In Part 2 of this series
of posts about splines, I mentioned Tolerance as one of the options that we can
tweak when doing Spline Freehand.
Tolerance will determine
how close the curve will be to the points we define. Tolerance in 0 will force
the curve to be interpolated through all the points. This value is
tightly related to Increment. But we’ll explain Increment in a following post.
For the time being, imagine that while you do the stroke when sketching (with
mouse or stylus), AutoCAD is recording the position of your pointer, and
keeping some of those values (yes, that’s the increment). According to the
amount of points that AutoCAD registers, then Tolerance kicks in. A 0 Tolerance
will force the curve to be interpolated through all the points, as I already
mentioned. When you change Tolerance to higher values (being 1 the maximum),
you will get less points along the spline, which will obviously make it
smoother.
Let’s check the
following captures.
I made four sketches,
roughly similar in terms of the hand’s gesture. They look quite different.
They are ordered
according to the Tolerance used. 0, 0.2, 0.5 and 1. My previous explanation
should now be really clear. As I move up in Tolerance, the spline gets
smoother.
By using CVSHOW command
(located in the Control Vertices tab, we can check out the amount of CVs we got
from the sketching. I got 115 CVs on the spline with Tolerance=0, and 9 CVs on
the one with Tolerance=1. Imagine which is easier to control J
As a best practice, I
would recommend to stay closer to 1 than to 0, and always watch the Increment.
Since this setting is based on units, it has to be related to what you are
drawing, so there are no recipes. If your spline belongs to the side of a
consumer product, and depending on the units, the increment needed will be very
different to the one you want if you are sketching the roof of a huge
convention center.
By the way, the Spline
Freehand settings are only available through Command Line.
See you next post, when we’ll cover Increment and make an example.
Last post I promised to show how to make a spline made out of a sketch more usable. So here's the answer.
There is an option in the Surface tab called Rebuild. The command REBUILD works both on splines and surfaces. If you click on a spline after invoking the command, you will get the one and only task dialog in the entire surface modeling feature. This dialog will show the current amount of Control Vertices and the current Degree on the spline (I’ll explain about the degree of a spline in another post). You can define a new CV count and a new degree. By default, the degree will be 3, and you may probably be ok with that. The amount of CVs will vary according to the increment and size of the sketch you did.
So how can you know which is the correct amount of CVs? Simple. There’s a Preview option which will show both splines, and a little icon that determines the maximum difference between both of them. This is called Maximum Deviation. While you’re in Preview, you can either hit Enter to finish the operation or click Escape to get back to the task dialog. If you do that, you will see the exact value of the Maximum Deviation.
There’s another option to Delete the original spline. This is probably what you want, but as usual, there’s an option for pretty much everything in AutoCAD.
As you can see, you can start a design with the best tool ever created for sketching: your hand. The other good news is that you can add control to what your hand did. Can you ask for more?Let’s get back to the splines.
Let’s start with the last option in the drop down, which is the old SKETCH command, now defined as Spline Freehand.
Remember how SKETCH worked in the past? Pen up, pen down, and finally you got thousands of little segments, probably not usable unless you did some workarounds, like converting them into a polyline, and making a spline fit, if what you wanted was a curve. If you seldom use it, this is probably the reason.
But now there are no excuses! This command has been updated, and can now produce not only lines, but also polylines and splines. We can also determine the Tolerance and the Increment. These options will make a lot of sense when using Spline Freehand. The bigger the Increment, the less CVs the spline will have. If you want a lot of control over the curve and need more control of smaller details in the geometry, a smaller Increment will help. Tolerance will determine how close the curve to the points that define it is. Tolerance in 0 will force the curve to be interpolated through the points.
This command will make much more sense when you use a tablet, since it will be maximizing the power of the control you have on your hand while sketching. Nothing can match the gesture of a hand making a stroke. There are now many options for tablets starting at very reasonable prices, so feel free to check them out, and add them to your list of gadgets (we all love gadgets, don’t we?).
You can then draw many sketches, which will become individual splines or polylines once you hit Enter. If you select any of the splines you just created, you will notice that they may have many Control Vertices (depending on the Increment). If that is the case, or your sketch is a little rough, you may ask yourself how you can make this usable. Of course, there’s an answer for that in AutoCAD 2011 too! (but not today J)
With so much to cover about AutoCAD 2011, it’s hard to decide where to start. But since surface modeling is probably the biggest news in terms of new object types, commands and workflows, it looks like a smart place to begin the AutoCAD 2011 posts.
Before diving into the surfaces, let’s talk about an AutoCAD citizen that has been around for a while, and that certainly needed some enhancements. I’m talking about the splines.
So why work on splines? First of all, in order to have healthy surfaces, we need to be able to make better splines than what we had available. Secondly, since we added multi functional grips for polylines, it seemed to be the right time to make the editing consistent.
All this release, as last release, has made improvements in direct manipulation. You may have seen that we have tried to eliminate as many dialog boxes as possible (have you checked hatch already?). Not being disrupted by a dialog box, and being able to always focus on the object, will really help you improve productivity. In other words, you will finish your work faster.
Back to splines. If you move into the 3D Modeling workspace (you can do that from the Quick Access Toolbar or from the gear icon at the right of the status bar), you will notice there’s a new tab called Surface. This tab contains a panel called curves, and Splines have the lead role here. If you need to work on splines for 2D drafting, you may consider either remembering the options, or directly customizing your UI in order to have these icons on your Draw tab in the 2D workspace.
So what’s new? Well… where can I start? Now we have three methods for creating splines. We just had one in the past, which was the SPLINE command. It created a spline through Fit Points. That option is now called Spline Knot, and you can find it in the drop down under Spline CV. The second method we’ll cover is Spline CV. This enables you to create a spline through Control Vertices. If you have used splines in other packages, you will know what I mean. If not, I’m going to cover the fundamentals in a following post. The third method is Spline Freehand. This is the good and old SKETCH command, which has been enhanced. If you have a tablet, you’ll love the new Spline Freehand.
In the next post I’ll cover Spline Freehand extensively.
For now, just try something (assuming you already have 2011). Start SPLINE command, and do whatever you did in the past in order to draw a spline. Now hit Enter. Guess what? No more three annoying clicks in order to define tangencies! Yay!
See you later. My plane is landing in LA, and I have a long day ahead speaking about AutoCAD.
