Creating Surfaces with Lofts – Example 4.4
Another common way to create surfaces is to use a tool known as the “Loft” These can be done in either Rhino or with Grasshopper, with the advantage that the Grasshopper surface is editable. The process for both is pretty much the same.
Process – This method might be used if you were designing a site through a series of site sections. In this example, I have drawn a series of four sections through an imaginary site. What loft does is it creates a surface that goes through a series of curves (open or closed). This concept is pretty straightforward but Lofts can get complicated especially if you are trying to have a surface go through curves that are not typologically similar, or with different numbers of Control Points, misaligned control points, or curves that are even drawn using a different method.
For the most successful Loft, all of your curves should have the same number of control points, and you should not mix open and closed curves. Select the curves in the order you want the surface to go through them. If you are creating your surface with Rhino you also need to be careful to select the proper end of the curve when you loft them. More on this later….
If you put the section curves into the “Loft” component in Grasshopper, if you edit the curves in Rhino, the surface, and anything associated with it will update. The curves can be edited by moving the control points of the lines. Click the line, and click the “show control points” button. In the example above I show how the surface might updated moving some control points vertically, and some horizontally.
Another thing you might try is playing with the Loft options. This controls how the program connects the three curves. A Loose Loft, for example, won’t be so strict connecting the control points together. It is like the difference between an interpolate curve through the points and a bezier curve where the points are only control points. Another option that could be useful is to rebuild your curves, although this will impact your geometry. What this does is it evenly divides each curve into an equal number of control points. This could prove useful if you are sketching curves and each curve has a different number of control points.
Above are a few common errors. In the first you can see the type of loft created when you select in Rhino the curves from the wrong end. Basically, Rhino will number the control points of each curve with the first point being the point closest to the end that you select with the mouse. So if you are careless you might get something looking like the first image. In the second I show what might happen if you select the curves in the wrong order, and in the third, what might happen if you choose a “closed” loft. In many cases, you will want a closed loft, but what it basically does is add the first curve again to the end of the list and it tries to wrap the surface back through the start. So in this case, it is definitely not what we want.
And here is an image of simple loft script.