Civil 3D Best Fit Questions

Tags alignment, profile, best fit, Profile View, survey, survey figure, figure

I often get variations of questions surrounding Best Fit Alignments and Best Fit Profiles. Both are really useful AutoCAD Civil 3D commands particularly when you have gathered Survey data and must supply something that delivers and documents the real world. One of my favorite questions:

How am I supposed to create a Best Fit Profile?
The command line asks to select a Profile View, but I don’t have a Profile View yet?

I’ve been known to brain freeze too.

Create One

Dooh! We sometimes get mentally stuck on our common habit of creating a Surface Profiles first.
You don’t have to.
In Civil 3D you don’t actually have to have a Profile Feature (or a surface for that matter) to create a Profile View. However, you DO have to have an Alignment to hang the Profile View on. Civil 3D always collects Profile and Profile View Features into one of the Toolspace Alignments collections.

 An Empty Profile View

The Best Fits are a fast way to create horizontal and vertical control for existing shot data. Suppose you have Centerline shots or manhole locations. It’s easy to pump these into a Survey Db using the Survey Import Data wizard. Hopefully you’ve also got a Figure Prefix Db that will Process Linework and create Figures from the point descriptions in your Survey Db Network.

Remember in Civil 3D you DO NOT need (or WANT) any points or figures in your current drawing a lot of the time. In Civil 3D we get access to the Survey data selectively. Yippie!
This is one of the really good and different things about Civil 3D Survey.
There’s no need to be buried in currently useless stuff.

In the Survey Toolspace, perhaps you end up with a list of figures that look like this. Note the CRN1 figure.

 Figures in the Survey Toolspace

Only Create Specific Selected Points

In our current scheme this Figure represents centerline shots. We just want the POINTS related to that one specific CRN Figure in our drawing.
Survey can do that?
You betcha.

Select the figure in the Toolspace, Right Click (as always), Pick Points>>Insert into drawing.

 Survey Points From Figure

C3D will create ONLY the COGO points related to the Toolspace selected figure. Way Cool.
Yeah. I turned on some Point labels from the Jump Platform Style collections in InstantOn Basic to show you something in the picture. I wouldn’t do this normally. Ok. Maybe I might employ an autoscale Point Style assigned to the ever present default Point Group.

Maybe you want a couple of other specific points or points from another figure thrown in too. Just repeat the process from the Figure or the Survey Point collection as required.

The AutoCAD Civil 3D Best Fit engines will work off collections of PAIRS of Input data as well. In other words, they'll find the chewy center(s) between two edges. If you use map like primitives this will require some Weeding which is built in where needed.

In our SIMPLE centerline example all our points will be in the _All Points Point Group.
You may need to manufacture Point Groups to collect the right and left points into two different Point Groups, if you are generating centerlines from right and left flowline, curb, riverbank, or canal shots.

Maybe I should digress for a minute and talk about agricultural, archeological, recreational and other useful  applications where this set of Civil 3D control building tools come in really handy. Nah.
The smart and attentive folks can make themselves new business in a bad economy all on their own.

Create the Best Fit Alignment

The command is simple enough.
Pick your Kind of Input data poison - There are lots of kinds available besides COGO points.
Decide on HOW the point data will be evaluated by the regression analysis engine.
The important trick is to KNOW what types of alignment or profile segments are allowed for the data in question. If there can’t be a spiral or a curve in the results uncheck the boxes and/or set the curve radius value to “0”. Those settings get you only tangents.
Often I’ll simply start with all tangents to check on the regression results to see what I have to deal with. This typically will create a basic "frame" around which curves are potentially constructed in follow up passes. 
Undo is your friend.

 Create a Best Fit Alignment

Regression Analysis Screen

 Best Fit Alignment Report

Don’t forget to turn on the results screen (the Show report checkbox) and look at the results. You can select one or more evaluated points too and get some basic interactive feedback in the graph.
Note that you can copy the results out to the clipboard, a text editor, and into an MText object for that matter. I tend to only pump out my “final” results after more than one pass, but you have to do it NOW before you dismiss the dialog box. There is currently no way back to the results page post Best Fit creation. Like I said, Undo and repeat is your friend.

Create the Best Fit Profile

Create a Best Fit Profile

I already commented on the Profile View creation procedure that may cause a stumble.
Best Fit Profiles is a slick way to pull basic vertical design control from existing and/or intermediate design surface data too.  
Pay attention to the Input data list and the interactions with Weeding parameters. 
By “intermediate design surface data” I mean a surface built from other Civil 3D Features that helps you get from A to B. For example you need to create a standard 2% grade. Classically this is one surface built from a preliminary corridor (Yeah even a Grading Group works) that used to create the control for yet another surface and/or corridor control element. Corridor Baselines are by definition Alignment –Profile pairs. I trust the tie in is intellectually obvious.

Best Fit Profiles gets you to a simple but effective “matched to A” results solution faster and with more repeatable results.

All is Not Ordained

Once a Best Fit command is run you should check and often edit the results. The generated control Feature is NO LONGER related to the data it came from. Just because a Best Fit command spits it out doesn’t make it “right” of course. That doesn’t make it “wrong” either.  It’s useful. Some cleanup is often in order.  
Check the results in the Geometry Editor of BOTH Features for reasonable results. For example - a roadway alignment curve radius that’s 374.722’ you might consider “fudging” to 375’ - That may be a city standard. You check that stuff don’t you?

Geometry Tweaks

We should also note that both of these commands obviously assume tangency when constructing curves et al. That isn’t always the way the real world is as we all know.
However, these days inside Civil 3D we can much more easily edit the results in more ways. The commands also must evaluate things in one “starting” direction “up” the data. This may NOT be the direction you EXPECT. Often it isn’t. An Alignment Reverse is in order.

AutoCAD Civil 3D release 2012+ tangency constraint editing functionality made both of these commands more userful as it is now far easier to rearrange the results into something more useful without a wholesale rebuild and do over. Oops. That assumes you have learned how to do that and use 2012 or 2013. Forgive me.

Hold on There

Currently, the neither data points gathered  and/or regression results can be weighted  - Hold this point NOT those other points. This might indeed be handy, but you can always make it so after the control is built anyway. In other words, the non-weighted results are NOT a reason NOT to employ the commands. I heard this objection from someone one day not long ago, so I thought I’d mention it. Both tools are often better and faster than a trial and error construction method without any quantitative support.

Autodesk tested a cloud based solution this year with support for more complex algorithms and off loaded compute tasks. Now that promises to maybe raise some more interesting questions.

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