Creating editable surfaces

What is the best way to create an editable surface that represents topography?
I have tried several approaches

Using a series of curves representing topography placed at correct z elevation you can use patch command to create a surface.

Type of surface you can create can be so different - it’s a bit baffling.
For instance, look at image 22 02 21a.
Here you can boolean surface but cannot turn on editable points
It says it cannot turn on control points for an open polysurface

If you look at image of second file: 22 02 21b
Using patch command based on topographic lines creates something whose object type is simply listed as surface
This works both with boolean operations and with editable control points
When I move up points to create a hillside, resultant surface is not a curved as i would like. How do I change this? Should I have used a different stiffness value in original patch command?

Experimenting with this I originally used a model whose surface Area was a closed solid polysurface
It also had a mesh which had editable points
polysurface does not have editable points

So what is best way to create editable surfaces? was creating something whose object type is simply listed as surface a bit of a fluke? Will this surface continue to be editable and does anyone have have any thoughts on the best way to create editable surfaces?

I don’t have answers to all of your questions, and I haven’t finished my coffee, but fwiw I think you can get around some of the limitations you are running into by using CageEdit.

Bottom line is that surfaces are point-editable but polysurfaces are not. The complexity of a surface limits how much detail you can add by point-editing alone. CageEdit can help you make smooth changes to complex surfaces and can also help you edit polysurface shapes independent of the complexity of the underlying geometry.

Another thing that might help is Subd surfaces. I don’t do topography, so I don’t know how useful subds are for that, but seems like they could be very useful.

Kig0064 The basic geometry elements in Rhino are curves and surfaces. A surface has an array of control points arranged in rows and columns, and the surface can be edited by moving the control points. It is also important to note that a surface can be trimmed so that only a portion of the surface is used.

Two or more surfaces can be joined together into a polysurfaces. This enables very complex geometry to be represeneted. Rhino does not allow access to the control points of the constiuent surfaces of a poysurface.

As Peter suggested a polysurface can be modified using CageEdt. Another method to modify a polysurface is to either Explode the polysurface into individual surfaces, or use ExtractSrf (with Copy=No) to extract a single surface from a polysurface. Edit the individual surfaces as desired. Join the surfaces to recreate the polysurface. If the edges of the surface have been altered then the edges of adjacent surfaces will need to be matched using MatchSrf. (Adjacent surface edges need to be within the absolute tolerance for surfacss to be joined.)

The stiffness parameter in Patch affects how Patch creates the surface. It does not affect the resulting surface after it is created. Experiment with the number of spans in each direction.

Kig0064 How much experience do you have using Rhino?