The last thing any of us want is a job done wrong due to lack of communication. In a perfect world, the team is on the same page and works out issues at the data stage. Unfortunately, about 20% of our jobs go this way. The industry average is about 5%. My team gets all parties talking at the front of a job due to experience and repeatedly work with firms who understand we are there to make things go as smoothly as possible.
Engineering firms are not to blame. Their reason for not being cooperative may be they are too busy to have a nice long talk about what you found wrong with their job. With proper coordination and your experience as a data engineer, doors will open and there will be better, quicker interaction with designers. Here is how to work things out.
We need a starting point to get things rolling. In our case, it is the building of the model provided after the contractor has won the job. If everything is scheduled correctly, the data is received before field work is ready to start, and there is time for building and review. While building the model, we are looking for a lot of different things.
Overall quality of the plans.
With experience, you can tell when things were thoughtfully prepared or just kicked out the door.
Obvious issues with elevations, COGO, and drainage.
A few spot grades that are not correct is normal. We will fix them and report it to the contractor.
The COGO, (Coordinate Geometry) is another thing. When the layout of a site is not consistent from page to page, we need to let people know. A building must fit, cars need to park, and water needs to be managed. If the site permit calculations call for 165 parking spots and the grading sheet only shows 140, we need to alert the team.
Laws regarding the handling of onsite storm water have changed and become more restrictive. Most sites need to contain and properly drain runoff. Know the rules and verify the cubic footage of water as compared to the plans. If there is a difference, everybody will thank you for not letting the wheels fall off that wagon.
Experience with the engineer and contractor. When working with known entities, communication is easier. We know who to email and where to get results. With new people in the mix, it is best to get acquainted quickly and establish your main contacts.
Share the model with everyone. At the start of the project, try and get the right person with the contractor and engineer in the email loop.
When you have a feel for how good things are and who is committed to making things happen, you are now on course to get things taken care of.
Dealing with Issues
There will be things that need to be changed for the project to work, at least on the screen. Sometimes we see an issue that does not look right, and we bring it to the attention of the contractor and engineer only to find out they wanted it that way. Usually, it needs to be changed. How you present the issue is more than half the battle.
Never bring up a problem without offering a solution. There are two reasons for this:
First, everybody will know you are familiar with the project.
Second, nobody wants to figure things out. We are the professionals in making a surface, we should have some clue for success.
Put together a well thought out email to the group.
This means that when they read the email, they should have no questions.
Do not send out something that says, “call me.” Yes, there are times on complex projects that some type of discussion is important, but for the other 95% of the time, be clear and complete in this communication.
Always put some deadline on the request but don’t go around wanting everything in an hour.
Pick your battles and leave as much time as possible but be sure to put a limit on it. If you do not get results, they should know you will go ahead and change things or just leave that section out of the model. That will get you answers.
Don’t sweat the small stuff.
A fat-fingered elevation is no cause for a Zoom call. Just make sure you note the changes made in a communication to the core group.
Everybody is busy. The engineers’ process for dealing with the problem you present may take a meeting on their part.
The message here is to note issues early on so the rest of the project can move along while the details are worked out.
When working on a project, we want everybody to get a copy of our data. It is always better to have several eyes on your work so there are no surprises down the road. In over 80% percent of our jobs, we will provide working files to the surveyors to help them with their portion of the job. This covers several factors:
The surveyor can look at the data and let us know if they feel changes are in order.
We are already producing a lot of the information needed for layout, so we can add points or a subgrade file for the survey crews to get to work.
The survey bill to the contractor will be reduced. No surveyor wants to be stuck in the office doing calculations to send to the field.
It has taken a lot of years to get to the point where we have the trust of most of the large engineering and surveying firms in the country. Now that they are familiar with our work and competence, we are welcomed into a job. If this is your first time with a group, proceed slowly and earn their trust to prove your capable of providing accurate information.
Take Off Professionals is always open to sharing our experience and knowledge. Contact us online for assistance with dirt takeoffs, 3D models and more, or call us today at (623) 323-8441.
Topographic surveys allow you to map the terrain of a given landscape that you’ll be working on. These surveys incorporate everything from trees to existing buildings and utility poles. They can also map the various elevations on your job site. You can use topographic surveys to gain a better understanding of the landscape of your next project.
What Is a Topographic Map?
Topographic maps are visual models of all of the data collected during a survey. Your map will show all the elevations, natural and human-made constructions on your job site. Contour lines will denote the various elevation levels on your property, and there will be markers for everything else.
How Do You Use Topographic Surveys?
Topographic surveys help you determine the geography of the terrain. When you build new structures, you need to have an understanding of your landscape. You can use a topographic survey to determine the best locations for your new buildings or utilities. It will also tell if you need to perform any additional work like leveling.
Topographic surveys can also help you determine whether any areas on your property are off-limits due to elevational or other challenges. You can use a topographic survey to gather ideas about how the landscape will look once the construction is complete. Topographic surveys allow you to follow the necessary steps to reach the desired outcome.
What Instruments Are Used to Take Topographic Surveys?
Modern technology offers a few simple ways to create a topographic map, including:
Global positioning systems (GPS).
Electronic distance metering (EDM).
Trained professionals use these devices to take measurements and compare them to existing maps. The surveyor can then develop a topographic map demonstrating every detail about the terrain.
What Industries Use Topographic Maps?
Topographic maps are useful in several different industries. Some of the most common jobs that require topographical surveys include:
Architecture and construction.
Topographical surveys and maps are often used as the basis for a 3D blueprint for individuals in these sectors. A visual representation of the land features allows the workers to get a distinct sense of what they’re working with and how it might turn out.
Contact Take-off Professionals About Our 3D Model Services Today
At Take-off Professionals, we take the data collected from surveys and develop 3D topographical maps. Our team of full-time professionals is ready to help you visualize the data for your next project. Our primary focus is on optimizing data so you can use it effectively.
You can use our platform to access your data and upload additional files and notes. We’ve been working in this industry for over 20 years, making us experts in our field. Our teams work on around 1000 3D models each year.
We can offer you a detailed quote and fast turnaround times. We’re available on a national scale with technicians stationed in offices in three time zones.
Construction surveying is an integral part of the build process. Ensure that you’re completing the steps correctly to make your property safe and functional.
What Is Construction Surveying?
Construction surveying is staking out or determining reference points for the construction process. Construction surveying is about seeing what is already on the location. These items could be anything from patches of trees to existing buildings.
Construction surveying is also used to determine where the location of any new buildings should go. Keeping all of this information organized is vital to the construction process.
Why Is Construction Surveying Necessary?
When you start on new construction, you want to ensure that your plans will come out the way you intended. You need to know how to execute them to match your vision, keep your workers safe and follow any laws and guidelines. Construction surveys help you determine the safety of the land where you want to place a building, roadway or bridge.
Construction surveying allows you to better understand the area you have to work with. Ensuring the location is viable for the new build is vital to keeping workers, partners and clients safe during future use.
What Should Be Included in a Construction Survey?
You should include several elements in the construction survey process, including:
A basic border survey that marks where your property ends and another begins.
Some information on easements, other building locations, underground structures or utilities.
An outline of the elevations and contours of the land.
A plan of where new facilities and roads will go.
A reexamination of the finished project to see how closely it aligns with the measurements.
What Equipment Do Construction Surveyors Use?
Gathering all the information listed above requires specialized equipment. Some of the machines and tools construction surveyors use include:
Levels and theodolites: Surveyors use these instruments to measure angles, horizontal and vertical slopes.
Electronic distance measurement: Surveyors may also choose to use these computerized tools to take measurements.
Global positioning systems (GPS): Surveyors use GPS devices to measure and collect information about the land.
Geographic information systems (GIS): Surveyors can use these devices to create visual maps that represent all of the data they collect.
Contact Take-off Professionals About Construction Surveying Today
At Take-off Professionals, we understand the importance of accurate construction surveying on your next project. We are a team of full-time professionals who build 3D models for your construction jobs. Our only focus is to take your data and create something visual from it.
We have a platform that you can use to access your data and add other files and notes. Take-off Professionals has been in business for over 20 years, and we work on a national scale. We work on around 1000 3D models for machine controls every year. Our team provides detailed quotes and fast turnaround times, so you know exactly what you’re getting when you partner with us.
Incorporating GPS machine control into your earthmoving projects will help you in various ways. You can ensure you complete the work to the best of your ability by using machine control with 3D terrain models. Combine our services with your machines to make your business stand out for competency and dependability.
What Is GPS Machine Control?
GPS machine control involves the use of several instruments to give feedback to operators on grades and equipment positions. Some of the most common positioning sensors used to gather this information are:
Advanced GPS systems.
Creating a 3D model from predetermined positions gathered through GPS machine control increases accuracy. You can use equipment like dozers and excavators with the collected data to complete an action at exact coordinates.
Machine control technology works with the help of GPS and the Global Navigation Satellite System (GNSS). Earthmoving machines receive signals from these systems and compare them to the model of the proposed plans. This process allows the equipment to determine exactly where and how to grade the terrain.
You need a base station to ensure accuracy, however. Satellites are typically off in their measurements, making them unhelpful for precise work like earthmoving. The base station corrects these errors, allowing for a more accurate reading. A base station sends the reliable reading to a rover, developing a 3D map of the area and determining its location.
Who Uses GPS Machine Control?
Workers in any industry that deals with earthmoving equipment can benefit from GPS machine control. This technique is common in the following projects:
With GPS machine control, your team is more likely to do the job right the first time. Satellites that feed data to a machine take out all the standard work and make earthmoving jobs much easier than ever before.
Contact Take-off Professionals Today for 3D Modeling Services
Ensure your machines are working with an accurate 3D terrain model with the help of Take-off Professionals. Our team can optimize your data and make a map that works well for GPS machine control. You can access our platform to view the data and models and add any other files or notes.
At Take-off Professionals, we focus on creating reliable 3D data models that you can use for earthmoving work. With over 20 years of experience, we how to get the job done. Our team develops around 1000 3D models every year.
We’re proud to offer detailed quotes and quick turnaround times. Our staff is available nationally with employees stationed in multiple time zones. Reap the benefits of using GPS machine control for your earthmoving projects. For more information about our 3D modeling services, please contact us online or call 623-323-8441 today.
When civil engineers first plan to develop a property, they require land surveyors to provide accurate measurements and information about the land. As a result, land surveyors are critical to civil engineers who want to do their job properly. By working closely with land surveyors, civil engineers can increase their project’s safety, improve efficiency and ensure they comply with various standards.
Find out more about what land surveyors do and how these professionals assist civil engineering projects.
What Is a Land Surveyor?
Whenever an individual or company purchases a property to develop it, land surveyors play an essential role. Land surveyors are responsible for mapping and measuring a property’s land to establish property boundaries. They also provide information about the property’s topography and existing buildings or improvements. Surveyors can give clients precise measurements and data about a property, and they’re regularly employed for construction, engineering and mapmaking projects.
Given land surveyors’ expertise in determining topographic heights, land sizes and land measurements, they regularly advise the work of other professionals. For example, they often guide the work of geologists, developers, town planners, architects and engineers. You can even see them in governmental roles, helping sewer, power and water authorities receive the information they need to do their jobs well.
You’ll typically find land surveyors conducting measurements at the beginning of a development or construction project. They make their measurements, map the land and give this information to architects, who use it to design their projects with the landscape in mind. Land surveyors also provide their measurements to engineers, who use the data to ensure any planned structures are safe.
Boost Your Civil Engineering Project with Precision
Build on the strength of accurate data from land surveyors with TOPS. Our experienced team, driven by precision and dedication, creates 3D data to enhance site work, machine control, and layout, setting your earthworks project up for success.
How Do Land Surveying and Civil Engineering Work Together?
While public works, such as public education facilities or health care institutions, are some of the most common civil engineering projects, you can also find civil engineers helping organizations build bridges, pipelines and canals. Since civil engineering often requires structures and other infrastructure to be placed on top of the environment, land surveyors play an important role.
Infrastructure needs to be safe and fit the land it’s built on, so civil engineers need accurate land surveys before they begin their work. A land surveyor provides engineers the data they need to ensure their project doesn’t negatively affect protected environments. They also give engineers the measurements and information they require to ensure any structure they build will be safe. Land surveyors can even help engineers ensure their project has peak efficiency.
To support a civil engineering project, a surveyor will look for several land qualities. For example, they’ll often note the nature of the land, such as if it’s grassy, rocky, clear, forested, flat or uneven. They’ll also collect data about the angles and distance between critical points and measure relative elevations.
Information on natural features, such as rivers and hills, are other types of data included in land surveys for civil engineers. A land surveyor will also include data on human construction, such as power lines and roads. If a civil engineering project requires a map, land surveyors can produce it.
Once a project ends, civil engineers require an as-built survey from a land surveyor. This survey is meant to determine how accurate the initial survey’s data was after the project’s completion. The land surveyor will create a new survey designed to check that the earlier measurements match various details and positions of the final project. Civil engineers require surveyors to repeatedly survey a structure to ensure it’s safe and has the appropriate technical performance.
Why Is Land Surveying Important to Civil Engineering Projects?
One of the biggest reasons civil engineering projects need land surveyors is that they provide accurate data engineers can use in their proposals. Land surveyors are also important because they can conduct inspections in high-risk areas and help resolve legal disputes. Learn more about the importance of land surveyors and some of the essential ways they aid civil engineering projects:
1. Provide Accurate Data for a Proposal
As civil engineering organizations create proposals, they need accurate data. When a civil engineering organization submits its proposal, it often needs to gain public support — whether through lawmakers voting on the project or the public directly voting for it. If a project appears dangerous, it can sink, leading the public or lawmakers to vote against it.
Accurate data helps engineers create a proposal that shows the infrastructure will be as safe as possible. For example, a land surveyor might use a 3D simulation via drone survey to show how a structure will impact the environment. If the survey reveals a new road could lead to erosion in the surrounding area or impact water flow, civil engineers can adjust their proposal to account for these potential dangers.
With accurate data in their corner, engineers can prepare more detailed proposals. These detailed proposals help lawmakers who want the project to pass, as they can more easily showcase how safe the project will be in the future and how it will change the current environment. Since safety is a huge public concern, civil engineering firms may find it difficult to get public lawmakers on board with a project until they prove it doesn’t come with high risk.
2. Conduct Inspections for High-Risk Areas and Projects
When civil engineers need to work on high-risk projects, such as bridges, they often turn to land surveyors. Surveyors usually have the equipment required to safely assess a project site without putting staff in danger. For example, a land surveyor can use a drone to assess high-risk areas that people can’t easily or safely access. Using a drone is much safer and can deliver more detailed results, as it can navigate around complex terrain or structures and gain a bird’s-eye view of a property.
Since civil engineers play a major role in creating or repairing high-risk projects, such as dams, canals and bridges, they need highly accurate data to ensure they don’t put the public in danger. If a dam breaks or a bridge crumbles, it can lead to injury and death. A land surveyor can conduct a survey before and after a project to ensure civil engineers have the necessary data to build safe structures.
3. Help Resolve Legal Disputes Between Public and Private Property
Sometimes, civil engineering projects face disputes over private and public property. A private landowner may believe the project crosses over to their property, while the civil engineering firm may believe their project only goes over public land. When there’s a dispute about property lines, land surveyors can help to resolve it. Usually, a land surveyor will conduct a boundary survey to establish whose land the civil engineering company is developing their project on.
A land surveyor will often use a drone to conduct these boundary surveys, as they can establish property lines faster. With a bird’s-eye view of the property lines and the use of other surveying technology, they can quickly find where private land stops and public land starts. A land surveyor may also use LiDAR scanning and UAV technology to ensure their surveys are as accurate as possible.
By using advanced technology to complete their boundary survey, a land surveyor can quickly resolve legal problems and stop delays from occurring. These surveys can also increase public support in the project, as people will know the civil engineering project is only using public land.
When Do You Need a Land Surveyor?
When you plan to develop a piece of land, you’ll need a land surveyor. Since you’ll need to comply with your project’s end goal, building goals and local regulations, a land survey is an essential part of development. With a land survey, you’ll gain a better understanding of the site’s topography and dimensions, giving you critical data to ensure your project doesn’t run into compliance issues.
One of the most important times to use a land surveyor is when you’re planning to change the land’s use. In this case, you might need a planning permit. Part of attaining this permit involves receiving approval from a local government, where they’ll check overlays, land zoning, municipal strategic statements and permitted land uses. A land survey is often required to ensure your project meets the aforementioned permit requirements.
Land surveys are also necessary when a project has different zoning requirements on a site. For example, a piece of land may have various overlays on it, such as protections for vegetation, wildlife or heritage. You might find that land has different local provisions, such as plot ratios and building heights. With these various zoning and land requirements, land surveys are essential. These surveys give you data about topographic heights and land that is critical for addressing zoning requirements.
Another time you’ll need a land surveyor is when you’re working on a sloped site. Since a land surveyor can use specialized equipment to measure horizontal distance, they can assist civil engineers who might not have equipment capable of making these measurements. You can also rely on surveyors to measure vertical distance. These measurements are critical when your project requires you to excavate a pipeline or build a drain or road.
Essentially, any time you need to know exactly how a project will fit on a piece of land, a land survey is needed. Whether you’re constructing a new bridge or upgrading a road, land surveys allow you to know how your planned structures will fit with the land and ensure your project won’t cause safety issues.
Benefits of Land Surveying
Many civil engineering firms and organizations rely on the benefits of land surveyors to improve their projects with the following:
Increased boundary accuracy: One of the many land surveying benefits is helping civil engineers establish accurate boundaries for a piece of land. With the right property boundaries established, a civil engineering team can better plan out construction and development. Accurate boundaries also help teams avoid legal disputes with people who own land near their project, saving time and raising public satisfaction with a project.
Greater understanding of topography: Before civil engineers begin a project on a piece of property, they need to know its topographical details. A land survey ensures engineers have a better understanding of topography, such as determining if the land has any structural or soil issues or if it is prone to flooding. By gaining a greater understanding of a plot’s topography, the civil engineering team can determine if their project is feasible and safe before they begin development.
Better property division: When a civil engineering firm makes their proposals to local authorities, they need to ensure they’re not building on private property. A land survey gives them better property division by clearly showing where public property starts and ends.
Improved construction preparation: Before a civil engineer OKs construction, a land survey can give them various data about the plot. This land survey’s data can help civil engineers ensure any structures are placed in the ideal location and that any necessary preparation has been completed prior to construction. With this data, a civil engineer can provide their construction team more accurate plans and help them better prepare for construction.
More accurate value estimation: Land surveyors can also help civil engineers and other professionals determine how much a piece of property is worth. By having a detailed land survey, you can more accurately value a property based on its landscape, hardscape and location details.
Choose Take-off Professionals for Your 3D Data Needs
At Take-off Professionals, we understand the need for accurate data from land surveyors for the success of any civil engineering project. After receiving data from surveyors, our experienced engineering team creates 3D data to assist with site work, machine control and layout. Alongside our engineers, we also employ surveyors and 3D techs to ensure any models we provide are extremely accurate and give you the information you require to ensure a project is safe and can be completed as efficiently as possible.
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:
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 modeling 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.