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When you need to create smooth non-geometric curves, there's nothing better than a spline. Splines allow you to create free-form geometry that doesn't have to conform to strict dimensions. In this lesson, we're going to look at the new options available in AutoCAD 2011 for creating spline geometry. I'm going to start by opening up my Draw panel and I'll launch the Spline command. Take a look at the command line. Notice there's a new option down here called Method. I'm going to right-click and select Method from this menu.
In AutoCAD 2011, there's now two ways or two methods for creating a spline. There is the Fit method and the CV method. CV stands for control vertices. Let's look at the Fit method first. I'll select that and then I'll start picking some points on screen. The Fit method is very similar to how we've created splines in prior versions of AutoCAD. The arcs that I'm creating are based on, and pass through the fit point locations, where I'm clicking on the screen.
When I'm finished with my spline, I'll hit the Enter key on my keyboard. Let's look at some of these settings associated with the Fit option. I'm going to pan my drawing up. We'll launch the Spline command again and take a look at the command line. Notice there is an option down here called Knots. Once again, I'll right-click. We'll select Knots from the menu. This represents our Knot parameterization. Now there are three parameters we can choose from. Our Knot parameter affects the shape of the curve as it passes through the fit points.
Now what I'd like to do is create three splines, one using each parameter, such that we can see the difference. Chord happens to be the default, so I'll select that and I'm going to create my splines using these circular targets. That way all three splines have the same fit point locations. So let's draw our spline from the center of this circle to this one to this one. I'll connect them all and then I'll hit my Enter key. I will then hit the Spacebar to go back into the Spline command. I'll right-click and select Knots.
This time we'll use the Square root parameter. Before I draw my spline, I'm going to open up the Properties panel and I'll change my current color to red. This way we can tell the difference between the geometry. I will then move through and connect all of my center points, and I'll hit Enter. Let's hit the Spacebar again to re-launch Spline. I'll right-click and select Knots. Finally, we'll take a look at the Uniform parameter. As before, I'm going to open up my Properties panel and this time I'll change my current color to green.
Now as I draw the spline from center to center to center, take a look at my command line. Notice there is a setting down here called toLerance. At any point while creating any of these three splines, I could have adjusted this tolerance setting. Keep this setting in mind. It's going to be important in just a second. Let's finish up the spline. Then I'll hit Enter. When I zoom in, you really can't see much difference between the three options, that is, until we adjust our tolerance value. Tolerance controls the distance the arc is from the fit point.
Now the default tolerance setting is zero. That's why all of these arcs pas through the fit point. Tolerance and your Knot parameter kind of go hand in hand. As you increase the tolerance, your Knot parameter will have a greater effect on the shape of the spline. I'm going to back up just a little bit, and rather than redrawing these splines with a different tolerance, I'm going to create a crossing selection to select these and then I'll hit Ctrl+1 to bring up my Property Changer. I'll click-and-hold this slider and drag this to the bottom.
Let's change our Fit tolerance right here. I'm going to set this to 1 and hit Enter. Notice the change in the shape of splines. Once again, I'll click in the tolerance field and I'll set this to 2 and hit Enter. We can see the effect in our geometry. When I'm finished, I'll hit Escape to deselect my splines, and I'll close the Property Changer. Let's look at another setting associated with the Fit method. Maybe I'd like to create a nice smooth transition between these straight segments.
I'm going to launch my Spline command. I'll create my spline from the endpoint here, and let's take a look at this start tangency option. I will right-click and select that from the menu. Start tangency controls the direction at which I am exiting my start point. I will define that direction by Shift+Right-click. I'll select Parallel and I'll hover over this line to acquire the angle. I will then place my cursor on the other side to snap to that direction and I'll click.
I will then pick a point just about in between these endpoints. Notice as I move, my spline segment will always maintain its tangency to that line. I will draw my spline to the endpoint of this segment and then I will right-click and I'll select end Tangency this time. I would like to define the direction of my end tangency to be the endpoint of this segment. Using those tangency options, I was able to create a nice smooth transition between these straight- line segments. Let's back up.
I'm going to pan the drawing over and we'll find some open space here. This time, let's take a look at the control vertices method of creating a spline. I will launch the Spline command. I'll right-click and select Method. We'll choose CV and I'll pick some points on screen. Notice the difference. In this case, I'm creating control vertices, which define these angles that influence the way my geometry curves. Now that I'm finished, I'm going to hit the Enter key. When I'm finished with my spline, I'll hit Enter.
Let's take a look at some of the settings that are associated with the CV or control vertices method. I'm going to re-launch the Spline command and take a look at the command line. Whereas Fit has a Knots settings, CV has a Degree setting. I'm going to right-click and select Degree. Now there are three possible settings for Degree, 1, 2 or 3. The Degree setting controls the maximum number of bends you can have in each span. Once again, we'll create a spline using each setting, so we can see the difference.
I'm going to start with a Degree setting of 1 and I'll draw my spline to the center of each of these circles. With a Degree setting of 1, we have no curvature. Our spline is essentially nice, sharp, straight segments. I'm going to re-launch the command. I'll right-click and select Degree. This time, we'll try a value of 2. As before, I'm going to change my current color to red, so we can see the difference between the entities.
We'll connect the same centers. With a Degree setting of 2, I get a single curve or a parabolic curve in each one of these spans. Finally, we'll re-launch the command. I'll select Degree. We'll set this to a value of 3, which happens to be the default. I'm going to change my current color to ByLayer. With a Degree setting of 3, I can have two curves per span. We can easily see the reverse curve in this span in the middle.
Now that we've seen some of the new ways we can create spline geometry. Let's try and use some of these tools in a practical example. I'm going to zoom out. Let's pan the drawing over. On my screen, I have a civil engineering example. This is a drawing of a large wooded lot. I've got a pond right here. On the west side of the lot, I have an existing bike path. Now in this case, we're going to do some conceptual design. I would like to create the conceptual proposed centerline of a new bike path that deviates from the existing path and traverses through my property.
Then reconnect to the path in the southwest corner. To create my design, I'm going to zoom in. Then I will open up the layer control and I will set my current layer to the proposed centerline layer. I will then launch the Spline command and I would like to use the Fit method, because I would like to draw my spline using the fit points. The first point of my spline will be at the Shift+Right-click, nearest to right here. I'd like to use a start tangent, so I will right-click and select that from the menu.
I would like to define my start tangent direction by a point, Shift+Right-click, nearest to here. I'll back up a little bit and I'll pick my first fit point. Let me back up a little bit more, so we can center the lot on screen. I'll pick some more fit points to create my path. Now, this path is conceptual, so I can go any place I want. Because I'm using a spline, I can create this free-form geometry much faster than if I was using traditional commands like Arc and Line and Polyline.
I'm going to weave this right through here. Finally, I'll zoom in to do my connection. I would like to connect at a point, Shift+Right-click, nearest to here. Let's use an end tangent. I'll right-click and select end Tangency from the menu. I'd like its direction defined by a point nearest to here. There we go! Let's back up and take a look. This is going to be a 10-foot wide path. So I will launch my Offset command.
My offset distance will be 5 and I'll hit Enter. I would like to offset my centerline to this side. Let's zoom in a little bit. I will offset the centerline to this side. And I'll hit Escape when I'm finished. Finally, I will select the edges of my path. We'll open up the layer control. We will place these on the proposed edge of pavement layer. Splines are a great way to create smooth, fre- form geometry, without the need for entering specific dimensions. In AutoCAD 2011, we have even more flexibility and control when creating our spline geometry.
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