RTK and Drone Mapping: Do You Want It? Is It Value It?

Actual-Time Kinematic (RTK) is a buzz time period within the UA business, one many pilots could not perceive, although they could be “mapping” with an uncrewed plane (drone).   In relation to RTK and drone mapping, how vital is the expertise to a drone providers supplier?  Will it earn a providers supplier extra money?

The next is a visitor submit by drone business veteran Douglas Noticed Eagle, Manufacturing and Schooling Director at Sundance Media Group.  DRONELIFE neither accepts nor makes fee for visitor posts.

All pictures courtesy Sundance Media Group, used with permission.

When a producer supplies RTK functionality, some really feel they’ve achieved nirvana, and are prepared to start out a drone surveying enterprise, however…

Not so quick there, pardner. There’s a important distinction between proudly owning an RTK plane and being a surveyor. A surveying diploma is at minimal, 4 years of college and relying on the world of curiosity, as much as six years of college plus time within the area, plus passing the land surveying exams will enable a person to achieve a license to survey.

As UA grows in recognition, tight accuracy and precision have gotten extra attainable. It’s additionally vital to understand that there are completely different levels of accuracy which are thought-about “survey grade” and the time period “survey” has very completely different meanings in varied endeavors.

In AEC (Structure, Engineering, Development), an appropriate accuracy falls into “tenths” whereas Surveyors work in hundredths or thousandths.

Why does this matter? When discussing UA, it’s crucial to know the extent of precision the plane and accompanying system will present. At a current convention for instance, a presenter claimed that with their twin RTK plane, they’re able to repeatable precision (accuracy) of lower than 1/1000. That is extremely doubtful.

How does this all work then? Why is it vital?

First, let’s outline the variations between “Mapping” and “Surveying.”

Mapping with a UA system, creates a flattened, “localized” picture of a floor space, that accommodates measurable knowledge with a point of measurability. The accuracy of measurements is affected by a number of components, resembling altitude of flight (floor sampling distance), dimension of picture sensor, curvature of lens, latency of shutter to antenna, and different components.

Surveying creates an ortho-corrected, localized picture or drawing of a floor space which accommodates measurable knowledge with a extremely correct and exact measurability.  Development surveys enable for a larger slide in precision vs land survey and this too is vital to grasp, whereas going past the scope of this text.

An RTK plane receives “corrections” from a recognized grid system, by way of a few completely different applied sciences.  This permits the plane to know with a lot larger precision, the place it sits in XYZ area as referenced to the bottom areas. These corrections, acquired in the course of the flight, are written to the picture metadata contained in every picture the plane captures.  When this knowledge is imported right into a processing software program resembling Pix4DMapper, Leica Infinity, 3DR, and so on, the info turns into “localized” and if all parameters are correctly set, the localized knowledge, within the type of an ortho, grow to be measurable with an awesome diploma of accuracy.

 

HOW A NON-RTK AIRCRAFT CAPTURES AERIAL POSITION:

 

 

HOW AN RTK-CAPABLE AIRCRAFT CAPTURES POSITION with a BASE STATION:

 

HOW AN RTK AIRCRAFT DETERMINES POSITION with NTRIP:

 

Networked Transport of RTCM by way of Web Protocol (NTRIP) is a serviced supplied throughout a lot of the world. With the intention to use the sort of correction, a mobile modem, a receiver able to RTK correction and a mobile knowledge plan are required.  Some areas present the NTRIP knowledge connection without charge (often via a State or municipal service) or for a nominal, usually annual, payment. NTRIP knowledge is transmitted by way of RTCM, which carries the correctional data. The NTRIP server is in fixed contact with GNSS nodes surrounding many areas of the USA. This server consistently broadcasts GPS knowledge by way of wifi, and is used to offer wi-fi transmission of location knowledge to many various industries. For instance, NTRIP is closely utilized by agriculture, driverless vehicles, space stock administration, surveyors, engineers, departments of transportation.

The NTRIP nodes/stations are fastened at recognized positions, and are consistently receiving satellite tv for pc location knowledge. The collective nodes feed a server, which aggregates the situation knowledge between the nodes and satellites, and sends out a correctional knowledge stream, informing a “rover” machine of it’s precise location in XYZ area. It is rather, very correct, offering functionality of 1cm (.39”) in horizontal and 1.5cm in vertical precision. That is ok for many types of aerial precision work.

HOW DO WE MEASURE ACCURACY?

Initially, we want a recognized level, if we’re utilizing solely UA and a Base station or NTRIP corrections system.

These could be captured utilizing a wide range of GPS programs, such because the DT Analysis 301 (pictured right here), with a rod and bi-pole over a Hoodman Floor Management Level system, or maybe one thing extra elaborate resembling a Leica GS18 receiver or a extra reasonably priced, but much less versatile Emlid RS2 Base/Rover system. The Floor Management Factors (controls), could also be cellular, or could also be painted on the bottom as seen beneath. That is extra frequent; a particular nail that has grids or a detented level for precision, is pushed into the bottom and spray paint marks the world. Paint could also be utilized to quickly discover the nail whereas strolling or flying.  That is particular surveyor paint, which may be bought at most any survey provide (often in instances of 12 cans).

The recognized level (also called a “verify”), is to be in comparison with the info supplied by the UA as relative to that recognized level. The distinction marks our ellipsis of error. Instruments resembling Leica Infinity, Pix4D, and related are capable of exhibit the variations in location. Typically, the plane knowledge needs to be inside 1-2 cm of the recognized level captured from a static place.

Typically, these recognized checkpoints could also be accessed by way of a county or state system, the place recognized monument factors set by an expert land surveyor have been recorded.

ONCE THESE PARAMETERS ARE MET….

Precision can happen.

Let’s take a look at varied examples of accuracy and precision.

First, we’ve obtained a picture captured from a UA flying at 75’ in altitude, no correction community, projecting the place it will likely be when locked to floor (localized) and the way correct to place it’s. This accuracy is just barely larger than the accuracy of a cellular phone GPS system (not very correct).

 

On this picture, the projected level is almost 10’ off from the precise level (captured with a Leica GS18i). This degree of accuracy isn’t very helpful in any type of building nor survey setting. That is captured by way of autonomous flight, in comparison with a static place with the Leica GS18i. The UA has no RTK functionality. That is the extent of accuracy a typical UA will present, relying on sensor dimension, velocity, and altitude.

On this picture, we see the projected level is far nearer to the precise level, as an RTK antenna system with no corrections (NTRIP or Base Station) utilized in flight. The projected and precise distinction is eighteen.5”.  Shut, however not shut sufficient for many sorts of labor.

Final, we are able to see what happens when an NTRIP or Base Station are utilized in flight.

On this situation, the precise and projected factors are offset by roughly 1cm. This degree of accuracy is required for many business functions. This picture was captured with an Autel EVO II RTK plane corrected by way of NTRIP community, processed in Pix4DMapper utilizing checkpoints.

CAN I MAKE MORE MONEY WITH AN RTK DRONE, BASE STATION, and NTRIP?

Typically talking, sure. Pilots want to grasp and have expertise with rather more than merely programming an automatic mission and capturing nadir pictures so as to be a profit to a survey firm, no matter whether or not it’s survey for building, ALTAs, or land.  The worth (what you cost) relies on the period of time, enchancment on knowledge demonstration, and different advantages the UA brings.

HOW DO I KNOW MY COORDINATES AND SCALE ARE ACCURATE?

That is the place the maths and understanding of coordinates are required. Totally different corporations could have varied technique of figuring out localized “fact.” Some are very regimented, whereas others are casual and should contain just a few checkpoints. The American Society for Photogrammetry and Distant Sensing  (ASPRS) presents tips on verification of accuracy, most of that are past the technique of a typical UA pilot and their tools.

Key parts of ASPRS Positional Accuracy Requirements  

• Accuracy is measured by the RMSE (Root Imply Squared Error) of the distinction between modeled factors and independently measured factors.
• Accuracy can solely be precisely measured utilizing Checkpoints that weren’t included within the manufacturing of the mannequin.
• Floor measurements have to be made with an impartial supply of upper accuracy than the aerial mapping system.
• Horizontal and Vertical accuracy needs to be measured independently, and may have completely different properties relying on vegetation.

SO, IF I HAVE AN RTK AIRCRAFT AND ITS VERY PRECISE, WHY CAN’T I BE A SURVEYOR IN MOST STATES?

Most states require licensure from an accredited testing system/program. Licensure candidates usually should cross the Fundamentals of Surveying (FS) examination, the Ideas and Apply of Surveying (PS) examination, and a state-specific examination. Examine along with your state licensing board for state-specific examination data and necessities. A number of states require solely a highschool diploma along with testing.

IF I CAN’T BE A SURVEYOR, WHY USE AN RTK SYSTEM?

Whether or not you’re a surveyor, contractor, or UA pilot on the lookout for alternatives to work with UA in precision-focused environments. RTK workflows present exact knowledge when correctly managed and utilized. It is a profit to anybody utilizing any type of mapping whether or not it’s DTM, DEM, Contours, or a easy ortho. Realizing the info has been localized and to scale is vital to anybody offering measurements, whether or not for accident scene reconstruction in public security, or for figuring out boundaries and corners for land improvement.

Learn extra about RTK mapping:

 

Douglas Noticed Eagle is the Founder and Director of Academic Programming at Sundance Media Group.  SMG serves as a guide throughout the sUAS business, providing coaching and talking engagements on sUAS matters: UAV cinematography, business and infrastructural sUAS functions, sUAS threat administration, night time UAV flight, aerial safety programs, and 107 coaching.