This is special surveyor paint, which can be purchased at most any survey supply (usually in cases of 12 cans). Paint may be applied to rapidly find the nail while walking or flying. This is more common a special nail that has grids or a detented point for precision, is driven into the ground and spray paint marks the area. The Ground Control Points (controls), may be mobile, or may be painted on the ground as seen below. These might be captured using a variety of GPS systems, such as the DT Research 301 (pictured here), with a rod and bi-pole over a Hoodman Ground Control Point system, or perhaps something more elaborate such as a Leica GS18 receiver or a more affordable, yet less flexible Emlid RS2 Base/Rover system. This is good enough for most sorts of aerial precision work.įirst and foremost, we need a known point, if we’re using only UA and a Base station or NTRIP corrections system. It is very, very accurate, providing capability of 1cm (.39”) in horizontal and 1.5cm in vertical precision. The collective nodes feed a server, which aggregates the location data between the nodes and satellites, and sends out a correctional data stream, informing a “rover” device of it’s actual location in XYZ space. The NTRIP nodes/stations are fixed at known positions, and are constantly receiving satellite location data. For example, NTRIP is heavily used by agriculture, driverless cars, area inventory management, surveyors, engineers, departments of transportation. This server constantly broadcasts GPS data via wifi, and is used to provide wireless transmission of location data to many different industries. The NTRIP server is in constant contact with GNSS nodes surrounding many areas of the United States. NTRIP data is transmitted via RTCM, which carries the correctional information. Some regions provide the NTRIP data connection at no cost (usually through a State or municipal service) or for a nominal, typically annual, fee. In order to use this type of correction, a cellular modem, a receiver capable of RTK correction and a cellular data plan are required. Networked Transport of RTCM via Internet Protocol (NTRIP) is a serviced provided across much of the world. HOW AN RTK AIRCRAFT DETERMINES POSITION with NTRIP: HOW AN RTK-CAPABLE AIRCRAFT CAPTURES POSITION with a BASE STATION: HOW A NON-RTK AIRCRAFT CAPTURES AERIAL POSITION: When this data is imported into a processing software such as Pix4DMapper, Leica Infinity, 3DR, etc, the data becomes “localized” and if all parameters are properly set, the localized data, in the form of an ortho, become measurable with a great degree of accuracy. These corrections, received during the flight, are written to the image metadata contained in each photo the aircraft captures. This allows the aircraft to know with much greater precision, where it sits in XYZ space as referenced to the ground locations. Construction surveys allow for a greater slide in precision vs land survey and this too is important to understand, while going beyond the scope of this article.Īn RTK aircraft receives “corrections” from a known grid system, via a couple of different technologies. Surveying creates an ortho-corrected, localized image or drawing of a ground area which contains measurable data with a highly accurate and precise measurability. The accuracy of measurements is affected by several factors, such as altitude of flight (ground sampling distance), size of image sensor, curvature of lens, latency of shutter to antenna, and other factors. Mapping with a UA system, creates a flattened, “localized” image of a ground area, that contains measurable data with some degree of measurability. How does this all work then? Why is it important?įirst, let’s define the differences between “Mapping” and “Surveying.” At a recent conference for example, a presenter claimed that with their dual RTK aircraft, they are capable of repeatable precision (accuracy) of less than 1/1000. Why does this matter? When discussing UA, it’s critical to know the level of precision the aircraft and accompanying system will provide. In AEC (Architecture, Engineering, Construction), an acceptable accuracy falls into “tenths” while Surveyors work in hundredths or thousandths.
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