Creating a NURBS Surface from Topographical Contour Lines


Pt Bonita.jpg

Use Rhino to model topography in 3D to better understand site context, produce site drawings, and build site-accurate 3D models. The workflow requires contour drawings to create a NURBS surface by using the Patch command.
Uses Tool(s) Rhinoceros , NURBS Surface
Some or all of the information on this page is incomplete, incorrect, irrelevant or confusing. Please help clean it up if you are able.
This workflow is missing a general introduction and synopsis


Topographic Contour Lines in Rhino

Site plans or landscape drawings often have topography contours that relate to the change in elevation that occurs over the site. Depending on the site, the lines may reference a one foot change or a ten foot change. This tutorial shows you how to add a NURBS surface to the lines to help you visualize the site and create accurate site plans , sections , and renderings.

Contour Map_Flat.3dm

Moving Contours to Proper Height

In Rhino, the contour lines can be modeled in 3D space by raising or lowering them according to their proper elevation height. This task is simple but arduous, as it involves moving each contour line up in the correct increments. Each successive contour line will be moved up a specific increment depending on the spacing of the lines.

In this example, each line represents a one foot change in elevation. In Top view with Ortho on, select a contour line. Then, go to the Right or Front view and use the Move command to move the line up one foot. Ortho is required so that the lines are only moving vertically, not side to side. Follow the same steps for the next line, but move it up two feet, and so forth. Once all the lines are moved to the correct elevation, go to the Perspective view to see how the contours are starting to describe the site in 3D. Be sure that all the contour lines, including smaller plateaus or valleys, are either raised or lowered to the proper height. In Top view, the lines should look like they have not moved.

Define Your Site

The next step is to define the extents of the site. In Top view, draw a rectangle to denote the site's boundaries. In Perspective view, select the rectangle and use the Extrude command to create a rectangular box. Make sure that the sides of the box are long enough to encompass every contour line of the site extents. In Top view, using the Split command, first select all of the contour lines, then select the box as the cutting object. Then, select the unneeded lines that are outside of the box and put them on a separate layer for easy toggling.

Contour Map_Prepped.3dm

Define Border Edge

In order to create a clean NURBS surface , it is important to have a curve outlining the edge condition. To do this, first create a new layer for the border edge curve. Then, in Top view, select all of the contour lines that touch the edge of the box. Any curves that are only located in the middle should not be included. Use the Divide command to divide the curves by 1 so that each curve has a point at the end. It may also be helpful to place points at the corners of the site, using the rectangular site border as a guide. Select all the points and use the CurveThroughPt command. Make sure that the curve is closed.

Contour Map_Cropped.3dm

Create Surface

The Patch command requires a starting surface from which to start. Select the rectangular site border and use the PlanarSrf command to create a starting surface. Now, run the Patch command. First, select all of the contour lines in the site and the site border curve. Next, in the Patch Surface Options window, click on "Select Starting Surface" and select the surface that was just created. Changing the U span, V span, and Point Spacing will change the level of detail of the new surface. Press "OK" to create the new surface.

Contour Map_Surface.3dm

Editing Created Surface

The resulting surface may need some editing and trimming to make sure that the topography is clearly represented. For instance, if there is a dip in the surface where it should be flat, additional contour lines at the correct height will help ensure the Patch command creates a more accurate surface. Another option is to select the surface and use the Smooth command, choosing "Smooth Z." The greater the Smooth factor (which ranges from 0 to 1), the smoother the surface will be, which means that it will be less exact, but will read better for graphic purposes.

Contour Map_FinalSurface.3dm

Common Problems


RhinoTerrain plugin
This is another tool for exporting GIS data or contours into a surface model in a fewer number of steps. Helpful if dealing with a variety of surface models to expedite the process.