While browsing the new help topics for Rhino 8, I figured out that certain tools lack a complete description and cautions. For example, the EdgeSrf tool is presented with scarce information, which could mislead the new Rhino users that this is just some basic tool that don’t need much attention. In fact, it’s one of the most valuable tools in Rhino and, sadly, many people skip it, because they are unaware of its advantages when it comes to NURBS surfacing with single-span surfaces.
That page does not mention that the EdgeSrf tool is capable of creating surfaces with the minimum amount of control points to achieve the desired shape. Along with that, this tool could precisely match the input geometry when it has the same number of control points and degree. This is the preferred method to build primary surfaces that are then modified via manual control point editing and/or matching its edges to the adjacent geometry.
Furthermore, the EdgeSrf tool has a specific way of building 4-sided surfaces, but this is also not mentioned in the help topics. To build a proper 4-sided edge surface from 3 input surface edges or curves in a П-like configuration, the middle input edge/curve must be selected first, then the side ones. If the order of picking the edges/curves is different, the resulting surface will be highly distorted and even many not align with the input geometry.
I can go on and on with giving examples with other tools that have an incomplete information, but you get the idea. I’m aware that making such a broad documentation takes a lot of time and effort due to the huge amount of tools in Rhino, but this and other tools were in existence for many years, yet their help topics lack a lot of useful information that could help the existing and new Rhino users.
Still no mention about the very important rule to pick first the middle curve or surface edge from the 3 input curves or surface edges in a П-shaped configuration, in order to to build a 4-sided surface…
I’m not sure if we should include this special case, since it isn’t the way most users typically use the command. Perhaps the best solution is to fix the command so it always creates a four-sided surface, regardless of the picking order.
And picking the middle curve first may not always create a four-sided surface.
I don’t know if its really true that most users do not use the command to make a 4-sided surface from 3 curves, but if it is true maybe that’s because the Help is not helpful in explaining how to do that.
You’re not showing the rather typical case - three surface edges/curves, all coming to a point in pairs. A three sided EdgeSrf then gives you a zero-length fourth edge with a proper singularity.
It’s very often used by me and many other Rhino users to build a 3-sided or 4-sided surface from 3 curves or surface edges. I consider this tool as the best way to build a clean starting surface for subsequent control point massaging, which is important for everyone who aim to achieve good surface quality.
The requirement to pick the middle curve or surface edge first is opposite to the “Sweep 2 rails” tool which requires to pick the side curves or edges first.
Perhaps the best solution is to just fix the bug in “EdgeSurf”. Until then, I believe that the newbies will benefit from knowing about the specifics related to the picking order.
Currently if 3 edge curves are selected with a small gap between curves then EdgeSrf always (independent of selection order) creates a 3-sided surface (actually a 4-sided surface with one zero length side). This avoids the creation of a 4-sided surface with a very short side which is likely to cause problems which are difficult to diagnose. If the user wants to create the 4-sided surface with a very short side from the 3 edge curves with a gap they can do so by inserting a short line to close the gap. If the gap is sufficiently large then a 4-sided surface can be created.
The revised EdgeSrf should continue to avoid creating surfaces with very short sides unless the user intervenes.
I think that users who want to build a 3-sided surface from 3 curves will make sure that they form a closed triangle before running the “EdgeSrf” command.
A set of curves or surface edges that form an “open triangle” should create a 4-sided surface. If Rhino creates a 3-sided surface instead, that leaves a degree of an unwanted deviation due to the sides of the “EdgeSrf” not following the input geometry accurately.
If Rhino makes a surface from edges that is not within tolerance of the curves used to create it that is also creating a problem for users.If the users attempts to use matchsrf to get the edges to match that will create more problems. In other words, by making a singularity to avoid a short edge Rhino is creating a series of problems in an attempt to avoid what is not usually a problem at all.
A short edge that is longer than double the document tolerance usually doesn’t create problems. If the end gap between two curves used for EdgeSrf is less than twice the document tolerance than it should create a singularity because the surface created will be within tolerance of the curves used to create it.
Right now it looks like Rhino creates a 3 sided surface to avoid making a 4-sided surface with a short edge that can be 1000 times greater than the users tolerance. That is not veryl useful.
This is a really confusing behavior. If I opt to build a 4-sided surface, I would expect it to stay that way in the future, too (unless I run some command to convert it to 3-sided).
I’m aware that making such a broad documentation takes a lot of time and effort due to the huge amount of tools in Rhino, but this and other tools were in existence for many years, yet their help topics lack a lot of useful information that could help the existing and new Rhino users.
