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## How to generate 3D surface with a mathematic expression?

AutoCAD 3D surfaces can be created also parametrically - generated automatically using a math expression (equation). For this you can use the free application CADstudio 3DPlot.

In your current DWG drawing, 3DPlot generates a 3D surface of the type polyface mesh by applying your custom defined expression, entered as [X,Y,Z] = f(U,V). So you can generate eny mathematic surfaces. The 3DPLOT command contains several sample objects.

To use your own math functions (after you load 3DPlot), you need to perform two steps:

2. call the tool (3DPlot) to plot it.

For an example, a 3D surface defined by the expression Z = sin (2 * x * y) will need these two steps in the following form - enter the LISP commands in your AutoCAD command line:

```
(defun mySaddle (x y) (list x y (sin (* 2 x y))))
(3DPlot mySaddle -1.0 1.0 0.1 -1.0 1.0 0.1)
```

The first line defines your math expression to a LISP function "mySaddle" (must return a list of coordinates X Y Z). The second line then calls the plot engine for points in the interval (-1;1) in both directions, in a step of 0.1. The result will be a nice 3D "saddle".

The top right image in the DWG format - see Boy surface.

 See also: Tip 11994: How to scale a 3D model to a given size in Fusion 360? Tip 11970: How to find the map coordinate system of a drawing? Tip 11939: How to extract pipe centerlines from 3D point clouds? Tip 11868: Open just a part of a DWG drawing - layers, views. Tip 11847: Automatic UCS aligned with the current View (UCSauto switch).