your ground manage points? The accuracy of these devices is very much like that of a drone’s onboard GPS gadget and will not deliver precise effects. Alternatively, use one of the preceding techniques listed above, including an RTK or PPK GPS receiver.
Distribute at least 4 GCPs around your place of interest, ensuring to create a buffer zone of fifty–one hundred feet at the fringe.
Satisfactory Practices for using floor manage factors with Drone Mapping software program
Of direction, if you use floor manage points with drone mapping software program, its miles essential to use them efficaciously. Comply with these nice practices to assist make certain your GCPs serve their meant motive and enhance the accuracy of your map.
Use at the least 4 big GCPs: Drone Deploy requires no less than 4 grounds manage factors. Every have to measure at least 4 feet. No more than 10 are normally wanted for larger maps.
Frivolously distribute your GCPs on the floor: For maximum maps of slight size, we advocate 5 GCPs, one positioned close to every corner and one placed inside the middle, as pictured above. Additionally, ensure GCPs are spaced a long way enough aside, to avoid confusion. As a popular rule, if you could see a couple of GCP in an picture, they’re too near collectively.
Create a buffer quarter around your map’s perimeter: We recommend a buffer zone among the edges of your map and any floor manage factors. This ensures there’s enough image coverage to carry out reprocessing. The scale of your buffer region need to be somewhere between 50–one hundred ft, relying on the overlap of your flight. A better overlap produces more snap shots and typically calls for much less buffer region.
Be privy to elevation adjustments: If the area being mapped has sizeable elevation changes like hills, mines and valleys make sure to place at least one floor manage point on every of the extraordinary major elevations.
Make certain your GCPs are unobstructed: visual obstructions like overhangs, snow, color or glare make ground manage points tough to identify for your drone map.
Understand Your EPSG code: before processing your map in Drone Deploy, you have to input the EPSG code that relates on your GPS measurements. Select your EPSG code through modifying the settings of your GPS measurement device. In maximum cases, we advocate using WGS84 (EPSG: 4326).