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Running Head: Drone vs. RTK Page 1 of 22 Drone vs. RTK: Is There a Difference? Corey Albright Utah Valley University May 1, 2019 Course: Senior Capstone-SURV-49300-I01 Instructor: Danial L. Perry, MBA, PLS

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Running Head: Drone vs. RTK

Page 1 of 22

Drone vs. RTK: Is There a Difference?

Corey Albright

Utah Valley University May 1, 2019

Course: Senior Capstone-SURV-49300-I01 Instructor: Danial L. Perry, MBA, PLS

Running Head: Drone vs. RTK

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Table of Contents

Abstract ........................................................................................................................................................ 3

Background ................................................................................................................................................. 3

Methodology ................................................................................................................................................ 4

Location .................................................................................................................................................... 4

Materials ................................................................................................................................................... 4

Mission Planning ...................................................................................................................................... 4

Topographic Survey Workflow Using RTK ............................................................................................... 5

Topographic Survey Workflow Using a UAS ............................................................................................ 5

Comparison ................................................................................................................................................. 6

RTK GNSS .............................................................................................................................................. 6

Workflow ............................................................................................................................................... 7

Efficiency............................................................................................................................................... 7

Time ...................................................................................................................................................... 7

Accuracy ............................................................................................................................................... 7

UAS .......................................................................................................................................................... 7

Workflow ............................................................................................................................................... 7

Efficiency............................................................................................................................................... 8

Time ...................................................................................................................................................... 8

Accuracy ............................................................................................................................................... 8

Conclusion ................................................................................................................................................... 8

References .................................................................................................................................................... 9

APPENDIX A ............................................................................................................................................ 10

APPENDIX B ............................................................................................................................................ 11

APPENDIX C ............................................................................................................................................ 12

APPENDIX D ............................................................................................................................................ 13

APPENDIX E ............................................................................................................................................ 14

APPENDIX F ............................................................................................................................................ 15

APPENDIX G ............................................................................................................................................ 16

APPENDIX H ............................................................................................................................................ 17

APPENDIX I ............................................................................................................................................. 18

APPENDIX I ............................................................................................................................................. 19

APPENDIX I ............................................................................................................................................. 20

APPENDIX J ............................................................................................................................................. 21

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Abstract

With technology quickly advancing, people are able to perform tasks much faster and more efficiently than ever before. It seems that technology is advancing in every profession and land surveying is no exception. The introduction of GPS to land surveying roughly 20 years ago has made a huge impact in the industry. When they were first introduced, surveyors were hesitant to use them. Now today, almost every surveyor has a GNSS receiver and uses it daily. The same pattern can be seen with drones or UASs. Some surveyors are hesitant to start using drones in their surveys for some of the same reasons that were present with GPS—accuracy, time, cost, etc. On the other hand, surveyors have welcomed the new technology with open arms and are seeing great advantages of using drones. This project is intended to compare the difference between RTK GNSS surveying and UAS (drone) surveying. It is intended to show the pros and cons of both RTK and UAS surveying. By analyzing the workflow, accuracy, timetable, applications, and efficiency of both RTK and UAS, this project will show the land surveyor what will be most valuable to them in their practice.

Background

In 1993, President Clinton made GPS available to public by stopping the scrambling of the GPS signal. When the GPS signal became public, few people jumped on board. GPS receivers were costly and they were huge compared to today’s receivers. It wasn’t until the 2000s, that GPS receivers were becoming more advanced. They were also becoming cheaper. With the cost and size of receivers dropping, they become more appealing to land surveyors. Receivers have advanced to even being able to connect to other countries’ satellites making them even more reliable in terms of connectivity. Because of this “GPS receivers” are now being called “GNSS receivers.” GNSS receivers have become one of the main tools of surveyors today. They are relatively cheap, they are fast and they can eliminate multi-person survey crews allowing more technicians to be in the field at once. It’s hard to imagine surveying without GNSS receivers. Within the last ten years drones or unmanned aerial systems (UAS) have gained popularity among the public. UAS have many applications. They are used recreationally for aerial photos of landscapes or events, real estate, package delivery and now they are being introduced into land surveying. Much like when the GPS receiver was first introduced into land surveying, some surveyors are hesitant to utilize this new technology. Why would there be hesitation for something that could make a surveyor’s job possibly easier? Some possibilities that some surveyors say are UAS are still new and there are still bugs, UAS aren’t as accurate as an RTK GNSS receiver, the image processing takes too long, or jobs may be too small for a UAS. This is not an inclusive list of all the reasons, but just some examples. For this project, a typical topographic survey was performed on a parcel of land measuring 20 acres. It was surveyed once using an RTK GNSS receiver and once using an UAS. An RTK GNSS receiver was used in conjunction with the UAS only to set ground control points (GCPs). This is typical of a drone survey. Once the data was collected, the typical workflow was used to produce a deliverable for each piece of equipment. For the GNSS receiver topographic survey, AutoCad Civil3D was used to import points, create a surface, and produce a final map. For the UAS, Pix4DMapper was used to import GCPs and stitch the images together to create a DTM and orthomosaic. AutoCad Civil 3D was used to create a final map. Each process was carefully analyzed for time, workflow, accuracies and efficiency.

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Methodology

Location

To begin this project, a suitable plot of land had to be selected to perform the survey on. To obtain results that would mimic a “real world” situation, the piece of land had to be big enough to be flown by drone, but reasonable enough to walk the entire piece. The parcel of land also had to be free of overhead obstructions, mostly open, and few people. Google Earth was used to search for different, suitable spots. Two different spots were chosen to investigate. One was at Chicken Creek near Strawberry Reservoir (Appendix A) and the other was located along the Provo Bench in South Provo, Utah (Appendix B). With a heavy snow year, it was quickly determined that Chicken Creek would be unfeasible. Provo Bench was investigated next, only to find power lines running parallel to the entire bench. It was decided that a new location must be selected. The third location to be investigated was at West Mountain, near Payson, Utah (Appendix C). The parcel of land met all the requirements that were decided upon and was determined to be the location of the project site. There were few trees, few people, and it was a large, wide open space. This is the site that became the project location. Materials The main materials necessary for the project included an RTK GNSS receiver, a UAS, and aerial targets to record as ground control points (GCP). Other materials included spray paint (for painting check point targets) and lath (to visually mark check points on the ground). The project also required materials for use on the office side. A drafting program and processing program would be needed. The GNSS receiver used for this project was a Trimble R10 along with the TSC3 controller. The UAS used was the DJI Phantom 4 Pro. For the aerial targets I used custom 18’x18” targets designed by Dan Perry from Utah Valley University (Appendix D). As stated above, the drafting program used was AutoCad Civil 3D and to process the images, I used Pix4D Mapper. Once I knew I had the materials secured that I needed, I could start planning my topo project. Mission Planning After the determination of a jobsite, I could begin designing where I wanted to layout my parcel of land. Utah has a great resource for geographic information called the AGRC (Automated Geographic Reference Center). Information for anything geographically related in Utah can be found on their site at www.gis.utah.gov. For my project site, I was able to download aerial imagery and georeference it in AutoCad Civil 3D. Once the images were georeferenced in Civil 3D, I could draw a 20 acre boundary where I wanted my parcel of land to be (Appendix E). I wanted to include some sort of feature as opposed to just a flat piece of land to really test how well a UAS could pick up on features. There was a ravine in the middle of the parcel of land that would help to accomplish this goal. Points were set at each of the corners and were imported into the data collector of the R10. By doing this, I would be able to go to the location and set my site corners. This would aid in data collection within the desired boundary. Section corners of the surrounding section were also researched so they could be tied into as control for the project. The Utah County Surveyor’s website contained tie sheets to said section corners. These tie sheets included the position of the section monument.

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Topographic Survey Workflow Using RTK Once mission planning was complete, the topographic survey of the parcel of land could be completed. Part of this project was to determine the time it takes to perform each form of a topographic survey. Upon arrival at the selected location, time began being recorded. The first step for the RTK topo survey was to tie into the researched control—the section corners. Once the section corners were tied into and I knew that my GNSS receiver was working properly, I could begin the topographic survey. I began by setting the property corners so I could visually see where my desired property was. This way I knew for certain, that I was obtaining topogrpahical data within my parcel boundary. I also collected data within an approximate fifty foot border. With the parcel boundary setup, I could then begin gathering topographical data. A fifty foot grid was used to walk the parcel of land collecting data. Cross sections of the ravine were taken to later detail the topography of it. The issue that I continued to have using Network RTK was the continued loss of connection. Stopping to recconnect slowed down the job enough to where I was forced to use a hotspot from my phone. When I connected the GNSS to my phone, I had no connection loss and was able to finsih the job. Unfortunately, this scenario happens on actual job sites and because it does, I included it into my final time. The amount of time it took from when I arrived at the location to when I left was approximately 10 hours. That includes checking control, the actual topo and detailing, handling network loss, and breaking down the equipment. The other half of a topographic survey is the office side. This is the side that leads to what a client wants to see. I began my office work by opening the .csv file that was created and cleaning it up. There were some bad shots that needed to be deleted. There were also typos in description codes and point numbers that needed to be fixed. These are things that are common in the practice. With a clean .csv file, it is much easier to work with in Civil 3D. Now that I had a clean .csv, I could import my points into Civil 3D and begin my drafting work. Including the control shots with all of the topo shots, my point file contained 368 points. Using those points, I generated 10 foot contours. There was a dirt access road that ran through my property that drafted as well. I did not shoot any of the trees out there so I had to rely on approximation from the above mentioned aerial images obtained from AGRC. A final topographic map was made using a title block and is sufficient enough to give to a client if this were for an actual client (Appendix F). With everything involved in the office side of a topographic survey by RTK, it took approximately 11 hours to create a satisfactory deliverable. Topographic Survey Workflow Using a UAS In order to obtain precise results from a UAS, a GNSS receiver is required to shoot ground control points (GCPs). Without GCPs, the final image will be in an arbitrary coordinate system and can only be used for a nice picture. With that said, I began the UAS topographic survey by checking into the determined section corners to check my control. I could then begin setting my GCPs once I knew that my control was good. To begin an aerial survey, GCPs must first be laid out and shot with the GNSS. An aerial survey usually requires a minimum of 3-5 GCPs. For this project, 20 GCPs were set. Each target had a number on it so that when it came time to select the GCPs during processing, I would know which GCP corresponded to which coordinate that was recorded. Since this project is testing the accuracies of a UAS, among other things, I needed to set check points that I could later check into during processing to see how accurate my flight was. To do this, 50 X’s were painted on the ground and labeled with a corresponding number, 1-50. I then took a GNSS shot on them to later check them in Pix4D. After all the GCPs and check points were set out and occupied, the parcel of land was ready to be flown. A setup is required in the controller to determine a flight path, sidelap and endlap, and the flying height. A sidelap of 80% and a front lap of 70% were used. The flying height used was 150 feet. Once all the parameters are set, the UAS is ready to take off. My flight took approximately 30 minutes, which required a battery change in

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between. For the 30 minutes, all that was required was to watch the UAS and make sure it was flying the correct path, make sure it was not interfering with any object, and be certain that it was not malfunctioning. The only thing left to do after it was done flying, was to pick up the GCPs. With the setup of all the GCPs (I am not including check points since in a normal situation, they wouldn’t be necessary), data collection, and cleanup, it took approximately 5 hours in the field. The beginning and ending of the office work of a UAS and GNSS are very similar. I first needed to open the .csv file and remove the bad shots, as well as the typos. Again, this will aid in a more smooth input into Pix4D. I also checked my images to make sure all of my images were clean and usable. The first step in Pix4D, is to import the geotagged images from the UAS. In this case, I had 772 images. From this point, an initial process can be run or GCP coordinates can be imported to better improve the location of the image. For the purpose of this experiment, I ran the initial process without selecting any of the GCPs that I had coordinates for. With the computer I used, (Appendix G) the processing took 15 hours. After the initial processing is done, an image is shown of the project. I then imported my GCPs to see the error. After selecting the GCPs, I had an error of consistently 40 feet horizontally. In Pix4D, there is an option to “reoptimize” the photo using the GCPs. After running, “reoptimize” my computed GCPs were still about a foot off from the actual, GNSS recorded points. I decided to re-run the initial process with my selected GCPs and check points. By re-running the initial process, it yielded much better results. Out of my 20 GCPs and 50 check points, only 14 GCPs were usable and 49 check points. Most of the differences between the actual, GNSS location of the GCPS and the Pix4D computed location of the GCPS were 0.1 foot or less horizontally. I wasn’t very concerned about vertical positions being over 0.1 foot since GNSS isn’t great with vertical, but the highest elevation difference wasn’t even over 0.5 foot. With the location of the project being precise, I processed a DTM (which included 10 foot contours) and an orthomosaic. With a ground sampling distance of 1.2307 cm/pixel, I was able to produce a fairly precise orthomosaic and DTM. The generated DTM and orthomosaic by Pix4D can be imported into Civil 3D. The DTM is saved as a .dxf file and the orthomosaic is saved as a .tif file. Using those files, a final topographic map was then created for the UAS survey. Typical work practices were used for drafting, including, linework, labeling, and title block. After all drafting was complete a final deliverable was created that would be suitable to give to client (Appendix H). The time it took to complete all office time for the UAS survey was 26 hours (11 hours drafting and pre-processing, 15 hours processing).

Comparison

Each method (GNSS and UAS) for performing a topographic survey will have their own pros and cons. The main objective of this project was to see what differences there were between them, which includes workflow, efficiency, time, and accuracy. RTK GNSS From the research and experiment that was conducted, these are the conclusions that I gathered from using the RTK GNSS to perform a topographic survey.

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Workflow The workflow of the RTK GNSS is one that many surveyors are familiar with and are very good at doing it. It is smooth and straight forward. The surveyor goes out to the jobsite and collects the points, drafts, and then there is the deliverable. There is no waiting around for processing of images. Efficiency The efficiency of a surveyor using an RTK GNSS could probably be debated. When a surveyor is physically on the ground, there is a lot of walking that needs to be done. Especially in this project since it was 20 acres. Walking a 20-acre piece of land on a 50-foot grid will take a full day. But with walking, comes the benefit of seeing everything that is on the ground. That means more detail for the survey. If this were a small piece of land, it may be more efficient for the surveyor using the RTK since there is less setup. Upon arrival at the jobsite, the surveyor could be setup, connected, and collecting data in 15 minutes or less. Whereas, a UAS would require setting and occupying GCPs, flight time, and retrieving the physical GCPs. Time Time can go hand in hand with efficiency. For this project the office time for the RTK GNSS and the UAS were identical at 11 hours (subtracting processing). The time out in the field for the RTK GNSS was double the amount of time of the UAS—10 hours.

Accuracy Depending on the accuracy being looked at, the RTK GNSS could be considered more “accurate.” The reason being is with the GNSS, more detail can be obtained. Man-made features on a project such as manholes, fences, building corners, and roads can all be tied down very precisely with a GNSS. Features like this can be missed when using UAS. If we look at the number side of the accuracies, as long as a UAS is paired with a GNSS, the numbers are very comparable. UAS From the research and experiment that was conducted, these are the conclusions that I gathered from using the UAS to perform a topographic survey. Workflow The workflow of the UAS took slightly longer than the GNSS. With the UAS, it involves setting out GCPs and shooting points for those GCPs. Then there is the flight and cleanup. When the data is brought back to the office, it can’t be drawn right away. The images have to be processed. In order to process the images correctly, the GCPs have to be manually selected. After everything is set up then the processing could take up to 15 hours. This all needs to be done before the actual drafting can start. With all the processing, though, comes some neat things. With UAS images, an orthomosaic can be produced. It will be the most current image of the site. Point clouds and DTMs can also be produced from the images and can be used to measure three dimensionally off of. These are things that cannot be done with the GNSS. The plus side of this workflow is that the processing can be done overnight so the next day, drafting can begin.

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Efficiency The field work of the UAS was very efficient compared to the GNSS. Once everything was setup, the actual flight of the UAS was very quick and efficient. As mentioned above, the flight only took about 30 minutes for the whole 20 acres of land. With a piece of land as big as this project, the UAS would be very efficient in the amount of work that could get done in a short amount of time. Time As mentioned under the GNSS, time and efficiency seem to go hand in hand. The amount of time it took to fly this whole project was half the time of the GNSS. If the processing were to be cut out due to having it process overnight then the total time of the projects would be very comparable. The total project time for the GNSS was 21 hours. The total project time for the UAS was 31 hours (subtracting the processing time). That’s a difference of 10 hours. Accuracy The accuracy of the drone can be dependent on a few different things, such as, camera specs, side/front lap, or flying height. One of the biggest items that I found in this project was tying down the GCPs correctly. When the GCPs were used and tied correctly, the accuracy differences were very minimal (Appendix I).

Conclusion

Drone vs. RTK: Is there a difference? Well yes there is a difference and there are similarities too (Appendix J). There isn’t a solid answer to which one is better, though. It really depends on what the project is and what kind of surveyor you are. The UAS can obtain similar accuracies to the RTK GNSS, but it may not always be the best tool for the job. In highly populated areas where great detail is involved, a GNSS would probably be a better tool to use. For large, open areas where there isn’t much detail, then a UAS might be the better option. The option to choose one over the other also depends on the surveyor. Some surveyors wouldn’t mind hiking all day up and down hills and ravines, whereas, others would dread that. If a UAS can fly it for them in half the amount of time and half the amount of walking then they would prefer that. Even if a surveyor doesn’t want to use the UAS for a topo, they could use it to search for evidence of monuments or even just to get a current image of the jobsite. I don’t believe a UAS will ever replace a GNSS. UASs are another tool to add in the toolbox of powerful tools that surveyors have available to them.

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References

Barry, P., & Coakley, R. (2013). Accuracy of UAV Photogrammetry Compared with Network RTK GPS. Cork, Ireland: Baseline Surveys, Ltd.

Devriendt, L., & Bonne, J. (2014). UAS Mapping as an alternative for land surveying techniques? The

International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 39-45.

Henning, W. (2006). The New RTK: Changing Technologies for GPS Surveying in the USA. Surveying

and Land Information Science, 107-10.

Up in the Air. (2013, October). Point of Beginning, pp. 20-21.

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APPENDIX A

Figure 1 Chicken Creek, near Strawberry Reservoir

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APPENDIX B

Figure 2 Provo Bench, South Provo, Utah

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APPENDIX C

Figure 3 West Mountain, near Payson, Utah

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Figure 4 Custom 18"x18" Targets

APPENDIX D

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APPENDIX E

Figure 5 20 Acre Boundary

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APPENDIX F

Figure 6 Final Topographic Map for GNSS

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APPENDIX G

Figure 7 Computer Specs

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APPENDIX H

Figure 8 Final Topographic Map for UAS

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APPENDIX I

POINT NAME ERROR (N) ERROR (E) ERROR (Z) 3001 0.018 -0.058 0.003 3002 <Null> <Null> <Null> 3003 0.048 0.039 -0.04 3004 0.032 0.005 -0.03 3006 -0.052 0.038 0.094 3005 0.032 -0.011 0.026 3007 -0.029 -0.043 -0.01 3008 -0.025 -0.01 -0.033 3009 -0.016 -0.024 -0.11 3010 0.02 0.014 -0.099 3011 -0.033 0.066 0.013 3012 -0.017 -0.059 -0.054 3013 -0.02 0.018 0.052 3014 <Null> <Null> <Null> 3015 -0.01 0.016 0.039 3016 0.033 -0.022 0.033 3017 <Null> <Null> <Null> 3018 <Null> <Null> <Null> 3019 <Null> <Null> <Null> 3020 -0.001 0.035 0.181

Mean (ft) -0.001299 0.000313 0.004401 Sigma (ft) 0.028712 0.035917 0.071166

RMS Error (ft) 0.028742 0.035918 0.071302 Figure 9 Error Differences (GCPs)

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APPENDIX I

POINT NAME ERROR (N) ERROR (E) ERROR (Z) 5001 -0.083 0.07 0.372 5002 -0.041 0.047 -0.355 5003 -0.058 -0.014 -0.147 5004 -0.025 -0.035 -0.07 5006 -0.019 -0.001 -0.261 5007 -0.046 -0.009 -0.151 5008 -0.011 0.018 0.079 5009 -0.035 0.002 -0.174 5010 0.002 0.019 0.228 5011 0.003 -0.014 -0.024 5012 0.077 0.058 0.075 5013 0.063 -0.019 0.048 5014 0.028 -0.012 0.062 5016 -0.027 0.005 0.037 5017 0.015 0.097 0.247 5018 -0.005 -0.068 -0.197 5019 0.008 -0.012 0.05 5020 0.017 0.034 -0.069 5022 0.044 0.019 -0.123 5023 -0.019 0.007 0.013 5024 -0.074 0.061 0.057 5025 <Null> <Null> <Null> 5026 -0.158 0.053 0.283 5027 -0.047 0.085 0.01

Figure 10 Error Differences (check points)

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APPENDIX I

5028 -0.045 0.107 0.009 5029 0.01 0.003 -0.007 5030 -0.072 0.071 0.218 5031 -0.039 0.068 0.308 5032 -0.041 0 -0.012 5033 -0.015 0.063 0.141 5034 -0.018 0.005 -0.023 5035 -0.015 0.067 -0.026 5036 -0.023 0.009 -0.172 5038 0.059 -0.054 0.012 5039 0.032 -0.034 -0.34 5040 0.002 0.03 -0.038 5041 0.015 0.092 -0.292 5042 -0.06 0.082 0.281 5043 -0.075 0.123 0.472 5044 -0.031 0.099 0.371 5045 0.033 0.11 0.247 5046 -0.068 0.098 0.213 5047 -0.061 0.166 0.303 5048 -0.081 0.199 0.241

5049_1 -0.139 0.108 0.07 5049 -0.146 0.164 0.155 5050 -0.112 0.036 0.077

Mean (ft) 0.027341 -0.0452583 -0.046727 Sigma (ft) 0.051508 0.058497 0.190873

RMS Error (ft) 0.058314 0.072355 0.19651

Figure 11 Error Differences (check points) cont.

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APPENDIX J

Figure 12 RTK GNSS Topo

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APPENDIX J

Figure 13 UAS Topo