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Civil 3D Surface Compare

Tags surface, Surface Style, analysis, Project Management, implementation, grading, corridors, video


Let’s face it - Surfaces play a huge role in civil engineering and survey work. When I train people in AutoCAD Civil 3D surfaces I frequently get this question:

“Is there any way for me to see what changes I’ve made to a Civil 3D Surface?”

First things first. Did you visualize the surface with at least 3 different Civil 3D Surface Style Tools?
I make no bones about this. Finding surface issues is an experiential skill in Civil 3D.
It takes practice to train your brain to see problems in a sea of dynamic data. Why we get paid the big bucks.

Surface Quality Control

Quality control is everyone’s problem. Both Survey and Design folks ask this question. Whatever you gather in the field it’s probably going to take some tweaking. Certainly whatever you design is going to be massaged, manipulated, and sadly sometimes massacred.

If you must create validated surfaces and edit field work that includes lots of Figures or a design surface with lots of Feature Lines and/or Complex Corridors, I can hear you squalling out there in Civil 3D Land. There are What, Where, and How questions to resolve…or not.

There’s great news is Civil 3D can answer theses question pretty well. Better yet it doesn’t take all that long to do once you master these Civil 3D Skills with Thrills.

The Edit Stack

We all recognize that every Civil 3D surface keeps an Edit Stack in the Surface Property Definition. The Edit Stack answers the “what’s in there” question. All TIN Wizards recognize that order matters to surface resolution. In Civil 3D we quickly discover that we can change and manage that in the Edit Stack. Awesome.
The Surface operations Edit Stack is more than handy, but that manageable exacting detail may miss the other more mission critical questions that we frequently have to answer.

“What did I actually do to the surface?
Did I really get all the corrections and adjustments done?
Did my fixes create other unseen surface problems?”

What’s the Difference?

The neat trick is to employ the Civil 3D Surface Style Tools differently on a Differential surface. To answer these questions we must first remember to keep a copy of the way a surface was. We cannot ignore the Arrow of Time. Good News. The Edit Stack may give us a chance to go back in time with a copy.
I acknowledge that simple task is often a somewhat difficult Civil 3D user discipline to master. When being the operative word.

  • What if I can build dynamic surfaces dynamically linked to the on-going edits to my Survey Db?
    See the Quick Surfaces from Survey
  • What if my design corridor is producing dynamic Feature Lines?
    Do I now have the capability test versions of DREFed corridor surfaces?

Let’s not get lost in Civil 3D techno coolness. Most of our surface checks are often simpler than those situations.

Build Surface Benchmarks

Project management in the Civil 3D Dynamic Model is a user discipline. We must choose to create and maintain benchmarks in our project development process. Civil 3D is not going to do this for us. Civil 3D has a number of built-in tools to aid us. All of them are about managed Data Shortcuts in the end.

  • The Separation of Feature Powers principal is important to observe from both project sanity and project performance perspective. If you don’t maintain the Civil 3D user discipline do to that, both sanity and performance will suffer when you are under pressure to deliver.
    See the infamous Civil 3D Features Matter Most
  • A structured set of Data shortcuts are central to a successful benchmark system.
    Autodesk added folder capabilities to Data Shortcuts for a number of reasons in 2017+.
    The ability to build a folder name plan that includes your benchmarks is an important one.
  • Employ a publish metaphor for benchmarked Civil 3D Features like Surfaces, Alignments (and their many children), and now Corridors.
    Use published LandXML versions of the surface (from any source) for project DREF consumption.
    Keep the construction drawing originals with inputs and results offline and elsewhere.

About Your Civil 3D Project Template

You might build a Surface 2 Surface Compare drawing in every project. Civil 3D Data References will automatically update the drawing for you once you get it set up. It requires two Reference surfaces – the start surface and the current edited version. You can chose to prototype the resources as Placeholder Features in your Civil 3D Project Template. You use a Civil 3D Project Template don’t you?

Surface Step by Step Analytical Mechanics

The common approach is to keep the Start Reference Surface available as a Data Shortcut and then check against that in a current surface drawing. In that case, you also need to remember to clean up the current surface drawing after the QAQC is done. We make temporary surfaces to test other surfaces. User project discipline once again raises its head.

Simple First

You need both surfaces in the drawing. At least one is best a DREF. Both surfaces should have colorized Triangles and Points surface Styles in complimentary color schemes. The basic difference in color should clearly show you the differences between the triangulations. We can do more.

Create a TIN Volume surface between the Start surface (usually a DREF) and the Current surface. The Current surface may be a DREF or not. There are good reasons for both approaches.
This produces a Differential surface.
No. We’re not looking for volumes. The Surface Properties>>Statistics tab shows this as a matter of course. You always check this tab?

Civil 3D and you can make the Differential results speak volumes.

We can now employ various Civil 3D Surface Styles to visualize what’s happening. That assumes you’ve got the Civil 3D Styles tools around to do this. Surface QAQC is vital and mission critical. We build QAQC Styles for many Civil 3D Features into every Civil 3D template and Civil 3D style library Framework for Civil 3D product we sell.

Show Me the Work

In the video examples the Current surface is displayed as TIN Triangles and Points in the Display Order above the Differential surface displayed in a series of various Quality Control Surface Style Tools. We are visualizing two (2) or three (3) surfaces at the same time. Our start surface could be Invisible. Each Surface QAQC Style representation gives us different and useful information.

Comparative Surface Analysis

The significant benefit is that none of this takes all that long to do nor is it hard to accomplish.
Practice makes better performance and better surface QAQC. Do the do.
The range themes used are not really kind if you have forms of color blindness. So edit the Styles.

“Where did the work get done?

A Civil 3D Banded Slope surface analysis of the Differential surface nicely does the trick.

A simple Banded Slope (4 range) analysis shows you in simple red and black where you made changes. This example from the InstantOn project dataset shows the results of breaklines derived from the Survey point and figure data.
In the field only the Back of Curb was shot for a “standard” curb and gutter.
The finished EG surface therefore has the additional flowline data added in by Feature Lines back in the shack.
The blacker the triangle is the more the Differential surface has changed. This analysis answers the question where you made changes and the equally important fact of where you did not.

You can generate a color DWF out of Model space if you want to track and/or markup these changes over time. Autodesk Design Review can be a functional auditor for Civil 3D projects.

“How Did I Change the Surface?”

We answer that with a Banded Elevations (2D) analysis of the Differential surface.

A couple of Surface property clicks later the same Differential surface is displayed as Banded Elevations (2D). A simple 6 range view coupled again with the resolved final EG TIN model shows in darker shades of brown the lowered changes and in brighter shades of green the raised modifications. DWF it.

Before the Post Mortem

I’ve got to say it.
Sometimes it pays to use a Differential analysis like this while you tweak the surface. You get better feedback. If you think about it for a moment, maybe some manual TIN line flips (used to solve one problem) may accidentally create other issues unforeseen surface issues. You should certainly play close attention to where there is green where you might expect brown and vice versa in this Banded Elevations scenario.

Rethink the Classic Slope Arrows

In lots of videos here you’ll see we employ Slope Arrows to validate design surfaces from corridors and the like. We can employ this classic QAQC Surface Style Tool with a twist on the Differential surface.

Copy and modify the Style tool or employ the classic Framework Cut and Fill style tool to employ small incremental contours coupled with Slope Arrows on the Differential surface.
The bluer the Arrows the bigger the changes made.
What you might not recognize right away is you can employ changes to the Datum properties of the Differential surface to control which contours are generated and displayed.
Show me all the ups but not the downs for example. DWT it.

Location matters…

Build a Quick Differential Profile?

Civil 3D allows you to Profile the changes you made to the surfaces by location too. Employ a Quick Profile generated from an AutoCAD Line on the Differential surface. This is not a classic profile. We display the Differential surface to help us visualize how big a change happens where relative to the line in the Profile View. This form of profile is a rate of change analysis graph.

The Civil 3D diva can be mindboggling

AutoCAD grips make it really easy to move the line around and study specific sections (pun intended) of the surface(s). We could even build another Quick Profile View that displays both the Surfaces and the Cut and Fill between.

It’s a matter of Managed Style tools that help you produce a more Managed Dynamic Model.

Stare and Compare

Civil 3D can do this Comparative Analysis pretty well. Our real world problem is that it takes some time, skill, and experience to learn how to read the tea leaves. This is a learnable skill. If you practice, you learn to see.

I personally find the most amazing thing is that people can see and practically employ this useful stuff without the faintest clue about how the math behind gets done.

Our Brains Do Make Order Out of Chaos