What a Mesh

Splines in AutoCAD 2011 part 4 - Setting Tolerance in Spline Freehand

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.

Splines in AutoCAD 2011 part 3 - Optimizing your sketch

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?

Splines in AutoCAD 2011 part 2 - Sketching

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)