How to flatten curved lines while keeping proper lengths

[Anonymous]

Hi Yall,

I'm have a hard time wrapping my head around this. I used a photogrammetry software to capture to create 2d templates for production product. Up until now everything has been on a relatively flat surface and there hasn't been a need to do this.  I need to flatten these lines, but i need to keep their true lengths as they are when not flat. I have tried the obvious flatten command but that does not seem to keep the true length. I come from a solidworks background so trying something like this in AutoCad doesnt compute in my head. I also have tried to import my file into Fusion 360 but it seems to not like 3D polylines and they wont import in. If anyone has any helpful tips or can point me in the direction id be forever grateful. I've attached my current file for anyone that is curious.

[leeminardi]

The red line in the image below from your file is a 3dpoly. 

Using three vertices that define it I defined a UCS and then went to front view which yields the following image.

This image along with the results of using the list command show that the 3dpoly lies on a flat plane that is skewed with respect to the world ucs (I've isolated a few of the other 3dpolines and colored them green as a visual reference).

The question is, what do you want to do with this 3dpoly?  You can use 3dalign to reposition it to the world xy plane and not change the lengths of any of the segments.  But do you want to do that for each 3dpoly that lies on different 2D planes? 

[Anonymous]

Lee,

Thanks for the reply. My end goal is to lay everything flat on the same plane while keeping correct lengths. Ive tried FLATTEN command and that would work if it took into consideration the entire arc of the project. If i was to recreate this project after flattening it, parts will end up being to short due to how flatten just projects it flat without taking the entire curve of the project and adjusting.  

[leeminardi · Accepted solution]

Examining the geometry it appears that it almost lies in a cylindrical plane.

 If so, you could take the ratio of L (the length measured along the cylindrical surface) divided by LF (the length of the flattened geometry) and scale the flattened geometry by that amount in the direction of the curvature.

Note, L could be approximated by getting the length of an arc that duplicates this profile (I get 192.02), and L is the just distance between the arc ends (191.81).  The ratio L/LF is  1.00109 or about a 0.1% difference.  Scale tha flattened geometry by 1.001 in the one direction. 

[Anonymous]

Lee,

Thank you! I had a feeling i was going to have to go down that route, i was curious if there was a command in autocad that would do it for us lazy types. Anyway thank you for taking time and working with me on this.

Tucker