Create a Better "Best Fit Alignment"

[DenverDavid]

I want to create a best fit alignment for a stream channel. Unlike a road that one might "best fit", the channel survey points can have some sharp turns. when i try to best fit the points AutoCAD over simplifies the alignment: cutting out important curves, making curved sections linear, and so on. I am trying to figure out how to tell auto CAD to decrease the regression and find a more exact fit. Can anybody help me with this? I am using Civil 3D 2012 (and/or 2013 if it helps).

To be more exact, The Blue line is a pline of the surveyed stream center, and the red is the Alignment that was created. The Red needs to stay between the White lines.

[MikeEvansUK]

Do not create a best fit alignment. Create a new alignment and manually construct best fit entities to fit / suit.

[rl_jackson]

I would have to agree with Mike, although I might still use the Best Fit line and curve commands to suit the situation, and construct things as I moved down the stream. I would do the same thing with a road.

I this manner the alignment is your descision not just some answer that is calculate to some ninth degree that you have no clue on how it even comes into being.

[DenverDavid]

Mike Evans,
Thanks for the tid bit; breaking the line up into smaller segments does help produce a more exact "best fit". This may be a reasonable work around.
However I am still hoping there is a way to influence the best fit algorithm. If there is not currently, this is a feature that Autodesk should consider adding. I don't need the significant level of detail/control that building it manually would produce, just a slightly higher level of detail than what algorithm is currently producing.

[MikeEvansUK]

David, have you tried adjusting the weights of the control points?

This would probably do what you are asking for.

The knack is to select many control points and weed them out later adding some as passthrough points as nessesary as well as adjusting the weights of others.

It's trial and error really.

Can't help with the algorithym. You could program your own I supose.

[DenverDavid]

How do you do this?

[KirkNoonan]

It sounds like you don't want to construct it by connecting the dots to save time? When I have to do long pipeline alignments, I use excel to sort my points by northing or easting and number them sequentially in that direction. You can put the editied points back into your drawing and instantly create a polyline or feature line by point number range. Create an alignment from that, and you're done. The whole process takes less time than using the best fit command.

Kirk

[DenverDavid]

No, that's not what I am trying to do. I want an alignment with tangent curves and simplified through the "straight" sections and such. Not just connected dots. But thanks.

[MikeEvansUK]

See attached, assume you mean weights.

in image: Top, weights all set to 1. Bottom weights different and produce different result.

[DenverDavid]

Yes I would like to know how to  change the weights for different points. Where do you get the dialogue box that you show in the picture? Where do you change these options?

[MikeEvansUK]

When you create best fit alignment entities (edit alignment command).

Click best fit curve etc click on screen points then enter, the prospector should pop up and show these settings. You just edit the weights or pass through or ignore settings here.