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Monday, June 2, 2008

Getting more from your solids

It seems that everyone is using solids now, the only problem is when one solid object passes behind another, or more specifically for CADWorx Plant, how to show a line that passes under the platform/deck (or even equipment if you like). Hopefully everyone has discovered that if you try to make 3D deck grating it makes a really huge (file size) model. And that makes it hard to navigate around. So what can we use instead of 3D decking? By using modeling objects like Solids or Regions along with the Grate hatch pattern.
A lot of folks are using a solid box to represent the foundation (and other concrete objects). We can also create a solid based on the “open” bay of the structure.

Let’s set the scene, we have a steel frame drawing referenced into our piping model along with equipment. As we route the design we notice that a line passes below the decking in one bay. What we would like to see when we plot are hidden lines as it passes beneath the deck (without having to actually draw any additional geometry).

So here we are looking at both the SW Isometric and plan view. Our piping extends beyond the structure. So to make it appear that the piping that extends into the structure is “hidden”, the first thing we need is either an AutoCAD solid or a Region. In either case you will need to create a Boundary. You have 2 choices when creating a Boundary; to create a Polyline closed shape or a Region.

To create a solid as representing the deck, one quick method is to use the PRESSPULL command after creating a Polyline Boundary. So to start that procedure you would start the Boundary command, choosing the Polyline object type. Then select the “Pick Points” tool and select in the bay that you need. It’s a good idea to turn off your piping layers (including the CL layer) as the Island detection will find the centers and solid pipe as well. You will notice that even though you select in the open bay, your current AutoCAD elevation is still applicable (see the dotted outline at “0” EL.).

So at this point you have the option of either editing the boundary properties to adjust the elevation (say to 10’ or what ever the T.O.S. is), or set your current elevation before you start the command. I usually just edit the elevation, that way I can pick the bays in the plan and adjust as needed (including copying if necessary from one deck elevation to another. Once the boundary is at the correct elevation, to create a solid to represent the deck you can then use the PRESSPULL command and select in the boundary you just created, then pull vertically and enter the thickness of your decking (about ½” minimum).
Or to speed things along, you could forgo the entire Presspull command and when you create your Boundary, choose the Region option. Yes, you will still have to adjust for the elevation, but once your have the Region at the correct elevation, your set to go on to the system variables that will give you hidden lines when you print/plot.

So now that we’ve turned back on our piping layers, let’s take a minute to review some other settings.
Your viewport should be on a layer that does not plot (Viewl), along with your router line (I recommend putting the router on the system layer), the System (bolts and gaskets) and the Dim2 (View box) layers. Don’t turn these layers off or freeze them, it works better if we can see them, we just don’t need these layers to print/plot.
The next thing is to ensure that the viewport is set to “Hidden” under the Shade plot options, not “3D Hidden”, just plain “Hidden”.

If you do a Plot Preview at this point we can see that the solid object (yes Regions are considered solids, just really, really thin solids) is obscuring the piping that passes below it.

The first system variable that we will adjust is OBSCUREDLTYPE.
This specifies the linetype of obscured lines. Obscured linetypes are independent of zoom level, unlike regular linetypes. The linetype values are defined as:
0 - Off
1 - Solid
2 - Dashed
3 - Dotted
4 - Short Dash
5 - Medium Dash
6 - Long Dash
7 - Double Short Dash
8 - Double Medium Dash
9 - Double Long Dash
10 - Medium Long Dash
11 - Sparse Dot

So once we have set that to, say Dashed (2), the preview now looks like this:

Notice that the centerlines are being picked up in this as well, but as simple dashed lines not the center lines that we like (yup, 2D Rep is still the best way to go for center line representation in the plans/sections).

Just in case you were wondering, an obscured line is a hidden line made visible by changing its color and linetype. OBSCUREDLTYPE is available only in 2D views. In 3D views, the VSOBSCUREDLTYPE system variable is used. But since we are creating plans and sections, they are 2D.

HALOGAP is the next variable we will look at. This specifies a gap to be displayed where an object is hidden by another object. The value is specified as a percent of one unit and is independent of the zoom level.
So if we set it at a value of 5, then it produces a gap like we see here:

(I turned the Cl layer to be frozen in the current viewport to cut down on the confusion). Notice the difference between the setting of 0 on the left and 5 on the right. I usually recommend that you make a few adjustments so that it looks right.

Much like OBSCUREDLTYPE, HALOGAP is available only in 2D views. In 3D views, the VSHALOGAP system variable is used
The last variable is OBSCUREDCOLOR. For those of you able to print/plot in color, this specifies the color of obscured lines. Value 0 designates ByBlock, value 256 designates ByLayer, and value 257 designates ByEntity. Values 1-255 designate an AutoCAD Color Index (ACI).
So if I set the color to 3 (Green), the preview will look like this:

I know this looks wild, but keep in mind it is trying to do just what we told it, show all of the obscured lines as green and dashed. And since these are all 3D objects, the “underside” of every component is obscured. Don’t worry though, the solid lines will “hide” all of the redundant line work from your print/plot (it’s hard to see a dashed line where there is also a continuous line).
An obscured line is a hidden line made visible by changing its color and linetype. And just like the previous variables, OBSCUREDCOLOR is available only in 2D views. In 3D views, the VSOBSCUREDCOLOR system variable is used.
Just a reminder, the OBSCUREDCOLOR setting is visible only if the OBSCUREDLTYPE system variable is turned on by setting it to a value other than 0.

Now over the years some of you folks have discovered the SOLPROF command. However this has one major drawback, it creates 2D blocks and layers in your drawing. The same can be said of the SOLVIEW command as well. Although SOLVIEW is best used for aligned section and detail views in Vanilla AutoCAD, as it also creates named views. Personally I like using the View Box in CADWorx better, but in a pinch it works.

(Note: All images created using AutoCAD 2009)

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