Paving Rehab Data

Paving Rehab Data

The U.S. Interstate Highway system is almost complete. Regional networks are mature, and the new right of way is geared for housing. Luckily, we still see new alignments and the percentage is increasing for repaving and full reconstruction. This increase has led us to become efficient with sometimes difficult road improvement jobs. Let me explain.

Types of Rehab

There are three basic types of road rehabilitation all requiring a different approach to the data. While I have defined the types for data purposes, there are projects that can be a combination requiring a change in the process.

Full Rehab

This is the easiest and currently the most popular type we perform. The road may move horizontally and/or vertically and none of the previous roadway elements are to remain. Paving, curbs, and driveways are all replaced. Ditches will usually be reworked, if there is an underground storm system, it may change as well.

With everything being new, it may not make sense to refer to this as rehab. The reason is at some point the work you are doing will need to connect to something that will not be moving. Driveways, buildings and off-right-of-way drainage are required to match-in with the least amount of disturbance possible.

Mill and Fill

Asphalt paving does not have a great life in many parts of the country. Freeze-thaw in the North, water and heat in the South, and brutal sun in the West define the finite life and eventual repair of the wear surface. When spot repair is no longer possible, the road surface will be milled, and a new full-depth mat will be laid on the freshly compacted base.

We will go into detail later, but the curbs are usually in good enough shape to keep. We are now required to respect the vertical and horizontal constraints of the existing road. In addition, there are required minimum and maximum coverage and lifts for the base and wear surface. This gets difficult to work with, as there are many constraints plus having little or no ability to try and fit everything in.


Right of way acquisition is usually done with the future in mind, especially with larger arterial roads. As traffic counts increase, lanes are added to accept the load. When confronted with a widening job, we are concerned with two major points. First, the condition of the edge we are joining to, and then the topography of the extension. I will detail these in a moment.

The Basics

When doing rehab work, we usually go the route of a road job. Alignments and templates are a good start to get things right and, most importantly, a way to easily adjust as things change. The single biggest issue with rehab projects is the dynamic nature of all the parts that need to come together. Here is an outline of what we like to see.

Horizontal Alignments

Ordinary COGO (Coordinate Geometry) will be provided when doing a new road. Sometimes in a rehab job, the plans call out for following the existing road center. Yes, this is a loaded statement from the designers. There may be a line on the plans that might be an old alignment, or something drawn for convenience. Alignments with good instructions are easy to get on your screen, but what about that mystery scratch in the near middle of the road? There are several alternatives.

If you can’t get a good centerline from the CAD, you need to decide on how to guide machines for the work. A best fit centerline takes the edges of pavement and averages the distance between them to give you something to steer to. Here is a set of shots that were taken along the existing edge of pavement along the slip formed curb/gutter.

There are many ways to get an alignment, in this case I am using Carlson’s Best-Fit Centerline. You can use points or lines. Here I drew lines through the points with arcs in order to give the program a smoother start to figuring out a centerline. The alignment is drawn through the upper line (shown above) and will offset to get it to the approximate center.

I often times will do this on the other side of the road as well. When this is necessary, you need to either make a new averaged centerline or create two different roads using one for each side. These cases are generally for older, small streets and roads where environmental conditions have caused heaving and erosion to move the curb. Logic says we will replace those sections so this is a rare exception, not the rule. Knowing that, you are now able to fix real issues.

The new centerline is shown here. It deviates from the edge by almost 3-feet in the worst spot. This is too much. Changing the parameters will tighten things up. This is shown in the video.

With a good alignment to steer to, we will now work on the vertical.

Vertical Alignments

With horizontal alignments we are trying to get a centerline close to actual. With a vertical alignment, the stakes are higher. When the vertical profile corresponds with the centerline, it must follow road speed rules regarding cross-slope and the finished job needs to look good.

The job depicted above has 3D shots along the edge of pavement, as well as, centerline shots that are turned off. With these 3-points acting as cross-sections, we can create a good existing road surface as cross-sections. Don’t be alarmed if a contoured surface looks bad, a cross-section look is the best way to generate a finished product.

I have used Carlson’s Road Rehabilitation Profile command with good results. You will need to get things in order, including some of the outlined steps I will reference. When the pieces are in place, you will have access to the options shown in the dialog box. Lots of power is provided to automate a sometimes-difficult task.

With the alignments done be assured you will be revisiting these to make things work better. We will generate cross-sections to verify the quality of the data.

The following is the Carlson section alignment dialog box. There are enough options to give you the results you are looking for. I am using these options for the job in this article.

With the section interval and special stations defined, I will now create sections of the existing road to give me an idea of what I’m looking at.

Gathering Existing Data

I need to mention a critical point. When we work with clients who build models, we insist the shots are taken with a total station. GPS accuracy is not reliable for the number of required shots and would take too long to get low residuals. A robot and one person can shoot quickly and with accuracy to make sure we are not wasting time. We accept GPS shots only to fully rebuild the job after receiving good data.

Section Review

The production of cross-sections will be the true test of what needs to be done next. I have spent a lot of hours getting things ready for production on rehab jobs. The constraints of the existing features that remain and the rules imposed by the parameters of the road design make the task difficult. It may be necessary to rebuild the job several times in order to make everything work.

Also be aware of the hierarchy of importance in case something must give. For example, we need to keep the curb but need to go less than the required 2% slope. That’s an easy one, but there may be situations where several rules need to be flexed for things to work.

Here is one such example. The road is straight and calls for a 1.5% cross-slope. The right side of the road is almost flat. We need to review up and down station to see how far this extends. The solution here was a 75-foot curb replacement due to heaving of the existing curb and gutter.

With requirements that are often out of the requested values, this type of work takes more time. Many rehab jobs just want to follow the existing road, mill the existing surface and come back with minimum cover. This type of job still needs data to work correctly.

Carlson has a tool I have used with great success. The Match Reference Section Slope command allows you to specify the desired slopes and the limits of deviation to it. Here we are trying to get a 2% cross-slope with a variance to try and make things fit better.

After filling out the dialog box, the command has listed the varying cross-slopes generated by the settings.

Adjusting the Parameters

There are two tools I use to verify a rehab design. The first is the actual material to be used. At some point there was a takeoff done, and I want to make sure we are in the ballpark.

This is just a portion of the report, but the totals are in line. To adjust things, go back to the Process Options dialogue box and check the Adjust Template Grade Table. The side not associated with the Profile Grade will adjust. This may push the slopes outside the design parameters and require a variance to get the volumes down.

I will then plot the sections to verify the profile is doing what I want it to. With a small road like this there is not a lot of room to move, but if the job is several miles long small tweaks can bring big savings.  This particular road is getting 8-inches of white paving. The red is the sub-base needed to bring this up to grade. Had this trend continued for several stations in both directions, I would revisit the vertical profile to try and pick up some material savings.


The task may sound daunting, but the job needs to be broken down into the individual parts that make up the job. I have tried what seemed to be quicker and easier methods, but changes are near impossible and always take longer.

Approach each part of the process as a separate task and the delineation makes things easier to imagine. With more of these jobs coming along every day, it pays to be proficient.

I have featured Carlson because I have experience using the commands for road rehab projects. Other software can accomplish the same tasks. The commands will be different, but the procedure remains the same.

Curb Alignments for Machine Guidance

Curb Alignments for Machine Guidance

More contractors are taking advantage of stringless curb technology today. At TOPS, we got involved with stringless curb when it was proposed as an alternate application for machine control. In their quest for increased productivity, some of our clients are early adopters which we credit with our first-hand experience in using the technology.

The Concept

The idea is straightforward. Adapt the use of alignments for paving systems to a curb machine and eliminate the string. There isn’t more to do for the transfer of the guidance and the technique seems easy to perform. Unfortunately, we encountered some problems along the way. But lucky for you, we have taken the time to point them out and guide you on this process.

Stumbling Blocks

You need to build an alignment-based project that has the usual elements, horizontal and vertical alignments, and a template. Brands vary but the template can be used to pick the side of the alignment the curb is on, as well as, slope for fill or spill curb.

One of the difficult things to do is to make the alignments as if you’re in the field doing the work. This varies for our clients and it is something you need to coordinate with the curb crew.

In the example here, I bring up two interesting points:

  1. This job is the addition of more parking to an existing lot. When joining to that curb, we need to get accurate shots in order to smoothly pick up the slope of the current to future curb.
  2. The 90-degree corner will necessitate a stop in the alignment. The question for the field is where to start one alignment and stop another.


As with any road job, a horizontal and vertical alignment are required. With curb, things need to be different. There will be some figuring with both.


Each curb is a separate road job. As shown earlier, you need to coordinate with the field as to the start and stop points. Experience has led us to have this consistent, but it takes time to coordinate. When you get it figured out, it will stay standard for the most part.

When working with a closed island with all curves, the line needs to either stop short of the end or go past it and not be on the same path. This example shows the alignment stopping .10 feet from the start. This gives the machine a chance to complete the run without the software problems of an alignment running back on itself.

We will also have the alignment bypass the start by a couple hundredths of a foot when it gets back to the start point to keep the lines from intersecting.

While building the alignments you are also providing a full takeoff of the curb so the field can schedule concrete and plan the pour accurately.


This is where things get interesting. We all know that good plans have elevation callouts for the major points of a curb. This example is trying to do that, but this job has sheet graded contours that make things more difficult. We need to pay attention to closed areas that may trap water and make them back-flow into the main slope plane.

Breakover Angles

This is by far the most critical part of designing stringless curb files.

Here are the elevation points as called out in the plans. The curb moves along but there are angle breaks with a 2% delta. When entered into the machine like this they will cause it to abruptly change slope and make a mess. To remedy this, two things must happen.

  1. Vertical curves must be added to the alignment to smooth out the transition in slopes. Our method for figuring the amount of curvature has been derived through experience working with machine control and curb machine vendors. Experience will need to be your teacher here.
  2. After making the curb look right, the new edge of pavement 3D information needs to be incorporated into the model so the subgrade and paving are not affected.

Here is the alignment after the addition of the vertical curves. The transition is now smooth, and the machine will make the slope change gradually so things look right and perform well.

In the images, the difference may seem subtle. In the field, it is scary to see the machine try to do an instant 3- or 4-degree slope change. I’m sure the question will come up in a cart and horse fashion. If you are changing the parking lot surface, should you design the curb first? Most jobs don’t use stringless curb. The ones that do are usually requested after the surface file has been made and the curb contractor wants to use the technology.

The initial file creation is procedural and a process should be followed. This is because there may be 50 alignments for a big site job, and you don’t want to go back and check every line to see if you missed something. There isn’t much rework involved after the curb alignments are returned to the surface, we just want to make sure base depths conform to plan. The following is an outline of the entire process.

Create Curb Template Alignments

  • Save the file as a new version to keep the surface file alone
  • Create breaks for machine control
  • Create a vertical and horizontal alignment from the curb lines
  • Station the horizontal
  • Add vertical curves to smooth out the profiles
  • Create the proper exportable road file. Brands and requirements vary

Create New Surface

  • Do another save with a new name
  • Remove the use of the initial curb elevations in the model
  • Set the vertical profiles as the new curb lines
  • Offset the lines in three-dimensions to get the lines locations and elevations to gutter or edge of pavement
  • Adjust the surface in areas that make it smooth and well drained

A bit easier said than done, but experience has really helped us get this operation efficient. The curb files we make for clients can guide stringless curb with confidence. I remember years ago when the head of Gomaco asked me why I thought anyone would use stringless and how I planned on giving the crews confidence to spend tons of money and time with no string to lead the way. Here is what I stated and how a company gains trust.

  • The curb (or white paving) is derived from the model used to blade the surface. If that looks good, things are okay.
  • Use a 4-wheeler to do a dry run. Load the road job and drive along the curb, you will see any problems before the pour.

With all these advantages to stringless mentioned, file preparation is not a big chore. I have some sad stories about stringline that caused us problems over the years. A few dry runs of practice and maybe some “air-paving” will get you comfortable and ready to make the move to automating curbing and paving.


Using XML in Civil Construction

Using XML in Civil Construction

Extensible Markup Language (XML) is used throughout various coding and language platforms. In our field it’s used to produce and transfer data types for data prep and site construction. There are two versions of XML (1.0 and 1.1), and both will import into the current software used by civil professionals.


The basic format for XML was a good starting point for different industries. Autodesk started the widespread use of XML and import/export ability was added to more software as the code matured. Most development by commercial software vendors began to drop off after version 1.0 released in 2002. Version 1.1 is capable of additional and enhanced data but never got the desired traction.

Enter Carlson

Carlson Software of Maysville, Kentucky picked up the LandXML development process and produced version 2.0. The addition of textures and advanced data types was a good idea, but support from other platforms is lagging. I don’t think much more will happen as 2.0 was in draft as of 2014.

This image is an import of a LandXML file imported into Carlson’s Precision 3D. It includes textures, polylines and field-to-finish data such as the light poles seen along the road.

If this file were imported into another CAD program not supporting 2.0, the data would be limited to surface elements. In other words, a TIN surface with faces and breaklines would be generated without any additional data.

Understanding XML

XML documents, in a basic discussion, are made up of markup and content. We also need to look at the header section of an XML document, as it contains information we may need.

The XML Header

Importing a file into your software is usually not a big issue. Bringing in CAD and point files is routine. An XML import should be no different. Where there could be an issue is with the XML units and how they are interpreted by the software. Let’s look at an XML header.

  • We know the time and date the file was last saved
  • This is a version 2.0 file. Software that only reads 1.2 will still import information, just not all.
  • Know which units were used in the file. Know your software, some will not alert you of a unit mismatch. An example is provided in the corresponding video.
  • We have our first look at a tag with the unit(s) callout.

Markup and Content

Markup begins with < and ends with >. Between those constraints lies the content. It also encloses tags which can have content following. Anything that is not markup is content. That rule is not absolute but for civil XML files this will be what we see for the most part.

If we drill down in this section we see a surface named All Roads and Drives.  A Boundary will be created using the PntList3D points. Note the points are not comma delimited. They are Northing, Easting, and Elevation in a continous string seperated by a space.

In the next example, the screen shot calls out several boundaries and the connected points to make them. The boundaries are individual markup callouts because each 3D line encloses a different street. This will start and stop line generation for each street.

Here is a 3D view of drawn smaller boundaries. This also allows the closed line to be used in texture rendering and vertical adjustments.

In this file the surfaces that make up the roads are shown after the boundaries are written. The markup and content give you the type and ID of the TIN edge verticies as points. When the points are brought into the file, the TIN edges need to be called out so they form correctly. Shown are the end of the TIN points and the beginning of the point numbers that form the faces of the TIN.

The production of the TIN faces, (edges) continues to the end of the file.

Here are some things you will want to find out before importing an XML file. Be sure to make a copy of your file so edits can be undone if need be.

  • Most critical to review are the units. U.S. and International feet can cause problems. Note that International feet will be called “foot.”
  • Determine the software that produced the XML. This can come in handy. It doesn’t happen often, but files produced by different platforms don’t always import properly.
  • The XML file may contain coordinate system information letting you know how the job was set up.

  • Sometimes you may not want all the information provided in the file. You can clip out the tags and related elements you don’t want to import. I agree that all you need to do is delete the unwanted element. However, that unwanted element could be a huge surface or something that stops the file import and shuts down before the elements you want get put on the screen.
  • The original project name is often times included as a tag. This can help you verify dates and times to confirm you are working with the latest and greatest.

Why Use XML

The ease of producing, sharing, and importing XML files has made them the format of choice for data transfer. Large scan and photogrammetry surfaces can be easily digested by smaller office computers as opposed to point cloud formats.

With this ease, many people are transferring data in this format. I have outlined some steps for users to make file sharing easier. The knowledge gained by reviewing the raw XML in a viewer cannot be over emphasized. Take some time to look at files that have worked for you in addition to those that gave you issues.

When you get to know what’s in a file by reviewing it, your confidence will increase as well as the ability to verify sources and validity of files. Work with some files and contact me with any questions or issues you have.

All About TIN Surfaces

All About TIN Surfaces

The building block of a surface used in civil and architectural 3D modeling is the TIN (Triangulated Irregular Network). We will go over its definition, rules, and tips for making this format perform. Let’s get started.

The TIN surface


A TIN (triangulated irregular network) is the format used to transmit spatial ideas into something that can be transferred to the ground for civil (and architectural) work. A TIN consists of triangle definitions that have x, y and z coordinated for each of the three points. The triangles do not overlap and share common intersection points.

The triangles can be any configuration and size. The only limitation are the three sides. The triangles are all flat planes (NOTE: this will be important to remember later). When generating a TIN, you will often see some large triangles, some with long edges and some with very small edges.

The vertices of the triangles are generated from 3D elements provided from the following three elements you will create. They are 2D lines (contours), 3D lines and points. The vertices are made up of how far apart they are interpolated and elevations assigned to these elements.

TIN Faces

The connected 3D points that make up the TIN are TIN edges. They should not be looked at as lines but instead as a visual representation of the edge of the flat triangle. This will tell you where the grade breaks to the next triangle are so the surface will perform the way you want.

TIN Breakover

The TIN Breakover refers to the angle from one flat triangle to the adjacent one. This is important to mention because if the angle is too great, you can add more points therefore generating more triangles and softening the severity of the angle.

In this example, the slope between these two triangles goes from .48% to 3.47%. Smaller triangles have been added to smooth their transitions.

You may not always want smooth transitions. Starting with the top or toe of a slope, you will want to hold a 3:1 ratio as it flows to a flat bottom. In this case, be sure to add enough data points so there are no errant elevations in that area. This will be covered more later.


TIN Density

If 10 is good, 100 is better, or so we used to believe about surface triangles. The short answer to TIN density is to add just enough to make the surface do what you need it to. Currently, the advantage is that faster computers and segmented TIN handling have made things better. Field firmware can break up surfaces to load just the area you are working on and not the entire file.

Over the years I have come up with guidelines to help users get closer to the balance of surface, size, and performance:

  • Try and make all the triangles (in an area) the same size. This insures smooth edge transitions and helps large grader blades operate better. In this screenshot there are similar sized triangles in a parking area. You will need to add more triangles as things warp and not just slope like this example. Be sure to add where needed.


  • For this example, triangles need to be added because of the arcs on the parking islands and the changing slopes. These elements require that water is pushed away from the parking curb into the drive area. Never assume that the number or appearance of triangles indicates the quality of a surface. It’s just a starting point. We are looking for a surface that does what is needed for that job, which changes all the time.
  • Do not confuse TIN density with the actual point elevations you assign. Add points where the grade must change. Look at a surface like you are laying out points to grade to. A blade will connect those dots. That is where TIN density comes in.

Density Settings

Software can densify surface points when it makes the TIN. There is no need to add these points during the line/point process as they are densified in the settings when it is time to make the TIN. When working on a surface, we will not add additional points, so we can see the work we are doing. When we like the points/lines we have made, then we will increase point density. This increase in points will address the issues I have been discussing like breakovers and detail areas.

Business Center addresses this in the settings as the maximum sampling distance. I will also address the tolerance items in a bit.

Carlson allows the distance to be turned on and off while keeping the setting.

The horizontal and vertical tolerance settings refer to the middle ordinate of the cord that represents the arc. That distance is the maximum a chord line can be from an arc.

The red line is the TIN line and the green is the 2D arc. That setting will adjust the space shown here.

A good start for setting the distance number is 10 feet for small sites up to 10 acres. We move to 20 feet when things get larger than that to keep a good surface size. There are instances where you will need to adjust this but this is a great place to start.

Surface Review and Detailing

When you have a surface that looks good to you there needs to be a way to check it. You need to look at the appearance as well as the performance. Let’s first look at appearance.

Surface Appearance

To get paid at the end of a project, an owner must be satisfied with how the job looks. We have all seen poorly performed jobs that look great. Commonly the issue is that the performance faults appear after a crew has left an otherwise good-looking job. Depressions and bird baths in parking lots. Incorrect paving base depths and respreads thicknesses all take time to manifest and tarnish the overall appearance of a job.

The easiest way to see how a surface looks is to contour at a tenth of a foot interval. Subtle grade changes become obvious and draw your attention to the areas that need attention. This image shows good transitions and will not surprise a fast driver at the entrance.

To verify how the water is going to flow, turn on the slope arrows for confirmation of how water will flow when it rains and snows.

Take a close look at the parking stall in the northwest corner. There is a grade break at the south end of the parking stripe moving water to the northeast and then joining the sheet drainage to the southeast. This looks a bit odd but keeps the water moving out of that corner.

You also need to look at drainage areas. These areas need to keep water moving in the right direction and can also be used as common areas and playground facilities. The potential use of drainage areas varies without a lot of ADA requirements for slopes due to being primarily drainage. Be sure to review contours and slope arrows for correct directions.

Surface Performance

Now that the surface looks good, it’s time to verify the performance. At this point contours are not necessary, but I like to keep slope arrows on while moving around the project. I will go over this in the accompanying video. When reviewing a job at this stage, these are the things I look for.


We usually don’t do much in data for the areas outside a building. When concrete is installed and grading is performed around a building, the GPS signals are blocked and the work is done with smaller non-controlled machines. In any case, make sure there is drainage outside the building envelope per plan. We often see 5% slopes for dirt outside the building.


Any sidewalks outside the building as well as common area sidewalks need to be at no more than a 2% cross slope. We have some clients that have us slope to 1.5% for a margin of error to not exceed the maximum. Trail looking sidewalks are common in drainage and park areas, and sometimes have vertical alignments associated with them. These types of mini-road jobs need to be looked at where the alignments and sidewalk are treated like a roadway. In my experience, this is the best way to work through them. It may take a bit more time but it’s worth it.


After reviewing the contours and slope arrows we can confirm the surface will drain. This is the time to make sure the paving is done correctly. A big debate in our industry is the production of subgrades. I don’t mind having software build subgrades for a takeoff, but I don’t like to use them for production. The crossing lines and vertical jumps in the surface can affect a blade as well as not being sure that they are in the right place. A few inches thick paving on a takeoff is okay but will result in phone calls if it makes its way to the model.

We recommend dialing down in the machine or rover to get to subgrade. The fact is you must have the presence of mind to either load the correct surface or dial down. Either decision takes thinking it through and attention to the details. We don’t feel we need to spend our client’s money for building subgrade surfaces when field dial downs are better. Here is why. I can dial down to get to top of dirt in a parking lot, then pick the back of curb line and do a 3-foot offset to get to back of curb with room for the curb machine. Focus the 3D on the other blade tip and the parking lot slope will be projected to the back of curb. That surface cannot be made easily in the office and is quick in the field to accomplish.

There is a process we go through when producing site data and is tweaked by each of our engineers to suit them. Come up with your own process and stay with it. Productivity increases when you know what you have done and what comes next.


What to Expect from Free Models

What to Expect from Free Models

Being offered a free model to work from could potentially save time. You may even think, “Why not?” In this post, I will discuss what’s entailed when working with free models and how to determine the best approach. Use this as a guide on how to look at a model you’re given and verify that it’s what you want. I’ve outlined a process to make it easy for you to verify if the data is ready for the field.

The Surface

Most of the time when you are offered a surface file, it’s something the engineer has produced. The quality of the surface file can range from “ready-to-go” to just useless. Two explanations could be the engineering firm may have built the surface file to be used in dirt calculations (takeoff surface) or created the file for a presentation. You will not want to use either one.

The Takeoff Surface

When providing numbers for permitting and dirt use, the engineer will make a surface file. For the purpose of a takeoff, it does not need to be exact. I have long stated that if you use your takeoff surface for data, you’re spending too much time on the takeoff. Another more important reason to be wary of an engineer’s takeoff surface is that it’s generally done at the first draft of the site. Comments from agencies, owners and the utility investigation will make changes to the plans that affect the surface rendering making the takeoff surface unrelated to the final plans.

The Presentation Surface

More engineers are using 3D design to produce better projects. A 3D model gives the stakeholders a better idea of what the finished job will look like. When the vertical components (e.g., buildings) are added, the improvements made to the appearance and function are easier to see and quick to update. As the design matures and gets in ground stage, 3D model updates usually stop and the focus switches to printed plan production and permitting. This is understandable and normal in the paper plan world we still live in. It will take many years for 3D models to become part of the plan submittal. In post approval, we see highway projects requiring 3D model submission for approval before paving. Civil sites are not there yet.

Surface Review

When you receive a surface file, there are several steps to confirm if it’s even worth loading in the rover. Time is money and it generally takes longer to review a surface file than to just start from scratch. To use a surface file, you’ll need to take the file apart and then reassemble it to verify it’s accurate. This will take almost double the time versus creating the file. At TOPS, we never use an engineer’s surface file for data. Our clients ask us to make it for them.   The following is the process I use to review a client surface file:

  • Inspect the file size. A surface file may be big because it represents a large area. I often see smaller surface files that are too dense and contain a lot of unneeded triangles that are hard to remove or filter.
  • Determine whether the surface is dense enough. If the triangles of the TIN are spaced too far to indicate correct details this affects accuracy. The file may get you through rough grade but a better one will be needed for finish.
  • Confirm the version. Many times the surface file is used for one of the purposes I outlined above and is an older version of the plans. We see this a lot. A quick way to tell is to look at the deltas on the plan revision box and see what type of changes happened since the file was prepared.

When the surface file has passed the above inspection, it’s time to review the quality of what you have. Be aware that any review and work you do short of a full build of the surface file can still mean problems. Be cautious.

Review Process

Always start with the most difficult parts of a surface file to model. I’ve outlined what to look for on the different project types, as well as, Field Model Requirements that can require models built for surfaces other than finish.

Civil Sites

  • Look for flat building pads and smooth sidewalks from there to the curbs.
  • Go to the parking lot and verify the storm rims are correct and look at the slopes to them. Are they smooth and in the correct direction?
  • Entrances and exits need to match up to the existing pavement. This is usually finalized in the field. Just look for big discrepancies.
  • Finally, review the retentions and landscaped areas. Check the volume of retention against the called-out requirements in the plans. Often these must change during the design process.

Field Model Requirements

  • Pad Blowups
  • Subgrade surfaces
  • Paving overbuilds for curb machines and base

Urban Streets and Subdivisions

  • Verify the COGO (Coordinate Geometry) of the centerlines.
  • Check the cross slopes of the streets.
  • Review the intersection quality. Verify the details shown match the plans. If there are no details present, look for water movement and drivability.
  • Verify the sidewalk and parkway (e.g., grass) areas that are critical to slope.
  • Confirm the 2D and 3D properties of lot and pad dimensions.

Field Model Requirements

  • Gut section (over-excavation of streets for fill by utility spoils)
  • Subgrade surface
  • Matching roadways into field shots taken at sawcut lines
  • Utility trenches


  • Verify horizontal and vertical alignments.
  • Confirm roadway width. Includes widening and intersections.
  • Review cross slope and super elevated curve transitions.

Field Model Requirements

  • Widening base for track grade
  • Subgrade surfaces
  • Non-conforming subgrades, this is where the subgrade is not parallel to the road surface or the break point of the subgrade is not at the road centerline.
  • Catch points that need to meet a field generated topo

It is possible to use a surface from an engineer as a basis measure of quality. However, when the smallest doubt arises, it is best to build it so you really know what you have. 

Enhanced Data: Highways

Enhanced Data: Highways

There is nothing more difficult, or rewarding, than seeing a highway job perform well from dirt work to paving. It takes years of experience to fully understand the process. My advice is to think differently about the approach. In upcoming blog posts, I will go over the different approaches available for both Trimble Business Center and Carlson. These will be high level overviews of the enhancements we use for basic road elements. If you are a beginner, we will offer resources to get you up to speed.

Horizontal Alignment

The coordinate geometry (COGO) of a road, or construction centerline, can either be a quick data entry job or an enduring nightmare. Here is an example of a curve table. When things aren’t working with the parameters entered, you will need to decide what figures to pursue and leave the rest to tweak as you go. Notice in this example the PI has two (2) different coordinates. It’s probably a typing error and a clue there is a problem ahead.       The following is a list of troubleshooting tips:

  • Enter the PC, PI, and PT coordinates and stations first. Then enter per the plan.
  • Adding the delta and the curve will help resolve calculation issues.
  • Recheck the other numbers to see how close you are to discover errors.
  • You may not need to contact the engineer if the numbers are close. However, close is relative and a lot of bad curves can affect the length of a centerline.
  • When the centerline is a median, or other non-road geometry, offsets will need to guide the actual construction. Be certain the horizontal and vertical alignments are correctly matched in all three dimensions.
  • Not all field software can handle Station Equations. The rover can decipher the information while the machine cannot. The short answer is to make two files and overlap the data a few hundred feet so the operator can make fewer file changes.

Vertical Alignment

Vertical alignments are generally not as challenging as horizontal alignments. The most common issue is reworking an asymmetrical vertical curve. I’ve listed some tips below:

  • A road starting mid-vertical curve with no information for the PVC can either be scaled or some math should be performed to get the curve right.
  • Rehab profiles sometimes come without instructions for the new alignment. Rules need to be applied to the existing profile to identify the adjustments. The reason is when there is a mill and fill requirement, a survey crew will stake and set up the road. This should be done electronically. It takes more work since the alignment needs to be drawn or imported from a profile view in CAD. (I will describe this process in more detail in a future article.)
  • When encountering bridges, it may be tempting to ignore the vertical curves to save time. Always include them to troubleshoot design issues during construction.
  • The vertical is not always in the center of the road. Worse yet, it can shift during the job. Don’t be concerned about stopping and starting a road job at a station where this occurs.

Super Elevated Curves

Super Elevated Curves are not hard to understand. Where they are challenging is getting the standard details to match the cross sections and super diagrams. The transitions can also cause confusion. There are conflicting opinions on guidelines to use for Super Elevated Curves dependent on the state or country we are working in. The following are the general guidelines that we use.

  • Normal Crown
  • Runout is the length of roadway needed to accomplish a change in the outside lane cross slope from normal rate to zero.
  • Runoff is the length of roadway needed to accomplish a change in the outside lane cross slope from zero to a high side crown slope (usually 2%). Some explanations stop there and use this term to detail the rest of the transition.
  • Runup is the length of roadway needed to go from a straight cross slope percentage to full super.
  • A lot of state formulas are produced by transitioning some fraction of the curve length, usually by thirds. This diagram displays basic rules that many DOTs follow.
  • Note the axis of rotation, it can change and shift when super curves are drawn by engineers using older software. Also be aware of an old job that’s received funding and plans have not been updated.


Now that we have a good foundation for making a corridor, it’s time to attach templates to the alignments. I build roads planimetrically with as many pieces and parts required to get it right. Planimetric roads are a combination of templates and plan based features.

  • Driving lanes always require templates; at least in areas without intersections.

  • Intersections will require more data.

Using planimetric roads is advantageous when working with data that goes into the field, and is used by data collectors like templates to slope stake. Be sure to make a file that skips the staking plan details. The machines are fine with a surface. However, white paving will depend on brand.

  • Drainage elements, like ditches and culverts, are sometimes only available in plan view. They generally take a lot of time to calculate and make into a template element. Best to drop them on the screen.
  • The further you go outside the roadway, the less you need that data on the road file. Consider putting retentions and other out of bounds work into a separate grading file.


The basics are done. We have a road on the screen. It is critical to remember that we are only building part of the information on the plans. Any questions can be answered in the standard details provided by the agency. This is an example of a partial list of the standard details for a job. Questions can come up because the plans that are printed, and sent to the field, are abbreviated. There is usually no need to print the standard drawings, but if needed the drawings are easy to pull up in the job trailer. Everything from super elevation calculations to guardrail shoulders are there. You may find the plans do not reflect the standards in some areas. There may be an oversight you will need to fix in the model before going to the field.


A lot of money is earned by meeting specs for a rideability bonus. All roading software has a way to check for the IRI, (International Roughness Index). This checks the current profile as drawn in the plans. We will often see a profile that is very close to the desired index. In other words, if the road exceeds the drawn profile by a small percentage, the index will not be met. In that case we will recommend a value engineering profile adjustment that will give the contractor a better chance of getting the bonus without affecting the road. Designers will often get a profile drawn by software, the algorithms do not take rideability into account; we are just offering the owner a chance to get a smoother ride for the user. Contractors will often get automated paving equipment paid for in a bonus depending on the size of the job. This reinforces my advice to be sure the driving lanes are produced with templates. Everything from widening to supers are better generated with templates for the software to correctly transition these and other elements.


New hardware used in the field has capabilities that can benefit from the enhanced data from software. Terramodel and other previous generation tools did an adequate job but the data was not robust enough to effectively drive modern grading and paving equipment. Make sure you are giving the field the best possible information. There is usually a lot of money riding on it.  

Carlson Software and Working with Surfaces

Carlson Software and Working with Surfaces

Carlson Software is a very adaptable tool. It can run standalone by using the IntelliCAD engine or as an add-on to AutoCAD and Civil 3D. At TOPS, we all run Carlson on top of Civil 3D. In my opinion, this provides a robust, versatile work platform.

In this blog post, I want to review some of the commands that make surface production and checking easier for advanced users of Carlson Software. These commands will be useful after creating a surface that includes 2D lines, 3D lines and points.

Surface Production

A surface can be a combination of 2D lines, 3D lines and points. The following outline is a good process to organize these elements:

Layer Naming

  • Use a layer naming convention system and stay with it. At TOPS, we use different conventions for clients based on their needs and history. Avoid confusion by standardizing your conventions.
  • Be sure that anything used in a surface starts with “3D” in the layer name. This helps simplify your convention so you don’t miss something on a surface that is not included in the model.
  • To go a step further, use a layer state with just the 3D layers to make sure you are building with all the correct elements.

Above is an example of the elements used in a surface.

Initial Surface Build

It’s common to initially build a surface by fixing the obvious mistakes in order to get an idea of what needs to happen to make it perform correctly. But, it’s important to remember that the surface must meet the engineer’s intent and make a moving blade cut good base for paving and buildings. Here’s a suggested process:

First, decide on the layers necessary to make an initial surface. Understand that you may not draw breaklines or added spot elevations at this stage.

Second, open the Triangulate and Contour command and populate the settings preferred for the surface. Here are some suggestions:

  • I like to initially see the faces to watch how things tin.
  • When doing an FG surface, try to make a boundary. Shrink wrap is okay to start a finished surface job or for an OG topo. Get a tight boundary before sending to the field.
  • Prefix Layers With Surface Name adds the name for the surface to all layers used. This is an efficient way to set all the layers in one spot.
  • You can adjust the Triangle Length but I prefer to let the program make the surface then add breaklines to control length.
  • Densify Breaklines is a great feature. It will add vertices at a specified interval, like densifying a polyline without the mess during production.

  • Draw contours for a check.
  • Run Contour Intervals at .1 feet to get an idea of surface integrity.
  • Don’t label contours for this step in the process.
  • The Selection tab allows you to pick the element type for the surface. This may help if you have un-needed element types residing on a data layer. It’s best to have layers with only types you want and not rely on selection types.

Here is the initial look at the surface:

Even with contours at a tenth of a foot, this surface does not have a lot of change in elevation. There are things we can do to make it perform better and it will be good to add breaklines in order to improve things.

When adding breaklines, the goal is to make the surface perform well when paved but more importantly it needs to work well with a grader blade that is tasked with smoothing things before paving.

This task takes practice and experimentation. There are no easy formulas to follow. Experiment and keep a good line of communication open with the field in order to get things working right.


After the first surface generation, I will add breaklines to the surface to make it look and work better. To apply this practice, I’ve outlined some general guidelines:

  • A breakline is nothing more than a 3D polyline. It can be generated by the software or added by the user. It’s named because it forms a grade break in a surface where it did not exist before.
  • People use too many breaklines. Don’t be afraid to try something and then delete it if you don’t like it. An example is included in the accompanying video.
  • Use the same rules for breaklines on the entire project. If you do work to make one island work, do the same changes to the others for consistency.

Here is a quick look at the same area shown before breaklines. The grading is now smoother and sharp grade changes have been eliminated.

In the video I will demonstrate breakline techniques that will get you on the right path to make the surface behave the way you want.

Working with Polylines

The most difficult part of data prep is working with 3D polylines. The hardest 3D lines to make are those associated with curbs in parking lots. We need to respect crossing contour lines and spots along a line representing the edge of paving or curb faces noted in the plans.

When a single line is properly made, we need to offset it to make other 3D lines in relation to the first. If we generate an edge of paving line, we will offset to make a curb bottom then top, and finally top back of curb.

Base 3D polyline creation

In this example, I will elevate the edge of pavement line, then move it in 3-dimensions to make the bottom face of curb and top back of curb.

The Edit Assign Polyline Elevations command now has a real-time profile view in the command to help you visualize the resulting line.

This project has contours at .25 feet. That presents its own set of problems because high and low breaks are seldom called out. This requires us to make those grade breaks. Below is a representation of one of those locations:

Contours are at 81 feet with no detail near them. Without additional work, the street would have a flat spot at the paving edges.

Always contour the site at .10 feet so that these flat spots will become obvious.

Once corrected, the surface will start to look better and perform well.

After creating a 3D line that represents what you are after, it’s now time to offset that line to get what you need. Open the Offset 3D Polyline command.

This command has great chops! There are a lot of variables in the radio buttons. I urge you to review and get used to them. For this requirement, I will use the multiple options.

The Change Layer option can be used for the other commands. There will be layer options in the next window.

With this window, we have a lot of options. I need to point some out for the best results. The Progressive Offsets checkbox takes the new line made in the next row. It makes the change to it and not just he original line being offset multiple times. We want to use that here.

We do not build curb this way. I am doing this as an example of duplicating a fill gutter and related curb elements. With the paramaters set, click OK and pick the lines you want to work with.

A quick look at the new lines in cross section show the gutter and curb details. This would not work for a grading file, this is just a good representation of what the command can do. We run the paving slope out to the face of curb then go to the top back of curb.

The command will also work for a quick pad stepdown or a blowup to get pad limits for slab prep.

The command is also useful for a simple entry road. The command will perform the change to the centerline on both sides giving you a quick roadway.

Another advantage to the command is that it will place the new lines on a layer of your choosing. At TOPS, we like to segregate 3D lines as much as possible and this command does it for us.

The Process

With the ability to create a surface and tools to adjust things, you now have the ability to get closer to what is required in the field. I say our work is 90% science and 10% art. It does not take years to get proficient at building data. However, do pay close attention to every step and the outcome of your actions to a surface. This will help you to get better faster. Focus on areas that need work initially and then step back to be sure everything works together as a good, performing surface.