Comparative Civil 3D Surface QC

Tags surface, Style, TIN, survey db, InstantOn Survey, qa, qc

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 almost always get a question that runs something like this,

Is there any way for us to see what changes we’ve made to a Civil 3D Surface?

Quality control is everyone’s problem. Both Survey and Design folks ask this. 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 sometimes massacred.

If you must create validated surface and edit field work that includes lots of Figures, I can hear you squalling. There’s great news- Civil 3D can answer the question well.

The Edit Stack

Of course by now you’re recognized that every Civil 3D surface keeps an “Edit Stack” in the Surface Property Definition. This Good stuff - order matters to surface resolution.
The Surface operations Edit Stack is more than handy but that manageable exacting detail may miss the more mission critical questions that we frequently have to answer.

What did I do to the sucker?
Did I really get all the corrections and adjustment done?

What’s the Difference?

To answer the question we must first remember to keep a copy of the way it was. That simple task is often a somewhat difficult discipline to master. I suggest you build a Surface 2 Surface Comparison 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 way it was and the current edited version.

Another approach is to keep the “way it was” or “Start” Reference Surface available as a Data Shortcut and then check against that in the current surface drawing. You also need to also remember to clean up the current surface drawing after the QA is done.

Surface Comparision in the Toolspace

Create a TIN Volume surface between the Start Surface and the Current Surface. This produces a “Differential” surface.
No. We’re not looking for volumes but the results do and do speak volumes.
We can employ Civil 3D Surface Styles to visualize what’s happening.

This 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 InstantOn template and style library product we sell.

Show Me the Money

In the following examples the CURRENT surface is displayed as TIN triangles and points ABOVE the Differential surface displayed in a series of various Quality Control Surface Styles. Each Surface QA Style representation gives us different and useful information.

Comparative Surface Analysis

Where By Slope Comparision

Where did the work get done?

A simple Banded Slope (4 range) analysis shows you in simple red and black where you made changes. This example from the InstantOn Basic project dataset shows the added 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 has additional the additional flowline data added in by Feature Lines.
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.

What about the How?

How By Elevation Comparision

A couple of Surface property click’s later here’s the same Differential surface displayed as Banded Elevations (2D). This 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.

If you think about it for a moment, maybe some manual TIN line flips (used to solve one problem) may accidentally create other issues. I’d certainly play close attention to where there is green where I might expect brown and vice versa.

Contours and Arrows Comparision

In this view the Differential Surface is displayed in a Surface Style that employs small incremental contours coupled with Slope Arrows. The bluer the Arrows the bigger the changes made.
What we might not recognize right away is we 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.

Profile My Surface Changes

Civil 3D allows you to Profile the changes you made to the surfaces by location. Here we just employed a Quick Profile generated from an AutoCAD Line. We’re not looking at a roadway cross section. At the moment we’re displaying the Differential surface – how big a change happens where relative to the line in the Profile View. This Profile is a Rate of Change graph.

The Civil 3D diva can be mindboggling

AutoCAD grips make it really easy to move the line around and study specifics. We could build another Quick Profile View that instead displays both the Surfaces and the Cut and Fill between.

Can you really tie two different Quick Profiles to the same line in Civil 3D? Does that matter?

It’s a matter of Managed Style tools that 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