Simplify Polylines and Create a Terrain Mesh from Existing Contours

Although our users can import contour lines for their area of interest directly from Plex-Earth, there are cases where these contour lines are produced from other software or local surveys. These contour lines can be very complex when transferred to AutoCAD, consisting of too many vertices. Thus, when Plex-Earth 5 is trying to process them, for example to create a terrain surface, it can result in AutoCAD slowing down or even freezing. As such a workaround must be performed for simplifying these polylines.

In this tutorial, the following two processes are presented:

a) How to simplify Contour Polylines by reducing the vertices

b) How to generate a Terrain Mesh from these Contour Lines

Part A: Reduce Vertices of Existing Countour Polylines

The process of removing the unnecessary vertices of a polyline is called "weeding". The feature is available in AutoCAD MAP 3D and in Civil 3D.

Below is an example of a drawing with contour lines acquired from a local survey.


If we select one of these polylines, we can see that it consists of breaklines, each one having a large number of points. This probably is already slowing down the CAD performance.


Moreover, if trying to create a surface from these breaklines, the number of triangles created will be quite high, thus resulting in CAD freezing.

Actually, if we zoom in more, the vertices of our contour lines will become obvious.


As such the weeding of these lines is the only solution for simplifying them.

In order to do that, we use the command "WEEDFEATURES" in the command line of Civil 3D and we select one of our polylines.

After, that, a window will appear, which shows how many vertices are going to be removed.

The vertices that will be removed, appear in red color.


Click "OK" for the changes to be applied.

Similarly, we perform the same procedure for the other contour lines.

tip_icon_small.png Tip: Instead of applying the command for each contour line separately, you can choose to weed multiple lines. To so do, after typing the WEEDFEATURES command, select "Multiple" from the command line and then choose your contour lines. Keep in mind that if your Contour Polylines are too complex, as the one shown here, choosing all of them at once, may freeze your CAD. Better choose some of them each time and then repeat.

If the contour polylines are too complex, we may need to apply the "WEEDFEATURE" command multiple times, in order to achieve the simplicity we want.

Below you can see the difference in a contour line, by applying the "WEEDFEATURE" 5 times.


After applying the process to all our contour polylines and as many times as needed, we can see that we can use CAD without encountering performance issues

So, now, we can move on to the second part and see how we can use these polylines in order to create a Terrain Mesh with Plex-Earth 5!

Part B: Generate Terrain Mesh from Contours

In order to Create a Terrain Mesh from our contour lines, we just choose "Create Surface" from the Plex-Earth 5 ribbon. Alternatively, we can type "PXV_TERRAIN_FROMOBJECTS" in the command line.


Now Plex-Earth 5 asks us to "Select Points". Since we do not have any points available, we skip this step using the space bar.

Then, we are prompted to "Select Breaklines". We select all the contour lines we want for our terrain mesh and press enter.

Moreover, we must "Select Boundary". In this case, the white line is our boundary, so we select it and press enter.

Finally, we are asked to "Select Holes", if any. We can skip this by using the spacebar again.

Plex-Earth 5 will now create a Mesh Object, using our contours, as shown below.


tip_icon_small.png Tip:  Enable the Realistic View for better visualization.


Creating surface models is very important in landscape and city modeling and for various other visualization purposes and design applications. With Plex-Earth 5 you can have the best of two worlds. You can combine the measurements of local surveys or data obtained from other applications and use them to create Terrain Meshes into your CAD software. With small processing in these acquired contour lines, you can overcome any performance issues and boost your productivity.


Feel free to contact us at for any questions you may have and don’t forget to start your free trial today.

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