How to Create Large Terrain Models


My team and I trying to create an accurate terrain model of our site for masterplanning. Problem is the site is massive. Whenever we import the CAD topography lines from the civil engineers, the compute slows down, has trouble processing the information and crashes. Even if we get a mesh, the program lags.

We were able to create a simplified model that got us the general idea of the topography, but lacks some of the information.

Do you have any advice to to achieve a terrain model that is more efficient yet accurate?

There is an extension called Skimp. It can optimize models a lot, including terrain data. The hills will look just as good, but a lot of unnecessarily detailed faces could be removed.

Would you be able to post a link to a small example file? I could then try running it through Skimp, and you can compare the results.

How are you making the terrain model? If contours, they may need simplification which you can also do in CAD before anything. So you can see in plan when enough (or too much) simplification is done. Contour plans I get are often overly segmented, not always displaying real data.
Or if a TIN model is available, that might be simpler, fewer polygons.

It is contours. How do you simplify it it CAD?

I have a routine in my application, PowerCADD. I would think there’s some LISP in AutoCAD that does it if not a standard command. It would have to work in the x/y direction only.

My coworker used Skimp along with some contour simplifications done in Rhino I think. That’s where we started to lose some of the information. Maybe I’ll give Skimp another try.

@colin I can upload a sample file next week when I am “back in the office”

Thanks. When simplifying with Skimp you can look at an important detailed area, and when it starts to lose definition you could back off a bit. Hopefully you will have reduced the number of polygons a worthwhile amount.

Also, go to the View menu, Edge Style, Profiles, and uncheck it. Your existing attempts will become incredibly smoother.

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Exactly how accurate? And how large a site? Are the contour intervals more dense than, say, 1 m while the site is larger than, say, 1 km x 1 km? Are the contours splines before you import them into SketchUp? The importing might create an immense number of small segments - it might be safer to split them into straight segments before import.

The site is fairly large. Larger than 1 km x 1 km. The contours are 1 foot contours.

The lines are not splines, but polylines.

My background is in Landscape so I hear ya on needing strategies for working with large terrain models. There is an extension by SketchUp called ‘Simplify Contours’. This is done in SU rather than CAD.

Another trick is to break the larger site up into ‘tiles’ - kind of like the new Geo-Location imagery feature. That way you’re only working on a piece of the site at a time - if that works for your concept that is. If you provide the Contours CAD file, I can show you more specifically the process.

Edit: there are other ways to import terrain meshes beyond Sandboxing CAD contours… Unless of course you are required to work with those exact contours that is.

This might lead to millions of faces/edges. Do the polylines have arc segments? I don’t know the logic behind the workings of the Sketchup DWG importer but sometimes it produces an insane amount of edges on arcs that are part of polylines.

I don’t mean to butt in on your procedure, but over a square kilometer do you really need 1 foot intervals? I’ve used this for house pads but have really wondered if it makes any difference. In general I believe surveys are only an approximation in the first place. Every point on those contours was not measured. If you use toposhaper or similar method to create the faces, you control the end resolution of points, and they’ll be another approximation.

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