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By definition the Offset command creates parallel copies of your geometry at a specified distance, and in most cases the offset command works just fine. However, if you offset a polyline you'll find that your specified distance is not consistent along the entire length of the copy. In this lesson we are going to learn how to create offsets that reflect a true offset distance. On my screen I have an architectural example. This cyan geometry represents a swing set. The swing set is sitting in a large play area filled with sand and these magenta lines represent a concrete boundary.
I also have a couple of trees. Now all playground equipment has a suggested safety zone that is recommended by the manufacturer. This particular swingset requires a 10 foot safety zone surrounding the equipment. My question is, do I have enough room within this concrete boundary to accommodate the swingset plus the necessary safety zone? First, let's identify the rough boundary of the swing set. I am going to launch the Polyline command. Note that I've created a layer called safety zone and I've set that layer current.
I am going to grab the endpoint here and here and I'm going to trace around the outside of this geometry. Over the endpoint here and here, here and here, and then I'll right-click and select Close to close my shape. Now let's offset this geometry 10 feet. I'll launch the Offset command. My distance will be 10 feet. Enter. I'll select my boundary and I'll offset it to this side.
At first glance it looks like I need to use a smaller swing set or increase the size of the concrete boundary. Let's take a few measurements. I am going to zoom in. We'll launch the distance command and we'll find the distance from the midpoint of this edge perpendicular to the offset. As you can see that's 10 feet. However, let's find the distance from the endpoint here to the endpoint here. As you can see this measures more than 11.5 feet.
So why does a 10 foot offset not a 10 foot offset? When it's in outside corner. In order for this offset to show me all points 10 feet away from this equipment, these corners would have to be round. Fortunately, there is a system variable that will do this for me automatically. Let's zoom out and I'll center this and I'm going to type OFFSETGAPTYPE, and I will press Enter and I'll change its value to 1 and press Enter. Now when I use the Offset command on a polyline, AutoCAD will create rounded outside corners.
Let's erase this original offset. I'll launch the Offset command again. I'll press Enter to accept the distance of 10 and I'll offset my boundary to the outside. This offset represents all points 10 feet from my boundary edge and as you can see this equipment should work perfectly within my concrete boundary. I have just enough room for the safety zone recommended by the manufacturer. Now I would consider OFFSETGAPTYPE to be kind of a special occasion system variable. You probably don't want this running all the time, so I'm going to set mine back to 0.
I'll do that by right-clicking, I'll select Recent Input, I'll grab OFFSETGAPTYPE from here, and I'll set this to 0. The OFFSETGAPTYPE system variable is a great tool to have in your AutoCAD toolbox for the next time you need to create a true offset.
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