Smoothen surface without affecting the edges?

Hi folks,

I have a question regarding smoothening topography surfaces, for a landscape architecture project, I’m currently working on. I’ll be projecting the otlines of streets, sidewalks and land parcels on a 3D topography. However - after dividing the topographical surface into certain segments, I’d like to smoothen/simplyfy the new surface areas, so that they’re not so uneven and ‘landscapy’ anymore. This, however, should occur only within the surfaces borders, so that the edges remain the same and still match the edges beside them.
What would be the best way of doing this?

I’ll be very happy to hear your advices,

Thanks in advance,

One thing to try would be to turn on the surface control points, and select only the interior points. Don’t select the point near the edge you don’t want to disturb, and use the Smooth command on the selected points.

Hi Helldoor- try the Smooth command with ‘Fix boundaries’ set, or, as John suggests, smooth only the interior points- what I suppose you will run into in either case is the trimmed edges not being controlled. Can you smooth the inputs? and recreate the surface?(points, mesh, curves?) If the surface is a Patch, you can make it using History and then smooth, if needed, some or all of the inputs, and have the surface update.


Your surface is a mesh? If yes you could use the Catmull-Clark smoothing from this tool. It should allow to keep the edges.


big thanks for the answer, John. The polysurfaces have a lot of control points and it will take a lot of time, but I’ll surely give it a try, as for the ‘Fix boundaries’ command (suggested by Pascal) didn’t really work out =[


Thanks, Pascal.
The Smoothen with ‘Fix boundaires’ didn’t really work out - after the second command execution (factor 1), the edges began to dostort.
As for recreating the surface - I could use DupBorder and after that Patch. But do You think, that several patches next to each other will still have clean and hole-free edge borders?


Hi Micha, nice to see you here and thanks for the answer. My topography is actually a Drape (I’ve been given a very bad mesh model, which I draped over). Therefore it’s a polysurface and not a mesh now. Do you think I should convert it into a mesh and try this plugin? And how about the usability of the meshes (for texturing etc.) afterwards?

Greetz to you all.

Hi Helldoor- what are the original inputs for the surface? And, is it made with Patch?


Hi Pascal,

it’s a polysurface - a result from draping over a really bad meshed topographical Height Model, I’ve been given.

Here’s a thought- ExtractWireFrame. Smooth the resulting curves in Z, with ‘Fix boundaries’ (the ends will stay on the original edge locations.) then Patch through the smoothed curves. Also, it may work to simply Patch (with History) then Smooth the curves only if needed (Patch may smooth things somewhat all by itself) and the patch will update. Note that multiple applications of Smooth with a small factor is generally better than few applications at a larger factor.


Thanks again Pascal,

extracting the Wireframe and smoothing it out did a nice job. It’s very useful for simplifying the internal areas of the topography. Patching, using the Duplicated Border works out also well, especially for the periphery of the model, as I can simplify (realign) the control points in the edge areas and then patch, using the rebuild border.

Tomorrow I’ll give all the methods you guys suggested a detailed try and post some results afterwards.

Thanks again and have a nice eve.

PS_ Wasn’t there a command for adjusting unfitting edges to eachother? That way one can simply patch and after that just adjust the edges of the single patches, so that in the end, no gaps are left. No?

Some years before I was working on a large terrain and I worked with a mesh. I used a planar projection from the top and mapped anything - grass, ways, sand … all in one material and visibility controlled by transparency maps at the different layers.

Hi Micha,

I had also thought of that, as I have been proveded with a HQ aerial photo… I’ll surely try it - out of curiosity =]

Update: gave the texture thing a try : it works perfect!

Now, about surfaces problem - the workaround I finally took is a mix of all your suggestions:

  1. I did cut the topo surface into topic areas (streets, landscape, etc.) using the 2D CAD Data as cutting lines
  2. After that I used _Smooth, selecting some inner control points (to save time and select only the controlpoints I wanted, I drew a curve around them and used the _SelBundary command)
  3. Despite of it however, the edges distorted a bit. To fix that, I used the _JoinEdge command on the edges of surfaces, located next to eachother. This command joins not only the Edges, but also the surfaces, so that no gaps are left. (to separate the faces from eachother, just go back to step One,)

That seams to work out pretty well. If you have any ideas in further optimizing the process, let us hear!

Thanks folks and have a nice day!

Hi Helldoor- see Help on JoinEdges. This command simply overrides the file tolerance for joining, it does not actually fix or move any of the underlying geometry. This is OK to force edges to be closed in order to get a closed mesh, or a nice picture, but otherwise, it can cause problems since the joined edges can be forced off of the surface.


Thanks Pascal, I’ll keep that in mind.