For this article I will go through the evolution of the way things were to the way they are today when working with local coordinates. The information is presented as fundamentals to your understanding of how GPS works on a jobsite. Not being familiar with these concepts could cause issues along the way as you work through working with local coordinates.
Talking Survey Coordinates
When performing a layout and surveying with a total station, level, chain, or a combination – equipment jobs are assigned coordinates based on a random northing and easting. For smaller sites, it seems the most common starting coordinate is 5000, 5000. The “bottom, left corner” would be the starting location of the assumed coordinate system so the numbers going to the north and east would get bigger. This also leaves room to the south and west of the start point to avoid negative coordinates – more on that later.
In the past, points that were to be laid out on a job were assigned coordinates that conformed to where the arbitrary coordinates started. This system works well, but we haven’t used it in years. Almost all our GPS based jobs are located on state plane coordinates. Later in this offering I will talk about the mechanics of a localization or calibration. It’s the same thing but different names depending on the brand of equipment you use.
In the early days of GPS survey, localization was carried out by aligning GPS coordinates with the local grid assigned usually during the initial survey. Things worked well and the equipment wasn’t confused by the numbers. Somewhere along the way, people realized that their data could be monetized if it could be placed on a map in the correct location. A surveyor working in a town or city could use the control from surrounding jobs to locate control for a new job. That information would be worth money to both the city and GIS providers to enhance location services.
The shift to map coordinates was not immediate. One of the reasons was surveyors did not want their control being used for a neighboring job that they were not being paid for. Many also stated the additional liability of somebody using their state plane points and then something going wrong. It may not be their problem but that would be decided by lawyers, so it was best avoided.
Localization and Calibration
Autonomous GPS receivers used in cars and hiking units are incredible. We can geolocate within a few feet. This was not always the case. Selective Availability (SA) was an intentional degradation of public GPS signals implemented for national security reasons. In May 2000, the U.S government discontinued its use of Selective Availability to make GPS more responsive to civil and commercial users worldwide. When SA was in use, the best autonomous units could achieve was 50–100-foot accuracies. Great for travel or hiking, not so much for precision. Without doing a deep dive, we employed a base station to triangulate signal locations to give us the accuracy we see today.
How do we get the GPS to see us in state plane coordinates? A localization is required to sync these two different measurements. What you are doing is telling the GPS, “When I am at this Latitude, Longitude, and GPS height, tell me I am at this northing, easting, and elevation.” There are a couple of things to note in this statement:
- Latitudes, longitudes, and height are what the GPS is reading all the time. Our screen shows the coordinates we want it to.
- The units all use meters in the background, converting them to decimal feet at the end for viewing on the screen.
- It is important to note that I used the word “height” when talking GPS and elevation with state plane coordinates. GPS uses a mathematical ellipse to establish the not regular sea level. Your elevation will always be different, sometimes over 100 feet. Be sure you are talking about the correct type of tall.
Above is a shot of a few lines of a site calibration. This is the Trimble data collector file, (.dc)
- The origin Lat/North are in the first two rows. This is how we tell the GPS to give us desired coordinates for latitudes and longitudes.
- The horizontal adjustment is needed to force the points to match up. The translation and rotation of the points will usually never be an issue to you. When things do not work right, then you get deep into this data.
- Scale factor is usually the only thing you need to pay attention to. If you have a 1 followed by four zeros or four 9’s following a decimal point, then you should be good.
- The GPS must be mathematic, just like the ellipsoid used for mean sea level, your job gets tilted on an inclined plane.
- The vertical adjustment shows the slopes to the north and east from an origin point in parts per million. In this case, the slope to the east is .000058%. This is the reason you need to have multiple calibrations on longer jobs. In one mile, the vertical on this job could be off by three tenths.
Here is a control file from a Topcon controller. I drilled down to control point 120 and was given the following information:
- The northing, easting and elevation of the point are either keyed in manually or imported from a text file.
- Upon occupying the point, the relationship is made.
- The residual values, (accuracy) are within my desired tolerance so I checked both the vertical and horizontal use in the control calculations for this point.
- Note the almost 70-foot difference in the local elevation and the GPS height.
Things do not always go according to plan. When something does not look right, it is probably wrong.
US and International feet
A source of confusion and sometimes great expense is that in the United States we use two different measurements for a foot. The difference is 2-feet per million feet. The problem is that state plane coordinated can be in the millions so a mix-up can put you several feet from your intended target. Six states use the international foot with the balance using U.S. feet.
States using International Measurement are:
- North Dakota
- South Carolina
To make things even more complicated, the U.S. foot will be deprecated as of January 1, 2023 making the international foot the standard. There is a lot of commotion going on around the proposed change and as far as I can tell, it will happen. The biggest argument is that a majority of people and real estate use the U.S. foot, why not change to that? Time will tell, stay tuned.
A fun website
To help you navigate to any place on earth (and your big jobsite) easily, I have been using an app called What 3 Words, https://what3words.com. The world is now broken down into 3-meter squares. This has really helped emergency services as well as friends who can never quite get directions right. We use it in the field to tell people where we are meeting. It sure beats “go to the job trailer and keep driving.”
Over the past 15 years we have had to sort through different types of 3D data for a job. In this presentation, I will go over some issues we find when dealing specifically with roadway rehabilitation. Issues can come up with any type of construction data. However, roadways are more critical. Maintaining traffic and smoothness requires higher precision than a new parking lot for a retail site.
The major interstates are in place, but in different areas they are getting widened and constantly repaired. Larger arterial roads get re-routed and widened as population changes occur. These and other factors mean that you need to be efficient at this type of work as there is a lot of it out there.
In our hypothetical case, we are milling, filling, and widening a road section. Here are the various types of data you could receive for existing conditions on a job.
GPS Rover Shots
The project has been worked on for a while and uses GPS to get things organized. The job is calibrated, and work has been done in the field. Some topo shots have been taken of the edge of pavement, so the new lanes have a vertical to attach to. The main issue here is the quality of the data.
- How good is the calibration?
- Did the operator check the known control?
- How long was the point occupied? In heavy highway work, long observations are dangerous.
- Was the pole plumb?
- How recently was the rover pole calibrated?
There is no way to know this information by reviewing the metadata of a shot or a session. No assumptions can be made regarding quality. Hopefully, there is an opportunity to make a surface of the data to check accuracy. Yes, there can be issues with the GPS performing the check. Where precision is an issue, I do not fully support GPS only information.
GPS information gets used a lot, and we work with it all the time. No need to stop trusting GPS rover data. You do need to be aware of the problems you may encounter when counting on it for high precision. Fully trusting GPS data for a highway reconstruction will most likely not get a rideability bonus.
I have been doing topo work with drones since the infancy of using drones to collect data. Drones are a great tool but must be used properly. In addition, expectations must be managed to provide accurate information within tolerance.
The best accuracy one should expect from a drone topo is a half a tenth (.05’). That is great news for doing interim dirt topo(s) and pre-job topo(s) on mostly cleared land. Photogrammetry software does not perform well with a single-color surface. We often have problems with sand and dirt work that is smooth and monotone. White and asphalt paving both have the same issue. It is difficult to get any consistency with photogrammetry on these surfaces. Things get worse when you try and extract curb data, elevations jump. Photogrammetry cannot be used to obtain paving elevations for rehabilitation and widening.
Over the years we have provided drone topo(s) on heavy highway projects. That information is used as part of a hybrid surface. The drone is great for slopes and median while a higher accuracy method is employed for paving areas.
I am excited about the use of drones for LIDAR (Light Detection and Ranging, 3D Laser Scanning). We have relied on full scale aircraft mounted LIDAR for years and are happy with the results. The problem with drones and LIDAR is vibration. The measurement is taken and by the time the unit gets a return, the vibration has put the unit in a different location. Yes, the change is small but enough to cause inaccuracies that are being improved upon every day. I have visited some white papers on new offerings and am confident the issue will be sorted soon. I feel within a year, the process will be accurate and repeatable. Within five years of that prices will drop so this will become the norm.
Many of us have seen mobile LIDAR units at tradeshows. The late model SUV with a GPS antenna and a big scanner mounted on top is impressive and expensive. I get a lot of calls and emails on this topic, and the manufacturers know this needs to be solved.
Mobile LIDAR is a great solution, but the issue is in the cost. Figures can vary based on options and software but $750,000.00 is a good estimate all in. That’s too much money for a contractor, so leaving it to survey and mapping companies is a better option. I have consulted with numerous firms considering the purchase of this equipment. Here are the facts.
- It is expensive.
- There is a steep learning curve.
- People will need to be hired to operate and maintain the gear and vehicle. Usually two expensive office/field operators.
- To gather and process the huge amounts of data collected, you will need:
- Expensive field laptops
- A lot of solid state portable hard drives. This data is easier to express mail than upload in many cases.
- An office computer(s) to do initial processing and reduction to specified densities. This takes a long time and can use up to three powerful desktop units to keep various jobs on schedule.
- Finding people to buy data. This unit needs to be moving all the time. The crew will be on the road a lot. Depending on population density, a 500-mile radius may be needed to make this profitable.
As you can see, quality data comes at a cost. When hiring the service to be done for you, expect from 4-10 thousand dollars a mile depending on the job and distance from the unit’s home base as well as the project size.
Ground Based LIDAR
Currently, the use of this technology is striking the balance between accuracy and cost, and it comes with a price. Ground based LIDAR can be as accurate as necessary for paving work. As with any technology, especially one we are expecting high precision, conditions need to be met.
- The job needs to be localized and the quality of that must be verified. LIDAR needs to be setup over known points. This is not necessary for all scans, as they will register to each other. On any linear project like a roadway, there needs to be a high number of good control points for verification and setup.
- Operator error is the main issue we see for poor data. It is easy to use but setup and operation are procedural. If one step is missed in the process the data quality will suffer.
- These instruments are sensitive and need to be handled carefully. If a drop or a fall happens and the unit is not checked, data quality can suffer.
- Training is not too difficult. One person can do the work and needs to be responsible for the unit.
- Prices are dropping to the point where a contractor can pay for a unit with the profit from a job or two. Rental is an option as the dealers know you need it and may not want to purchase.
- File sizes are going to be big, so be prepared for a lot of storage space.
- Scan only what is needed. We see a lot of scans including trees. We are doing roads, not lumber.
Disclaimer: This article does not contain health and safety protocols.
For years we talked about remote jobsite access where we could check a project’s progress by viewing live feeds from cameras and machine sensors. The mining industry has embraced this and my experience in this area will guide my thoughts and recommendations in this offering.
I will go through the COVID-19 workflow and outline some areas that you may want to invest in. These improvements will not be abandoned when the crisis passes but instead become necessary upgrades. When upgrading machines and software there might be components for the machine that need to be purchased. With the machinery improvements, the addition of software is required but not as cost intensive as upgrading machines.
Yes, I am going to mention the need for a good topo which results in a good takeoff. Drone flights can be done safely with results returned to the office. What about a site inspection? You’ll want to get a look at the job and get a feel for it. That is the art of estimating – we leave the good dirt numbers we create using software and look at what it will take to make things happen.
Drone Flight Basics
- Get the crew out and set control points for an aerial topo.
- Fly with a drone to get nadir imagery for conversion to a point cloud.
- Verify the quality of the data in the field.
- Reconfigure the drone to a gimbaled camera forward and down view. This gives an angle to see elevated items visually and not rely on the point cloud.
- Fly two different patterns.
- Run the “lawnmower strips” but lower and with the camera at the described angle.
- Free fly to get specific areas that may need closer scrutiny. Go all around stands of trees, old buildings, and stockpiles as you would do on a site visit.
- Process the drone point cloud as usual.
- Using the ortho image of the job, make notes regarding the detail flights such as where they started and ended. A dotted line of a special flight will help the user get oriented quicker.
- Rename the special flights and correspond the name to the legend on the map.
- Have someone review the files you submit without explanation. After a few jobs you will be able to present a takeoff topo to the estimator that needs no further explanation.
Not to go off into the weeds regarding proposals, but these times have created some special demands. Many of our clients are putting in disclaimers and questions in the bid for further clarification. We have even seen “if/then” line items so the owner knows what to expect if the pre job images could not tell the entire story.
Once the job has been won, it’s time to go to the field. Here are some ideas to consider.
The job trailer may be a thing of the past. Nobody can really go in so all it becomes is storage. Consider a smaller windowless container instead. With site visits being reduced, we need a way to communicate and keep everyone in the loop.
We have had to make a quick shift from in person meetings to all remote interaction. This brings up a host of new challenges.
People need to see what is being done. Set up shareable folders online to give the right people access. Here is how this changes what gets shared.
- Limit the ability of users to post files to your collection. Too many people adding documents can make a mess.
- Use a separate folder for input from those outside your work group. Review the added file and keep it there or put it in the main slipstream for others to review and comment.
- Turn off update notices. Doing this at the start will disable sub-folders as well. When something big has changed, let those that will be affected know.
- Get file structure sorted before the project begins. You can waste hours looking for something in a rat’s nest of file trees and sub-folders. Yes, there will be a lot of files. They are usually updating to base versions. There can be a lot of folders with new and old files available to review. Maintain the dates for these folders but keep the structure and hierarchy.
Now that we are all virtual, there are some things that must change for things to keep moving smoothly.
- Learn how to use your conferencing platform. Know how to mute, operate your video, and change backgrounds.
- Learn how to get your face to look correct. Take a moment to review your video feed and learn what light looks good.
- When using a cell signal for conferencing, things can get slow and you may miss a lot of dialog. Turn off your video to improve audio reception.
- Have ONE person run the meeting. Weekly meetings should have the same person and agenda; yes it will change but keep the structure consistent.
- The worst thing with remote meetings is everybody talking at once. To get over this, we have used raise hands, chat in a speak request or question, and going around the screen for comment or pass.
- Virtual meetings do not have the same impact of in-person. After every meeting, somebody needs to distribute notes as to who said what and what happened so it can be reviewed and commented on.
- Never have a meeting that could have been an email. How do you avoid this? Send out the item(s) as an email first. If there is too much comment or lack of agreement, then it gets to go to a meeting.
Simple change orders are no longer simple. Usually there is a site meeting, and the problem is hashed out. We have helped clients with this issue and there are steps to take that will help reduce the hassle. Start in the field, then move the information to the office.
- Just like with the takeoff, images will be the key to stating your case.
- Drone and ground video with narration done in the office are worth a million words.
- Collect topo data if needed.
- Take a narrated cell phone video to explain the details to the office so the presentation is clear.
- With field data in hand, start to build a story that walks through the problem and proposed changes.
- Always propose an answer.
- Go through the data provided by the field and create the story. Bullet the high points to help with the steps of toe issue and a fix.
- Talk to the field people in an online meeting to verify you have the details right.
- Have the field collect any additional information needed to clarify things.
- Now is the time to make the short, clear story for a person who has not been on the site to feel like they are.
- Images and video with narration as well as the text of the narration included as a Word document are key.
- Send the information back to the field and have them review. If it makes sense to them, you are good to go.
- Do not schedule a meeting! Send the data to the parties involved for them to review and if there are too many questions or issues, then go to a meeting.
- Use their questions and concerns to improve your template for subsequent presentations.
- After a few of these, you will be quick and concise.
Nothing that I have mentioned will die with COVID-19. When we come through this, the ease of performing these ideas that I’ve outlined will continue to live on.
Upgrading machines to generate topo data as well as dirt movement is something worth looking into. I will cover this in a future offering.
Do not be concerned about the software expense and additional training. As you may know, we conduct our business remotely and have been employing these tools for years because we do not live near any of our jobs. From a quick markup of plans on Bluebeam, or a complete presentation with information provided by our client, we make difficult subjects clear.
Start doing this with small items to get your list in order. On larger issues, follow the same playbook and watch how easily and quickly things come together.
Civil surveying is essential for the success of many construction projects, from residential and commercial buildings to infrastructure. It gives project managers and engineers the geographical information they need to build a structure that will stand up reliably in the local terrain and helps them map out how their project should unfold.
Within civil surveying projects, 3D modeling using survey data is a vital technique. The Federal Highway Administration recently analyzed an interchange project in Milwaukee, Wisconsin, and found that the use of 3D modeling reduced operational costs by up to 30.5 percent, especially in the construction of general structures, drainage and bridges.
But what is civil surveying, exactly, and what different forms does it take for different projects? In this guide, we’ll discuss what surveying in civil engineering is, its purpose and how different types of new technology help accomplish civil surveying goals.
What Is Civil Surveying?
Civil surveying is an engineering operation that involves assessing and recording details about an area of land. These observations can then be used to help plan construction projects.
The main purpose of surveying in civil engineering is to determine the three-dimensional relationships between different locations. Knowing information like the distances and angles between points and lines helps engineers determine how to draw up plans for public buildings, homes, roads, bridges and a variety of other construction and infrastructure projects.
The points that engineers measure are often located on the surface of the earth, though they can also be located in space. Because intricate, precise spatial relationships and boundary lines are so integral to this process, civil surveying draws on aspects of different disciplines, from mathematics to geography to law.
Civil surveying also involves specific equipment and GPS data acquired from satellites. High-precision electromechanical and optical equipment is also a necessity for ensuring measurements are accurate.
So, what is the importance of surveying to civil engineers? Civil surveying is useful in a tremendous variety of different applications, including:
- Creating topographical or marine navigational maps.
- Preparing plots.
- Planning for new construction projects.
- Estimating projected paths of roads, railways, power lines and irrigation systems.
- Assessing and recording the boundaries of different properties to determine land ownership.
- Analyzing topography.
- Assessing the position of existing structures like highways, canals, dams and bridges.
- Planning and constructing mines.
- Preparing for military operations and engagements.
- Charting navigational routes.
History of Civil Surveying
The history of civil surveying goes back to ancient times. Egyptians used geometry to reestablish farm boundaries after dramatic flooding along the Nile River, and they used surveying techniques to design and construct the massive, geometrically precise pyramids at Giza, one of the wonders of the ancient world.
During Roman times, the role of civil surveying took on a prominent place in society, becoming an established profession. Land surveyors created the measurement systems they needed to evaluate and create a tax record of the lands they had conquered.
In the eighteenth century, European surveyors developed the technique of triangulation when they realized they could use different angle measurements taken from different places to pinpoint a precise location. And as the British colonized Australia and New Zealand, they used new tools such as measuring wheels, Gunter’s chains, Kater’s compasses and circumferentors, though they also resorted to measuring out paces by foot when necessary.
Gradually, tools like Gunter’s chain — which measures a precise 66 feet, or 1/80th of a mile — gave way to steel bands and invar tapes, and later to electromagnetic distance measurement (EMD) and global positioning satellite (GPS) equipment. Likewise, compasses gave way to theodolites — instruments that measured horizontal and vertical angles with a rotating telescope – which in turn made way for total stations that took measurements of angles and distance with a solo instrument.
Different Types of Civil Surveying
Although construction is the most common type, engineers need to survey a wide range of features, from mountains to oceans to rivers. Engineers use several different types of civil engineering surveys, including:
- Construction surveying: Construction surveying is useful for assessing the arrangement of the buildings, roads, power lines, gas mains and other structures surrounding potential construction sites. Analyzing this information makes it easier to plan construction projects.
- Deformation surveying: Deformation surveying helps to establish if a geographical or man-made feature, such as a road, foundation, coastline or river, is changing shape. In deformation surveying, engineers record the three-dimensional coordinates of specific points. After some time has elapsed, they record the coordinates again to see if they have changed. A comparison of the two data sets can reveal if deformation or movement has occurred.
- Geological surveying: Geological surveying maps out features of the physical landscape, such as rivers, valleys, mountains and more. Satellite data is essential for geological surveying, and engineers frequently use satellite data or aerial photographs to help them in their work.
- Hydrographic surveying: Hydrographic surveying is similar to geological surveying, but it maps out coastlines specifically. Accurate hydrographic surveying is crucial to the work of the Coast Guard and any marine rescue operations. It also helps create navigational maps for sailors and assists conservationists in managing coastal resources.
- Topographic surveying: Topographic surveying analyzes the shape and physical features of a particular landscape. Engineers assess the height of different geographical coordinates and then draw contour lines to indicate areas of the same elevation. They can then use these findings to create topographical maps and to assess terrain for future building or infrastructure projects.
Technology Used in Civil Surveying
Since ancient times, engineers have developed a host of tools to help them survey all types of features. In civil surveying, different types of technology are available, like:
- Computer-assisted drawing (CAD): Once engineers have gathered survey data, computer-assisted drawing helps turn that data into a useful visual representation, such as a map or three-dimensional model. CAD allows for a greater level of precision and detail than could not be achieved with manual sketching or drawing.
- Global positioning satellite data: GPS data is crucial for civil surveying because it allows for the pinpointing of precise locations and coordinates. Where a visual assessment alone would be insufficient for determining whether a corner had shifted or a foundation had sunk, the pinpoint accuracy of GPS data allows engineers to know for sure.
- Aerial photogrammetry: Drones are often useful for the aerial photography necessary in civil engineering. Once they have a number of aerial photographs of the landscape or site in question, engineers can use aerial photogrammetry to extract topographical data from the photos. Aerial photogrammetry combines multiple shots from different angles to create an accurate 3D model.
- Point cloud modeling: To develop accurate 3D survey models, engineers also often create a point cloud or a set of three-dimensional data points. Surveyors use 3D laser-scanning technology to generate a data map of the area they wish to model. Once they have data that represents every surface they need, they can then bring the points together through point cloud modeling into an accurate and detailed 3D model.
Choose the Data-Prep Experts at TOPS for All Your Civil Surveying Needs
When you need 3D modeling to get a construction project or bid off the ground, Take-Off Professionals can help. All our engineers are full-time employees, never contractors, so you’ll always work with someone who is fully integrated into the company, experienced with our techniques and invested and in the success of your operation.
We also stand apart from the competition because we don’t manufacture or sell hardware or software — we specialize only in takeoffs. That specialization has allowed us to develop an unparalleled wealth of technical expertise and vision in civil surveying. We can optimize our work for commercial sites, residential sites, and road work and highway operations, so you’ll always get the customized surveying solution that works best for you.
Check out our compelling list of reasons you should work with us, and then contact us today to learn more.
Surveying is a profession that requires patience and accuracy. Companies across many industries need surveyors to evaluate large plots of land and provide them with detailed mapping and measurements. From construction crews to archaeologists, having an aerial view or 3D model of a worksite is essential to starting and finalizing their work. Without these images or models, workers can’t make informed plans about where to dig, what to fill or where to start building. But surveying in the traditional methods and creating precise mapping takes time.
Drones, otherwise known as unmanned aerial vehicles (UAVs), have been changing the way surveyors work. With their rise in popularity, manufacturers have created drones for a wide variety of purposes, including utility models for companies that need to inspect or collect aerial images of worksites. This guide to land surveying with drones will explain what UAV surveying is, how UAV surveying is being done, what they work well for and how accurate of an image they provide.
What Is Drone Mapping?
Drone mapping is the process of surveying an area of land with a UAV. An operator flies the drone over an area of land, taking hundreds of pictures as it moves. Then, with the help of computer software, they stitch and layer the images, creating a model of the site. This process is also how drone photogrammetry works, and the end result is an accurate 3D representation of the area.
Who Uses Drones for Land Surveying?
Many industries require surveyors to provide maps of areas of land. From establishing the general grade of an area to creating detailed maps of every square foot, drone surveying makes the job easier, faster and safer for surveyors. Among the many industries land mapping with drones, some of the most significant include:
- Construction: There are many answers to how drones are used in construction. Companies need surveyors to start almost any project, but they especially require their help on large-scale builds. Drone imaging aids them in establishing plot boundaries, creating legally acceptable subdivisions and evaluating the suitability of the land before beginning any foundations. With the provided information, construction companies can make important preliminary decisions that ensure optimal safety and legality for the project.
- Oil and gas: The installation of oil and gas pipelines requires a significant amount of planning. Drone surveys help these companies evaluate where pipelines can and can’t go, whether it’s due to proximity to natural resources and conservation sites, preexisting construction or infrastructure or privately owned property.
- Infrastructure: When it comes to designing and constructing new roads and bridges, infrastructure companies need to know the details of the surrounding land. Drone imaging can help them examine areas and determine if they need reshaping or if the land is suitable for construction in the first place.
- Archaeology: Before archaeologists conduct digs, they need to survey the area to decide whether or not it looks like a promising location. Using drones allows them to do so quickly and at minimal expense, saving them time and allowing them to pinpoint interesting areas.
- Mining: Quarries and open mines can be dangerous areas for traditional surveyors, but mining companies often need a mapping of their worksites. UAVs provide an excellent method of capturing aerial images and creating computer models while keeping their surveyors as safe as possible.
Is Drone Surveying Accurate?
Before drones had an impact in the surveying field, creating accurate maps or 3D models of large plots of land would take anywhere from days to weeks. Now, UAVs allow surveyors to create models of comparable precision within a much shorter period. But accuracy in the surveying industry doesn’t have a single definition, and many different models of drones are available.
To understand how well drones perform, you have to consider several factors in regard to accuracy. There are many potential influences as to how well a drone can photograph an area. You also have to consider what you’re using the map or model for and what your standard of accuracy is for the given project.
Survey Accuracy vs. Pixel Size
One of the most essential details to consider is the drone’s operating pixel size. The spatial resolution of the UAV, also called the ground sampling distance (GSD) in technical terms, is the measurement of the space on the ground between two side by side pixel centers in the image. A drone’s GSD depends solely on the specs of its camera, including its resolution and focal length. Different camera models will provide different resolution qualities, resulting in varied GSDs.
When it comes down to measuring precision based on pixel size, your judgment should be based on positional accuracy. Essentially, this means the degree to which the model created by photogrammetry corresponds with the real world it represents. Still, there are two ways of looking at the accuracy of your mapping — relatively and absolutely.
In photogrammetry, relative accuracy refers to the objects within a reconstruction and how they are positioned in association with one another. This applies to any orthophoto map, digital surface model or 3D mapping.
Relative accuracy is an acceptable form of measurement for most cases where the surveyor is dealing with a smaller area or simple uses. It can be helpful for providing general volumes, heights and distances, as well as recording vegetation. However, it’s not the most accurate mapping you can obtain.
Whereas relative accuracy is more general and based on its own proportions, absolute accuracy is based on a geodetic coordinate system. It takes the measurements between objects within the model and compares them to their real-world positioning relative to Earth.
Having a geodetic reference system to apply allows the surveyor or digital model creator to complete more complex functions. For example, they can create professional documentation of surveying, use the recorded geographic coordinates and combine layers for more comprehensive data sets.
Absolute orientation uses ground control points (GCPs), which allow the surveyor to create a coordinate system through the known coordinates of visual landmarks within the image. But to obtain an absolutely accurate mapping of an area with drone imaging, you have to begin by measuring GCPs through professional GPS equipment.
What Influences Accuracy?
Many elements can affect the accuracy of your drone mapping, especially if you’re dealing with the precision of an absolute accuracy model.
First, there are the apparent influences, such as the drone’s ability. Higher quality drones will perform better, from the stabilization mechanics to the camera. Beyond hardware, there are also plenty of outside factors, such as the terrain itself. Particularly rough or uneven terrain can throw off measurements and make it difficult to create a fully accurate mapping. Weather also significantly comes into play, as heavy winds and precipitation can affect the flight speed and stabilization of your drone, especially at high altitudes.
One of the biggest factors that can impact the photogrammetry process is your GCP measurements. However you identify these crucial points, your model can only be as accurate as your starting markers. To create the most exact mapping possible, make sure you measure the GCPs with a smaller unit than the pixel size of your drone imaging. For example, if your drone camera provides an image with 1-centimeter pixels, you should measure the points within a single centimeter of accuracy.
Absolute accuracy essentially builds on relative accuracy, meaning you have to have a proper relative model within the absolute one. Therefore, the accuracy of the absolute model depends on how precisely you measure your foundational relative model. Drone mapping involves taking potentially hundreds of photos with a non-metric camera and stitching them together to create a single image. More often than not, this means not every pixel will be sitting in the perfect position in your relative mapping.
How Accurate Can Drone Surveys Get?
While photogrammetry provides surveyors with a far more accurate means of creating a digital model than other methods, no imaging can be perfectly precise. The ultimate goal is to create a model with the smallest degree of difference possible.
For relative accuracy, it’s expected that maps will have a horizontal and vertical error margin of one to three times the size of the pixels. For absolute accuracy, the margin should be a bit smaller, typically measuring at about one to two ground sample distances (GSDs) horizontally and one to three GSDs vertically. Even if your mapping lies outside these parameters, it may not be an issue, as particularly rough terrain can throw off measurements more than flat or level surfaces.
Drones are exceptionally capable of staying within these margins of error, as long as a trained and experienced surveyor is operating the machine. You can improve your accuracy by way of additional measurements between landmarks, using GPS reference points besides GCPs, improving your drone’s hardware, ensuring you’re working in favorable weather conditions and carefully stitching together the base images.
Where Can I Use Drones for Surveying?
As the use of UAVs has been becoming more prevalent in industrial and recreational applications, the regulations have also increased. Before you can begin using industrial-grade drones to your advantage, you need to obtain legal permission to use them. However, it isn’t a particularly challenging process.
The Federal Aviation Administration (FAA) has control over all methods of aviation, including UAVs. To use drones in a commercial capacity, the official operator needs a Part 107 remote operator’s license. Essentially, it ensures you are knowledgeable about proper use and following regulations. To obtain the FAA license and maintain its validity, you have to:
- Take and pass a test of your aeronautical knowledge at an official FAA testing center.
- If you pass, acquire your small rating Remote Pilot Certification.
- Register your drone with the FAA and renew the registration every three years.
- Retake and pass the aeronautical knowledge test every 24 months to retain your license.
- Follow all FAA regulations, which include but are not limited to drone and control system inspections before operation as well as reporting any accidents that result in injury or significant property damage to the FAA within 10 days of the event.
Once you are a licensed operator, you can use your drones to inspect any areas you are permitted to survey by the landowners. It’s up to you to gain permission to access areas marked private property or land plots owned by companies.
What Can Drones Be Used to Survey?
The benefits of drone surveying cross over many different industries and provide an accurate method of inspecting and evaluating small or large areas of land. These areas may be bare and ready for developments, they may have thick vegetation or they may even already have developed construction. Since there are many purposes for drone surveying, their usefulness applies to many different areas. From flatlands to deep pits, drone imaging provides an excellent way to safely and precisely create models of an area.
When it comes to how drones are used in surveying, there are many answers. Some of the most significant uses include:
Land Development Sites
As technology has improved over the years, land departments have become more inclined to use drones to provide comprehensive land recordings of real estate or property. Drones suitable for land surveying can take orthomosaics, also called orthophotos. Orthomaosaics are groups of multiple aerial phots of an area edited together to form a single image through photogrammetry.
Land departments use orthophotos for things like developing single object mapping layers and updating land cover on preexisting models. They use it even more frequently to create topographic maps for new developments, such as various forms of building construction or designing noise barriers.
Urban Land Management Sites
Drones are exceptionally useful for surveying many different types of land sites, and they make management far easier for the responsible parties. They have nearly a limitless amount of potential applications and services, such as using the digital surface models produced by the drones to create virtual models of plots. They’re particularly useful to urban land management.
Those working within the industry can use drone surveying to import images into computer-aided design (CAD) software to create accurate virtual models of developments. With orthomosaics, which are essentially stitched and overlapping images, management teams can create defined boundaries with the benefit of a precise, aerial view. They can even use the models for more complex functions, such as simulating where water would flow and settle in the event of a major flood and creating a plan to redirect it.
Construction Sites and Earthworks
When it comes to planning for construction, surveyors and the various landscapers and builders are responsible for a lot of preparation. They have to calculate cut and fill projects, complete surveys for pre-construction and as-built properties and oversee the details of the site from preparation forward.
Drone surveying provides these workers with a revolutionary method of imaging and plotting construction sites. It allows them to create an accurate model and plan without continually needing to access the physical job sites, saving time and money.
Mines and Quarries
Surveyors don’t always have the benefit of a safe site. Mines and quarries can pose a safety risk, especially for those attempting to inspect a site at ground level. Geologists and surveyors benefit from using drones as an aerial method of inspection, enabling them to collect accurate data and spatial measurements while lowering the occupational hazards. They also help to boost productivity in quarries and pits, as drone imaging allows workers to make improvements to planning and inventory management.
Beyond companies looking to build and remodel areas of land, there are still many uses for drone surveying. For one, they’re particularly useful in the field of archaeology. With drones, archaeologists can create 3D surface models and high-resolution mapping of potential excavation sites. Doing so allows them to inspect and assess the worthiness of large areas of land much faster and with more accuracy than any other method. It’s efficient, cost-effective and saves their teams a lot of time and energy.
Get Accurate Models From TOPS
Whatever industry you’re a part of, Take-Off Professionals (TOPS) has everything you need to create accurate 3D surface models of your worksite. Our team of professionally trained engineers and surveyors have years of collective experience using drones and accurate photogrammetry techniques to assist our clients. TOPS can help you tackle any challenging project, and with our services, you can start and finish faster and with more confidence.
Partner with TOPS today — contact us for more information or register your company to get started.