topic Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface . in AutoCAD Forum

Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

lucian.sandulescu — Thu, 27 Apr 2023 15:00:32 GMT

I tried to use the Flatten command but the area is not the same. How can i do it? Think about a sheet of paper from which I make a cone (3D surface) and then from that cone I want to have the sheet in 2D with the same area of the cone in 3D.

So, I design a boat, and i will attach the DWG drawing. I want that the surface near the boat to be in 2D that i can print like a model.

Can someone do it and tell me how and maybe can record the process. Please!

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

paullimapa — Thu, 27 Apr 2023 15:46:36 GMT

One way is to download free trial version of progecad and do that on there

https://www.progesoft.com/products/progecad-professional/manual?mp=drawing-in-three-dimensions/converting-three-dimensional-entities/converting-three-dimensional-entities-to-surfaces#:~:text=On%20the%20ribbon%2C%20choose%20Draw,then%20press%20Enter%20when%20done.

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

pendean — Thu, 27 Apr 2023 15:57:36 GMT

Your DWG file's content is spread all over the place (about 200-miles away from the 0,0,0 arrow

That alone may not be doing you any favors.

Are these the elements you need to flatten down to a single Z elevation?

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

lucian.sandulescu — Thu, 27 Apr 2023 16:04:19 GMT

I would like to make this in Autocad. as

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

leeminardi — Thu, 27 Apr 2023 16:06:07 GMT

The bottom gray colored surfaces of the hull are flat and therefore the align command can be used to place them on the XY plane.

The green and yellow surfaces are curved in all directions and therefore cannot be developed into a flat surface without some distortion. Think of how different projections of the earth are used to show its 3D surface in 2D.

Here's one way you might proceed to create a 2D shape of the yellow surface that has the same area as the 3D surface.

Determine the area of the yellow surface. Use the thicken command to turn it into a solid. I set a value of 0.1 and massprop shows a volume of 765.4567. Therefore the area is about 7655 units sq.
Note that the sides of the shape 1-2, 1-4, and 2-3 are straight. Side 2-3 is parallel to the XY plane.
From the top view create a polyline snapping to the vertices of the surface. This will create a 2D shape on the XY plane. The area of the polyline is 7014.92...
Since side 3-4 is the only edge that is not straight, it must have a curve to it when the shape is flattened. We also know that the keep edge 1-4 the same length, vertex 4 must be on the circle centered at 1. Create a single closed spline (green) as shown below. An easy way to do this to use osnap endpoint and the CV method for spline as follows:
click once at #1, click 3 times at #2 (this will create a sharp corner), click 3 times at #3, once at #5, 3 times at #4 and once at #1.
To get the area of the closed spline I found it easiest to hatch and then get then use area object.
Adjust the location of the CV near 5 to get the area you need.

I got the following for the final shape.

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

lucian.sandulescu — Thu, 27 Apr 2023 16:06:25 GMT

not all, just the second surface, the one below.

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

AVCPlugins — Fri, 28 Apr 2023 15:06:09 GMT

You probably meant that you need to turn the cone or cylinder onto a plane. There is no such command in pure AutoCAD, but there are plugins and scripts. Search for the word "Unfold". The free Unfold-scripts I found don't work very well, and the plugin costs ~$500. There are programs similar to AutoCAD and working with DWG files, which have a Mechanical version for working with sheet metal. Here it is quite possible to unfold solid parts (and probably surfaces too). However, you must have a part that can actually be unfolded, that is, a surface of the second order, and not a third (cone or cylinder). Spheres and NURB surfaces do not fundamentally have a flat development.

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

lucian.sandulescu — Sat, 29 Apr 2023 00:36:19 GMT

Thank you, can you please send me the file please?

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

leeminardi — Sat, 29 Apr 2023 01:12:03 GMT

Here it is. To improve the solution select the spline and move the CV at the bottom (#5) then hatch the spline to find the area. Rinse and repeat until you have the area you want.

Re: Convert a 3D surface to a 2D surface, but the 2D surface must have the same area as the 3D surface .

vladimir_michl — Mon, 02 Feb 2026 15:13:20 GMT

A little bit late but you might try the Mesh_Unfolder (free) with unfold and refold functions for 3DFace surfaces:

https://www.cadforum.cz/en/unfolding-of-general-polygonal-3d-meshes-mesh-unfolder-tip14889

Vladimir Michl, www.arkance.world - www.cadforum.cz